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Transcript
To: NASA SMD Product Evaluation Team
From: AMS Education Program Staff
AMS submits for NASA SMD Product review six of its DataStreme Earth’s Climate System
(ECS) Investigations Manual activities. These include:
1A
1B
2B
3A
5A
9B
MODERN CLIMATE SCIENCE
Defines “climate”, introduces Earth’s climate system and investigates the AMS Climate
paradigm
FOLLOW THE ENERGY! EARTH’S DYNAMIC CLIMATE SYSTEM
Presents a simplified model of Earth’s energy system to receive and emit radiation
CLIMATE VARIABILITY AND CHANGE
Investigates a unique case of one possible climate change cause
SOLAR ENERGY AND EARTH’S CLIMATE SYSTEM
Contrasts the global distribution of incoming solar energy at various latitudes
GLOBAL WATER CYCLE
Investigates remote sensing of Earth’s global water cycle
METHANE HYDRATES: MAJOR IMPLICATIONS FOR CLIMATE
Demonstrates one climate system component that may trigger rapid system change
These activities are part of the printed Manual containing 30 total activities. The Investigations
Manual is a major component of the NASA-supported DataStreme ECS K-12 teacher
professional development course, which also includes a printed textbook, course website, and
additional teacher support materials.
The submitted PDF document contains reference materials to provide context for the 6 activities
to be evaluated. These materials include the Investigations Manual introduction section and table
of contents (also used for our undergraduate level AMS Climate Studies course), Chapter 1 of
the course text, and a summary of how DataStreme ECS relates to the National Science
Education Standards.
For reference purposes only, the DataStreme ECS course website address is:
http://www.ametsoc.org/amsedu/ECS/home.html
1A - 1
Investigation
1A:
MODERN Climate Science
Driving Question: What is Earth’s climate system and what are the empirical and
dynamic definitions of climate?
Educational Outcomes: To identify some of the many reasons for studying Earth’s
climate system. To learn more about the workings of Earth’s climate system and become
more aware of the significance of climate, climate variability, and climate change for our well
being wherever we live.
Objectives: AMS Climate Studies is an innovative study of Earth’s climate system that
promises to deliver new understandings and insights into the role of climate in our individual
lives and the broader society. The AMS Climate Paradigm presented in this Investigation
employs an Earth system science approach.
After completing this investigation, you should be able to:
• Describe Earth’s climate system and its interacting components.
• Describe, compare and contrast the complementary empirical and dynamic definitions of
climate.
• Explain the AMS Climate Paradigm.
An Earth System Approach:
AMS Climate Studies employs an Earth system perspective. A view of the Earth system as
seen from space is presented in Figure 1. The image shown is a visible light full-disk view
from a U.S. weather satellite positioned about 36,000 km (22,300 mi) above the equator
in South America at 75 degrees W longitude. The satellite remains at that location relative
to Earth’s surface because it makes a full revolution around the planet as Earth makes one
rotation in the same direction. Being geostationary, the satellite provides a continuous
view of the same underlying surface. Successive images from this vantage point provide
animations of whatever can be seen moving across Earth’s surface, including the boundaries,
called terminators, which separate the illuminated day side and dark night side of our planet.
Examine Figure 1, noting the outlines of land masses. The center of the disk is the point
on Earth directly under the satellite from which this image was acquired. Place a dot on
the image to represent this sub-satellite point and draw a horizontal line, representing the
equator, through the point and extended to the edges of the Earth disk. Approximately onethird of Earth’s surface can be seen from the satellite.
1. Figure 1 is a view of the Earth system with the edge of the disk marking the boundary
between Earth and the rest of the universe. It is evident from the sharpness of the edge
between Earth and space that the atmosphere must be a thin layer compared to Earth’s
diameter. Since the full disk appears sunlit in this visible image, the local time at the subsolar point must be near [(noon)(sunset)(sunrise)].
Climate Studies: Investigations Manual 3rd Edition
1A - 2
Figure 1.
Visible image of Earth from NOAA GOES East satellite at 1745 UTC on 1 March 2012. The time was
12:45 pm EST, 11:45 am CST, 10:45 am MST, 9:45 am PST.
2. Compare land and ocean surfaces in this view. As would be seen from other vantage
points in space as well, Earth’s surface is [(more)(less)] water than land.
Figure 1 is a static view of Earth’s climate system. For a view of it in motion, go to:
http://www.ssec.wisc.edu/data/geo/index.php?satellite=east&channel=vis&coverage=fd
&file =jpg&imgoranim=8&anim_method=flash , or http://www.ssec.wisc.edu/data/geo/
index.php? satellite=east&channel=vis&coverage=fd&file=jpg&imgoranim=8&anim_
method=jsani
Short Cuts! Please note that all web addresses appearing in these
investigations are available on the course website by clicking on
“Investigations Manual Web Addresses”. Under the particular
Investigation heading, click on the link shown. The website above also
can be accessed via QR coding presented at the right.
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1A - 3
You are viewing the University of Wisconsin Space Science and Engineering Center (SSEC)
website from which Figure 1 was acquired. The animation that appears is composed of eight
recent full-disk images from the GOES East satellite, most acquired at three-hour intervals
with the latest being only a few hours old. View the animation that essentially covers one
day as it repeats through several cycles. To look at individual images or to slow down the
animation, use the control bar above the image. First, click on “stop”. Then click successively
on the step-forward (>) button while noting the progression of day and night on Earth’s
surface as the rotating planet intercepts the radiant energy from the distant Sun.
3. Half of Earth’s surface is in sunlight and half in darkness. The sunlit portion in the
image shows the part of Earth in the satellite’s field of view that is receiving energy from
outside the Earth system. The animation shows that the solar energy coming into the
Earth system at any location is [(continuous, constantly illuminating the surface)
(received in pulses, alternating between periods of sunlight and no sunlight)].
4. The time of each image is printed across the top, after the date. Stop the animation at the
1745 UTC image, the same time of day as the Figure 1 image. Compare it with Figure 1.
The major observable differences in the two images arise from the Earth system’s
[(land surfaces)(ocean surfaces)(atmosphere)].
Because these images are visible light images (essentially conventional black and white
photographs), features are distinguished by the variation and quality of reflected sunlight.
Generally, the brighter (whiter) the feature, the greater the reflection of solar radiation
directly back to space. Conversely, darker areas indicate greater absorption of the incoming
solar energy.
5. Generally, the image shows that [(land surfaces)(water surfaces)(cloud tops)] are places
where the greatest amount of incoming solar energy is absorbed into the Earth system.
On the SSEC Geostationary Satellite Images browser menu to the left, click on the Imager
Channel “Longwave IR 10.7 μm” button. Here you are viewing images of “heat” radiation
emitted by the Earth system out to space. In these IR images, the darker areas represent
those places where outgoing heat radiation to space is greater, and lighter areas denote less
outgoing heat radiation. Essentially, these are images of temperature. The darker the shading,
the higher the temperature of the surface from which the radiation is being emitted and the
greater the rate at which heat energy is being lost to space.
6. Comparison of the IR animation with the visible light animation shows that the Earth
system emits IR to space [(continuously)(only on the night side of Earth)].
7. Step through the IR animation for several cycles and look for broad, essentially cloudfree places where shading changes most, that is, they alternate between dark shading
(meaning they reach relatively high temperatures) and light shading (meaning cooler
temperatures) over the period of a day. These locations are [(land)(water)] surfaces.
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1A - 4
8. Stop the IR animation on the image with places shaded darkest and note the time of the
image. Switch to the visible imagery by going to the browser menu and stopping the
animation at the same time. The comparison shows that the highest surface temperatures
occur within a few hours of local [(midnight)(sunrise)(mid-day)].
In summary, you have been introduced to the Earth system, the receipt of sunlight into the
Earth system from space (incoming energy), and the emission of IR (heat) from Earth to
space (outgoing energy).
That part of our planet (including the atmosphere, ocean, land, biosphere and cryosphere)
subjected to solar energy flowing into, through, and out of the Earth system, is Earth’s
climate system.
Weather, Climate and Climate Change:
Fundamental to an understanding of weather, climate and climate change, is the recognition
that the Earth’s climate system is a complex system of energy flow, as alluded to by
animations of visible and IR full-disk views of Earth. The observable impacts of the energy
flows (and the associated mass flows) are embodied in the descriptions of weather and
climate.
Weather is concerned with the state of (i.e., conditions in) the atmosphere and at Earth’s
surface at particular places and times. Weather, fair or stormy, is not arbitrary or capricious.
Both its persistence and its variability are determined by energy and mass flows through the
Earth system.
Climate is commonly thought of as a synthesis of actual weather conditions at the same
locality over some specified period of time, as well as descriptions of weather variability and
extremes over the entire period of record at that location. Climate so defined can be called
empirical, i.e., dependent on evidence or consequences that are observable by the senses. It is
empirical as it is based on the descriptions of weather observations in terms of the statistical
averages and variability of quantities such as temperature, precipitation and wind over
periods of several decades (typically the three most recent decades).
Climate can also be specified from a dynamic perspective of the Earth environment as a
system. The definition of Earth’s climate system must encompass the hydrosphere including
the ocean, the land and its features, the biosphere, and the cryosphere including land ice and
snow cover, which increasingly interact with the atmosphere as the time period considered
increases. While the transitory character of weather results from it being primarily an
atmospheric phenomenon, climate exhibits persistence arising from it being essentially an
Earth system phenomenon.
From the dynamic perspective, climate is ultimately the story of solar energy intercepted by
Earth being absorbed, scattered, reflected, stored, transformed, put to work, and eventually
emitted back to space as infrared radiation. As energy flows through the Earth system,
Climate Studies: Investigations Manual 3rd Edition
1A - 5
it determines and bounds the broad array of conditions that blend into a slowly varying
persistent state over time at any particular location within the system.
Whereas the empirical approach allows us to construct descriptions of climate, the dynamic
approach enables us to seek explanations for climate. Each has its powerful applications.
In combination, the two approaches enable us to explain, model and predict climate
and climate change. In this course we will treat climate from the two complementary
perspectives.
9. In its definition of climate, the AMS Glossary of Meteorology, 2nd. ed., 2000, states
that climate “… is typically characterized in terms of suitable averages of the climate
system over periods of a month or more, taking into consideration the variability in time
of these average quantities.” This definition is derived from a(n) [(empirical)(dynamic)]
perspective.
10.The AMS Glossary’s definition continues: “… the concept of climate has broadened and
evolved in recent decades in response to the increased understanding of the underlying
processes that determine climate and its variability.” This expanded definition of climate
is based on a(n) [(dynamic)(empirical)] perspective.
11.Local climatic data, including records of observed temperature, precipitation, humidity,
and wind, are examples of [(dynamically)(empirically)] derived information.
12.The determination of actual climate change, also from the AMS Glossary, (“any
systematic change in the long-term statistics of climate elements sustained over several
decades or longer”) is based primarily on evidence provided from a(n) [(dynamic)
(empirical)] perspective.
13.Also from the AMS Glossary, “Climate change may be due to natural external forcings,
such as changes in solar emission or slow changes in Earth’s orbital elements; natural
internal processes of the climate system; or anthropogenic (human caused) forcing.”
This is a statement derived from a(n) [(dynamic)(empirical)] perspective.
14.Scientific predictions of such an altered state of the climate (i.e., climate change)
must be based on treating Earth’s climate system from a(n) [(dynamic)(empirical)]
perspective.
Earth’s Climate System (ECS) Paradigm:
Utilizing a planetary-scale Earth system perspective, this course explores Earth’s climate
system. In pursuing this approach, understanding is guided and unified by a special
paradigm:
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1A - 6
AMS Climate Paradigm
The climate system determines Earth’s climate as the result of mutual interactions
among the atmosphere, hydrosphere, cryosphere, geosphere, and biosphere and
responses to external influences from space. As the composite of prevailing weather
patterns, climate’s complete description includes both the average state of the
atmosphere and its variations. Climate can be explained primarily in terms of the
complex redistribution of heat energy and matter by Earth’s coupled atmosphere/
ocean system. It is governed by the interaction of many factors, causing climate to
differ from one place to another and to vary on time scales from seasons to millennia.
The range of climate, including extremes, places limitations on living things and a
region’s habitability.
Climate is inherently variable and now appears to be changing at rates
unprecedented in recent Earth history. Human activities, especially those that alter
the composition of the atmosphere or characteristics of Earth’s surface, play an
increasingly important role in the climate system. Rapid climate changes, natural or
human-caused, heighten the vulnerabilities of societies and ecosystems, impacting
biological systems, water resources, food production, energy demand, human health,
and national security. These vulnerabilities are global to local in scale, and call for
increased understanding and surveillance of the climate system and its sensitivity to
imposed changes. Scientific research focusing on key climate processes, expanded
monitoring, and improved modeling capabilities are increasing our ability to
predict the future climate. Although incomplete, our current understanding of the
climate system and the far-reaching risks associated with climate change call for the
immediate preparation and implementation of strategies for sustainable development
and long-term stewardship of Earth.
15.It is implied in the AMS Climate Paradigm that components of Earth’s climate system
(e.g., atmosphere, hydrosphere, cryosphere, geosphere, and biosphere) interact in a(n)
[(random)(orderly)] way as described by natural laws.
16.This interaction of Earth system components through natural laws would imply a(n)
[(dynamic)(empirical)] perspective for climate studies.
17.The ocean as an Earth system component and player in atmosphere/ocean energy and
mass distributions suggest it is a [(minor)(major)] part of biogeochemical cycles (e.g.,
water cycle, carbon cycle) operating in the Earth system.
18.According to the AMS Climate Paradigm, our understanding of Earth’s climate system is
incomplete. Nonetheless, it states that the risks associated with climate change call for the
development and implementation of [(sustainable development strategies)
(long-term stewardship of our Earthly environment)(both of these)].
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1A - 7
Summary:
In this course we will investigate climate, climate variability, and climate change through
complementary empirical and dynamic approaches guided by the AMS Climate Paradigm.
Please note that Figure 1 and all other Investigations Manual images are also available on the
course website. To view these images, click on the “Investigations Manual Images” link on
the website, go to the row containing the appropriate investigation name, and then select the
appropriate figure within that row. For example, to view Figure 1 online, go to the row labeled
“1A” and then select “Fig. 1”.
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Climate Studies: Investigations Manual 3rd Edition
Investigation
1B:
1B - 1
follow the energy!
Earth’s dynamic Climate System
Driving Question: How does energy enter, flow through, and exit Earth’s climate system?
Educational Outcomes: To consider Earth’s climate as an energy-driven physical
system. To investigate fundamental concepts embodied in considering Earth’s climate from a
dynamic perspective and through the use of models.
Objectives: The flow of energy from space to Earth and from Earth to space set the stage
for climate, climate variability, and climate change. After completing this investigation, you
should be able to describe fundamental understandings concerning:
•
•
•
•
The global-scale flow of energy between Earth and space.
The impact of the atmosphere on the flow of energy to space.
The effect of incoming solar radiation on Earth’s energy budget.
The likely effects of energy concentrations and flows on Earth system temperatures.
Earth’s Dynamic Climate System
Earth’s climate is a dynamic energy-driven system. The radiant energy received from
space and that lost to space on a global basis determine whether or not Earth is in a
steady-state condition, cooling, or warming. An unchanging balance between incoming
and outgoing radiation produces a steady-state and stable climate. Lack of a balance between
incoming and outgoing radiation implies a net loss or gain of radiant energy to Earth’s
climate system. One result of such an energy imbalance is climate change.
Earth’s climate evolves under the influence of its own internal dynamics and because of
changes in external factors that perturb the planet’s energy balance with surrounding space.
The three fundamental ways in which this energy balance can be disturbed are by
changes in the amount of:
1. solar radiation reaching the Earth system;
2. incoming solar radiation that is absorbed by the Earth system; and,
3. infrared (heat) radiation emitted by the Earth system to space.
Solar radiation intercepted and absorbed by Earth drives our planet’s climate system. Earth
responds to this acquired energy through the emission of long-wave infrared (heat) radiation
as its climate system adjusts towards achieving global radiative equilibrium with space.
Because the amount of solar energy intercepted by Earth can be determined with great
accuracy by instruments onboard Earth-orbiting satellites, the stage is set for the development
of climate models with the potential of predicting future states of Earth’s global-scale climate
system. In addition to predicting future climate, these climate models can be manipulated
quantitatively (e.g., changing the atmospheric concentrations of heat-trapping gases) to
Climate Studies: Investigations Manual 3rd Edition
1B - 2
provide insight into the probable consequences of various human activities (e.g., combustion
of fossil fuels, land clearing).
In this course, the AMS Conceptual Energy Model (AMS CEM) will be employed to
investigate basic concepts underlying the global-scale flows of energy to and from Earth.
This investigation explores energy flow in a highly simplified representation of an imaginary
planet and the space environment above it. The purpose is to provide insight into the impacts
of physical processes that operate in the real world. This investigation follows the flow of
energy as it enters, resides in, and exits a planetary system model, as shown in Figure 1.
As seen in Figure 1 (a), short-wave solar energy is intercepted by the planet and absorbed
at its surface. In Figure 1 (b), the solar-heated surface emits long-wave infrared radiation
upwards. In the absence of an atmosphere, the upward-directed radiation would immediately
be lost to space. With a clear, cloud-free atmosphere added to the planet, as in Figure 1 (c),
some of the upward-directed radiating energy would be absorbed by molecules of heattrapping greenhouse gases (primarily H2O and CO2). The absorbed energy subsequently
radiates from the molecules to their surroundings randomly in all directions, with
essentially half of the emissions exhibiting a downward component and half an upward
component. While upward emissions can escape to space, the energy directed downward
can return to the planet’s surface and add to the amount of energy contained in the planetary
climate system.
Figure 1.
(a) Sunlight heats the surface of the planet. (b) In absence of an atmosphere, the surface emits
infrared radiation to space. (c) If there is an atmosphere, greenhouse gases absorb infrared radiation
emitted from the planet’s surface and then radiate the energy in all directions, with half directed
downward and half upward.
Climate Studies: Investigations Manual 3rd Edition
1B - 3
Starting the AMS CEM Investigation:
The AMS Conceptual Energy Model (AMS CEM) is a computer simulation designed to
enable you to track the paths that units of energy might follow as they enter, move through,
and exit an imaginary planetary system according to simple rules applied to different
scenarios. For simplicity, consider units of energy to be equivalent bundles or parcels of
energy. To access the interactive model, go to the course website and in the “Extras” section,
click on AMS Conceptual Energy Model. Then click on Run the AMS CEM.
As shown in Figure 2, the AMS CEM is presented as a landscape view of a planetary
surface, with the Sun depicted in the upper right corner. The AMS CEM is manipulated by
choosing different combinations of conditions via windows along the top of the view. Once
the conditions have been set, click Run to activate the AMS CEM.
Figure 2.
Landscape view of AMS CEM showing possible choices or settings to conduct model runs.
Become acquainted with the AMS CEM. Start by selecting “One Atmosphere” under
Atmospheres and “Energy: 100%” under Sun’s Energy (denoting the arrival of a fresh
unit of energy from the Sun during each cycle of play). Select “10 cycles” under Cycles
so a model run will be composed of 10 cycles of play. Select “Introductory” under Mode.
Finally, click on Run. Because the model is in the Introductory mode, you can observe the
same run repeatedly without the cycle patterns changing. You can also stop a run at any time
by clicking on Pause in the Run window, and then continue the run by clicking on Resume
in the same window. Note that each model run starts with one unit of energy already at the
Climate Studies: Investigations Manual 3rd Edition
1B - 4
planet’s surface. An atmosphere, if present, does not absorb any of the incoming sunlight
passing through it.
1. Repeating or stepping through the run specified above as many times as necessary, follow
the first energy unit that originated from the Sun. As it arrives at the planet’s surface,
the yellow energy unit changes to [(green)(blue)(red)]. This signifies its transition from
sunlight to heat energy as it is absorbed into the planet’s climate system.
In the AMS CEM, a cycle of play refers to a sequence of moves in which every energy unit in
the planet system is subjected to one vertical move. A model run is composed of a specified
number of cycles of play (i.e., 10, 50, 200). For example, a 10-cycle run of the model
indicates that whatever energy there is in the planetary climate system at the beginning of each
of the 10 cycles of play is subjected to one vertical-motion play during the individual cycle.
Once an energy unit is in the planet system, the two rules to be followed as it flows through
the planet system during each run of the AMS CEM are:
Rule 1. During each cycle of play, any energy unit at the planet’s surface will have an
equal chance of staying at the planet’s surface or moving upward.
Rule 2. During each cycle, any energy unit in the atmosphere will have an equal chance
of moving downward or upward.
These rules are primarily based on the fact that regardless the direction an energy unit
comes from when it is absorbed by an atmospheric molecule (i.e., CO2, H2O), the energy
emitted from the gas molecule can be in any direction. Half the emitted radiation will have a
downward component, and half an upward component.
2. Once an energy unit has been absorbed into the planet system, it continues to play
every remaining cycle in the run until it is either lost to space or is retained somewhere
in the planet system. Continue to follow the first energy unit that arrived from the
Sun by replaying the run as many times as you wish, or, by stepping through the run
by alternately clicking on Pause and Resume. In the cycle immediately following its
absorption at the planet’s surface, the energy unit being tracked
[(stays at the planet’s surface)(moves up to the atmosphere)].
3. In its next play, the same energy unit [(moves up to space)
(moves down to planet’s surface)].
4. Follow the same energy through the subsequent cycles of play. By the end of the 10-cycle
run, it [(remains in the planet system)(was lost to space)].
5. Next, follow the second energy unit to arrive from the Sun. After the cycle following its
arrival from the Sun, the second energy unit ends up [(at planet’s surface)
(in the atmosphere)(in space)].
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1B - 5
6. The planet’s climate system in the AMS CEM includes the planet’s surface and any
existing atmosphere. This Planet with an Atmosphere computer simulation, as with all
AMS CEM simulations, starts with one energy unit in the planet system at the planet’s
surface. After its 10 cycles of play, this particular run shows the planet system (surface
and atmosphere) ending up with [(1)(2)(4)(6)] units of energy.
Running this and other simulations in the Introductory Mode always produces the same
results for the individual simulation. This is because in the Introductory Mode all energy unit
movements are determined by the same set of random numbers essentially “frozen” for the
purposes of demonstrating how the model works. Random numbers are employed in AMS
CEM to assure that energy-unit movements are determined purely by chance. [In the Random
Mode a unique sequence of random numbers is generated with every run, so it is extremely
unlikely any two runs can be exactly alike and no run can be repeated.]
7. Modify the Mode setting for the AMS CEM simulation you have been examining (One
Atmosphere, Energy: 100%, 10 cycles) by clicking on “Random” under the Mode
heading. Now click on the Run button, and watch the model go through its 10-cycle run.
Play the new simulation several times, looking for similarities and/or differences. With
the random setting, different runs of the model produce [(different)(the same)] results.
The AMS CEM allows you to investigate numerous questions, such as what impact does
an atmosphere have on the amount of energy residing in the system. You can explore this
question by modifying the settings of the AMS CEM. Select “No Atmosphere”. The other
settings remain: Energy: 100%, 10 cycles, Random mode.
8. You have now changed the AMS CEM to evaluate a computer simulation of a Planet
with no Atmosphere. Click on the Run button and watch the model go through its
10-cycle run. Repeat several times. Comparison of several runs of the simulations with
and without an atmosphere, reveals the generalization that more energy is retained in the
planet system that [(has)(does not have)] an atmosphere.
9. Stated another way, comparing the two simulations (with and without an atmosphere)
shows that the addition of an atmosphere, containing energy-absorbing molecules, causes
the amount of energy in the planet’s climate system to [(increase)(remain the same)
(decrease)].
Now change the AMS CEM setting to: One Atmosphere, Energy: 100%, 10 cycles, and
Introductory mode. Click on the Run button to review the 10-cycle run. Then, sequentially,
choose and make “20”, “50”, and “100” cycle runs. Since the model is running in the
Introductory mode, each subsequent higher-cycle run embodies the previous lower-cycle
runs. Note that the model speeds up as the number of cycles in a run increases. This is
primarily done as a time-saving device when operating the AMS CEM.
Set the model to 200 cycles and click on the Run button. While it is running, note the
curves being drawn on the graph directly below the landscape view. This part of the model
Climate Studies: Investigations Manual 3rd Edition
1B - 6
is reporting (blue curve) the number of energy units in the planet system cycle-by-cycle as
the run progresses. It is also reporting a five-cycle running average (green curve). Running
averages are commonly calculated in climate science to even out short-term variations
and reveal trends. They are calculated at the end of each cycle by adding the most recent
observed value and dropping the oldest one. This averaging technique is especially useful in
the environmental sciences as new observational data are collected.
10.Directly above the graph, the model reports that for the 200-cycle run, the mean (average)
number of energy units in the planet system after each cycle was [(3.0)(4.7)(6.6)(8.2)].
The model starts a run with one energy unit in the planet system and the arrival of one energy
unit from the Sun. An initial “spin up” of the model occurs over ten to twenty cycles before
it appears to suggest the model has achieved a relatively stable condition. Although the
numbers of energy units in the planetary system can vary considerably over several cycles,
the long-term trend shows little evidence of either increasing or decreasing.
11. After an initial “spin up” of the model, the number of energy units in the planet system
during the Introductory-mode 200-cycle run ranged between [(0)(1)(3)(5)] and 8.
12.Even with the model settings being the same throughout the 200-cyce run, the energycontent curve displays variability about the mean. The overall pattern of the curve
suggests that the planet’s climate system (i.e., energy content) appears relatively stable.
Assuming such a “steady state” condition was achieved, it can be expected that the rate at
which energy is leaving the system to space would be [(less than)(equal to)(more than)]
the rate of incoming energy from space.
Keeping other settings the same, switch to the Random mode. Try several runs of the model
to see differences and similarities in results. Since the settings were kept the same, the
differences you observe, that is, differences in the means and departures from the means,
must be due exclusively to chance within the model’s operation. These can be referred to
as examples of natural variability as they cannot be attributed to any change in the system
settings (because there were no changes). That is, they were due to the inherent randomness
built into the rules on which the model is based.
We will return to the AMS CEM in future investigations to follow the flow of energy through
Earth’s climate system in different simulations under different sets of conditions. We will
then be observing evidence of climate change.
Earth’s Climate System Models
The purpose of the AMS CEM is to provide a tool enabling you to explore fundamental
aspects concerning energy flow to, through, and from Earth’s climate system. Climate system
models for scientific research and prediction are much more complex. They are mathematical
computer-based expressions of the conversions between heat and other forms of energy, fluid
motions, chemical reactions, and radiant energy transfer.
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The use of models to predict weather and investigate the Earth system and its climate
system was one of the most immediate results of the invention of the computer and rapid
development of computer technology beginning in the 1950s. NOAA’s Geophysical Fluid
Dynamics Laboratory (GFDL) at Princeton University created during the 1960s and 1970s
what was generally recognized as the first true Global Circulation Model (GCM) that
represented large scale atmospheric flow. It was at GFDL that the first climate change carbondioxide doubling experiments with GCMs were conducted.
Figure 3 schematically depicts the components, or sub-systems, of Earth’s climate system
(atmosphere, ocean, terrestrial and marine biospheres, cryosphere, and land surface) that
must be considered in advanced computer climate models. These major components interact
with each other through flows of energy in various forms, exchanges of water, the transfer of
greenhouse gases (e.g., carbon dioxide, methane), and the cycling of nutrients. Solar energy
is the originating source of the driving force for the motion of the atmosphere and ocean, heat
transport, cycling of water, and biological activity.
13.The arrows in the figure identify the processes and interactions with and between the
major components of Earth’s climate system. The double-headed arrows show that
[(almost all)(about half)(few)] of the processes and interactions between climate system
components (e.g., precipitation-evaporation, land-atmosphere) involve bi-directional
(upward/downward) flows.
Figure 3.
Schematic view of the components of Earth’s climate system, their processes and interactions. [IPCC
AR4 WG1 faq-1-2-fig-1]
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14.Six of the interactions depicted in Figure 2 are specifically labeled “Changes in …”
“Changes” imply forcing that results in climate change. While the human impact that
most impacts global climate is change in the atmosphere (composition), the human
impact most observably altering the local or regional climate is the one concerning the
[(ocean)(hydrological cycle)(cryosphere)(land surface)].
Summary: This Investigation has presented the AMS CEM, a simple conceptual model
that demonstrates climate as a planet system’s response to external forcing (radiant energy
from the Sun) and the amount of energy that is held in the system. It embodies some basic
elements of computer-based climate models which are representations of the climate system
based on the mathematical equations governing the behavior of the various components
of the system, including treatments of key physical processes, interactions, and feedback
phenomena.
EdGCM Project:
Computer-driven global climate models (GCMs) are prime tools used in climate research.
The Educational Global Climate Modeling Project provides a research-grade GCM, called
EdGCM, with a user-friendly interface that can be run on a desktop computer. Educators
and students can employ EdGCM to explore the subject of climate change the way research
scientists do. The model at the core of the EdGCM is based on NASA’s Goddard Institute for
Space Studies GCMs. To learn more about EdGCM, go to: http://edgcm.columbia.edu/.
Please note that the Internet addresses appearing in this Investigations Manual can be accessed
via the “Learning Files” section of the course website. Click on “Investigations Manual Web
Addresses.” Then, go to the appropriate investigation and click on the address link. We
recommend this approach for its convenience. It also enables AMS to update any website
addresses that were changed after this Investigations Manual was prepared.
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Investigation
2B:
Climate Variability and Change
Driving Question: What is climate change? Is there short-term evidence that human
activity can modify climate? How can we objectively determine
modification of climate due to human activity?
Educational Outcomes: To describe what is meant by climate variability and climate
change. To describe how human activities can significantly change one or more climate
measures, and how stopping particular human impacts might result in the climate measures
returning to their original states.
Objectives: After completing this investigation, you should be able to:
• Distinguish between climate variability and climate change.
• Describe one instance of climate change likely to be caused by human activity.
Materials: Red and blue pencils, ruler or other straight edge.
Climate Variability and Climate Change
Earth’s climate changes when the amount of energy contained in its climate system varies.
Determinations of whether or not Earth’s climate has changed, is changing, or is likely to
change are elusive tasks. While recognizing that the geological and historical record shows
an evolving climate, we face daunting challenges in our attempts to evaluate recent climate
trends (e.g., global temperature rise) and computer climate model products as evidence of shortterm variations in the climate or of persistent change in the climate system. When we study
climate, we must ask, “Are we observing statistical fluctuations of climate measures in a
steady climate state or are we witnessing real change in the mean climate state?” We can
start looking for answers to this question by defining what we mean by climate variability and
climate change. The more precisely we describe what we are looking for, the more likely we
will know when we find it.
Climate variability refers to variations about the mean state and other statistics (such as standard
deviation, statistics of extremes, etc.) of the climate on all time and space scales beyond that of
individual weather events [adapted from IPCC]. It is often used to describe deviations in climate
statistics over a period of time (e.g., month, season, year) compared to the long-term climate
statistics for the same time period. For example, a particular year’s average temperature will
very likely differ from the mean annual temperature for a recent 30-year period. Such variability
may be due to natural internal processes within the climate system or to variations in natural or
anthropogenic external forcing.
Climate change refers to any change in climate over time, whether due to natural forcing or as
a result of human activity [adapted from IPCC]. It refers to a significant change in the climatic
state as evidenced by the modification of the mean value or variability of one or more weather
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measures persisting over several decades or longer. Global climate change occurs ultimately
because of alterations in the planetary-scale energy balance between incoming solar
energy and outgoing heat energy (in the form of infrared radiation). The mechanisms that
shift the global energy balance result from a combination of changes in the incoming solar
radiation, changes in the amount of solar radiation scattered by the Earth system back to space,
and adjustments in the flow of infrared radiation from the Earth system to space, as well as
by changes in the climate system’s internal dynamics. Such mechanisms are termed climate
forcing mechanisms.
Climate change can occur on global, regional, and local scales. The prime (and most
pressing) example of climate change is global warming, recognized almost universally as
mostly due to increasing atmospheric carbon dioxide via burning of fossil fuels. Among
examples of anthropogenic climate forcing at a more regional level include changes in Earth’s
surface reflection of sunlight back to space due to land use and even the subtle impact of
aircraft contrails (as will be examined later in this investigation). Local climate data can provide
evidence of climate modification through human activity as seemingly innocuous as changes
in local farming practices. As you recall, the narrative section of the National Climatic Data
Center’s Local Climatic Data (LCD), Annual Summary for Grand Island, Nebraska, reports
that the increased use of irrigation and soil management techniques in local farming reduced the
frequency of dry season dust storms while increasing growing-season atmospheric humidities.
Determining Climate Variability and Climate Change
The scientific, objective investigation of climate and climate change requires the use of
clearly defined terms. We have already defined climate in terms of its empirical and dynamic
aspects.
We will use the term climate variability to describe the variations of the climate system
around a mean state (e.g., average temperature of a single month compared to the average
monthly temperature for that month as determined from several decades of observations).
Typically, the term is used when examining departures from a mean state determined by time
scales from several decades to millennia or longer.
The AMS CEM can be employed to illustrate climate variability. Go to the course website
and click on “AMS Conceptual Energy Model”. Then click Run the AMS CEM. Set the
model for one atmosphere, 100% Sun’s energy, 200 cycles, and Introductory mode, and click
on “Run”. The on-screen visualization includes, above the graph, the Mean and Standard
Deviation of energy units residing in the imaginary planet’s climate system (surface and
atmosphere) over the 200-cycle run. The graph displays curves drawn to report numbers of
energy units in the planetary system at the end of each cycle (jagged blue curve) as well as
the 5-cycle running mean (smoother green curve).
1. According to the CEM depicting the planet’s climate system and space above, at the end
of the 200th cycle there were [(4)(5)(6)] energy units residing in the climate system. Note
that this is the same value for the 200th cycle as depicted in the graph below the window.
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Figure 1 is an abridged version of the graph portion of the on-screen image that displays the
jagged blue curve reporting the number of energy units in the planetary climate system at the
end of each cycle.
Figure 1.
Energy units residing in Earth system over 200-cycle run of AMS CEM.
2. According to Figure 1, and ignoring the initial “spin up” of the model, the number of
energy units residing in the planetary climate system at the end of each cycle rose and fell
between [(1 and 7)(1 and 8)(2 and 9)]. The range (the largest minus the smallest in a set
of values) was 7. Range is a measure of variability.
3. In the on-screen image, note the mean number of energy units in the planetary climate
system for the 200 cycles as reported above the graph. On Figure 1, draw a solid
horizontal straight line representing that mean value of [(1.66)(3.2)(4.7)] energy units.
4. Shade with colored pencils the areas between the line depicting the mean and the jagged
blue curve. Color those areas above the mean red and those below the mean blue.
Visually, it should be apparent that the total shaded area above the mean line is equal to
the total shaded area below the mean line. The departures of the jagged curve from the
mean line represent the energy-unit variability of the system for that particular 200-cycle
run. A statistical measure of the magnitude of this variability is standard deviation (SD).
The greater the spread of observed values from the mean, the greater the SD. According
to the on-screen image, this 200-cycle run exhibits a SD of [(1.66)(3.2)(4.7)].
5. Draw on the Figure 1 graph horizontal dashed lines representing +1 SD (mean plus SD
value = 6.36) and –1 SD (mean minus SD value = 3.04) from the mean. Figure 2 shows
a plot of a normal distribution by SD (or σ). [A normal distribution is a frequency graph
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of a set of values, usually represented by a bell-shaped curve symmetrical about the
mean (μ).] According to the Figure 2 graph, [(4.1%)(68.2%)(95.4%)] of the observed
values fall between +1 SD and –1SD of the mean. On Figure 1, compare the shaded areas
between +1 SD and –1 SD with the total shaded area to confirm that this appears to be
correct.
Figure 2.
Normal Distribution by Standard Deviation (SD or σ – Greek letter Sigma) [Mwtoews, Wikipedia]
6. Draw horizontal dashed lines on Figure 1 representing +2 SD (mean plus 2 SD = 8.02)
and –2 SD (mean minus 2 SD = 1.38). Figure 2 shows that [(4.1%)(68.2%)(95.4%)] of
observed values can be expected to fall between +2 SD and –2SD. On Figure 1, compare
the shaded areas between +2 SD and –2 SD with the total shaded area to confirm that this
appears to be correct.
7. Figure 2 presents percentage values within SD intervals that show 4.4% of observed
values can be expected to have values greater than +2 SD or lower than –2 SD from
the mean. Your analysis of the Figure 1 curve [(does)(does not)] show observed values
beyond 2 SDs.
8. Because the CEM settings were kept the same throughout the 200-cycle run (one
atmosphere, 100% Sun’s energy), the variability observed [(is)(is not)] due to a change in
the system. So, it can be described as natural variability.
Climate Change?
Climate change, as used in this course, refers to any sustained change in the long-term
statistics of climate elements (such as temperature, precipitation or winds) lasting over
several decades or more, whether due to natural variability or as a result of human activity.
This definition follows the AMS Glossary of Meteorology, 2nd edition, 2000, and that used
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by the Intergovernmental Panel on Climate Change (IPCC). (While this course employs the
definition given here, keep in mind that climate change is defined by some to mean a change
of climate that can be attributed directly or indirectly to human activity only. The context in
which the term appears will usually inform the reader of the definition employed.)
9. Determining whether or not climate change has occurred requires comparison of
[(climate means)(climate variability)(both of these)] as determined from empirically
acquired climatic data for the same locality.
Return to the AMS CEM. Set the model for two atmospheres, 100% Sun’s energy, 200
cycles, and introductory mode, and click on “Run”. Only the atmosphere setting is different
from the AMS CEM scenario examined in the first part of this investigation when it was set
at one atmosphere. The two-atmosphere setting can be thought of as representing a doubling
of atmospheric CO2 compared to the one-atmosphere setting.
10.Compare this model product with that of the one-atmosphere model run. With two
atmospheres, the mean is [(2.36)(4.7)(10.7)] energy units. This higher mean, compared
to the one-atmosphere model run, suggests the doubling of the atmosphere has brought
about a sustained change in the planetary climate system, that is, it seems to exemplify
climate change.
11.The two-atmosphere model run produced a SD of [(2.36)(4.7)(10.7)].
Knowing the means, SDs, and numbers of cycles for the one- and two-atmosphere scenarios,
a statistical test can be applied to make a determination to some level of confidence that the
differences in the two model products are due to other than chance. The Student’s t-test
is commonly employed to make such a determination. Go to: http://www.graphpad.com/
quickcalcs/ttest1.cfm. To use this t-test calculator, in Step 1 click on the “Enter mean, SD
and N” button, in Step 2 enter under Group 1 one-atmosphere values of mean, SD, and N
(200) used earlier in this investigation, and under Group 2 enter the two-atmosphere values
of mean, SD, and N (200). After being sure “Unpaired t test” is selected in Step 3, click on
“Calculate now” in Step 4.
12.The Unpaired t test results that appear report a two-tailed P value of less than [(0.0001)
(0.001)(1.0)]. The P value is a probability, and can have a value ranging from zero to one.
The smaller the P value, the greater the probability that the difference between sample
means is due to something other than chance or coincidence. The smaller the P value,
the more confident you can be that the two samples you compared are from different
populations, that is, they are significantly different.
13.On the same Unpaired t test results page, the P value reported indicates the difference
between the means of the two samples is considered to be statistically [(not significant)
(significant)(extremely significant)].
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14.This indicates with a high level of confidence that the difference of the one-atmosphere
and two-atmosphere scenarios is due to some factor, not simply chance or coincidence.
We can therefore say or infer with a high level of confidence that the addition of a second
atmosphere (or doubling of CO2) resulted in [(no climate change)(climate change)].
Optional: To become more familiar with these basic statistics being applied to the AMS
CEM output, compare different pairs of runs of the model including using the “random”
mode and changing other settings (one at a time). Make the comparisons by calculating the t
test.
Aircraft Contrails, Cirrus Clouds, and Climate Variability and Change:
The advent of jet aircraft and the huge growth in air traffic after World War II resulted in an
increase in cirrus clouds formed by contrails from engine exhaust. A question of considerable
interest to atmospheric scientists has been whether or not the increase in contrails and related
cirrus clouds has impacted weather and climate. If the increase in contrails has impacted
climate, it is obviously an example of anthropogenic climate change. Figure 3 shows the
prevalence of contrails as well as indications that under certain conditions contrails seed a
more expansive cloud cover.
Figure 3.
NASA MODIS image of contrails over Midwestern U.S. [NASA] http://earthobservatory.nasa.gov/
IOTD/view.php?id=7161
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Aircraft contrails are clouds that form when hot jet engine exhaust containing considerable
quantities of water vapor (a combustion product) mixes with the cold high-altitude air. They
are the most visible anthropogenic atmospheric constituents in regions of the world with
heavy air traffic.
Because contrails and related cirrus clouds triggered by contrails reflect solar radiation
and absorb and emit infrared radiation, it is reasonable to expect that their persistence and
pervasiveness likely impact climate. They not only may be affecting climate at the current
time, but their impact can be expected to increase as it is projected that jet air traffic will
grow in the decades ahead.
A Possible “9-11” Climate Lesson
The date 11 September 2001, or simply “9/11,” marks one of the darkest days in our
country’s history. By 9:30 EDT on that morning, it became clear to officials at the Federal
Aviation Administration (FAA) that something was terribly wrong. One immediate response
to prevent the possibility of other aircraft being used as destructive weapons was the
remarkably quick national grounding of all commercial, military, and private aircraft. Within
an hour or so, the more than 4000 aircraft in U.S. airspace and international flights headed
to this country were directed to the airports nearest them. By the afternoon of 9/11, the only
contrails visible on satellite images were those coming from the President’s Air Force One
and its two fighter jet escorts on their way to Washington, DC.
U.S. skies remained essentially clear of aircraft for more than a day. In general, the grounding
remained in effect until 13 September. The grounding totally ended when Washington’s
Reagan National Airport finally opened on 4 October.
The 9/11 aviation shutdown gave scientists unique opportunities to study a few isolated
contrails developing without interference from neighboring contrails and to acquire evidence
of possible climate shifts. A study of particular significance to climate change was conducted
by Prof. David Travis (University of Wisconsin-Whitewater) comparing surface air
temperatures across the country during the aircraft grounding with those before 9/11.
The Travis analysis showed that during the absence of contrails (the 11-13 September time
period when skies were generally clear), the difference between the highest temperature
during the day and the lowest temperature at night increased 3 Fahrenheit degrees on
average and as much as 5 Fahrenheit degrees in areas of the country where contrails were
usually most common. This led Travis to conclude that contrails and related cirrus clouds
influenced climate by increasing the reflection of incoming solar radiation back to space
during the day, thereby reducing heating at Earth’s surface, and then absorbing some of the
upwelling infrared radiation from Earth’s surface at night. A considerable amount of the
absorbed radiation is emitted back towards Earth’s surface, where it has a heating effect.
Together, these two processes potentially reduce the diurnal (daily) temperature range. Travis
speculated that climatologically there is a net cooling effect because there are generally more
flights and contrails during the day than at night.
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15.Recalling the perspectives of climate as described in Investigation 1A, Prof. Travis’s
study of observed surface air temperatures across the country was essentially a(n)
[(dynamically)(empirically)] based investigation.
16.Because of the distribution of contrails as displayed in Figure 3, any climate change
brought on by the occurrence of contrails might best be described as [(regional)(global)]
in scale.
While Travis’s statistical treatment of climatic data in his study does show a greater
temperature range and a higher mean temperature when contrails were absent, it is not clear
that the evidence demonstrates unequivocally the impact of contrails on climate. A 2008
study, “Do contrails significantly reduce daily temperature range?” by Gang Hong et al,
Texas A&M University, reports that the increase of the average daily temperature over the
United States during the 11-14 September 2001 aircraft grounding period was within the
range of natural temperature variability observed from 1971 to 2001.
Hong’s study concluded that the missing contrails may have affected the daily temperature
range, but their impact is probably too small to detect to a level of statistical significance.
Hong showed that the diurnal temperature range is governed primarily by lower altitude
clouds, winds, and humidity. Specifically, the unusually clear and dry air masses covering
the Northeastern U.S. in the days following the terrorist attacks favored unusually large daily
temperature ranges.
Summary: The studies referred to in this investigation are presented to demonstrate
the challenges of identifying and discriminating between natural climate variability and
climate change. The AMS CEM was employed to illustrate climate variability and climate
change. Studies of the 11-14 September 2001 time period when contrails were temporarily
absent over the U.S. potentially provided a unique opportunity for detecting climate change,
if any, due to contrail impact. Careful studies of probable causes of unusually large daily
temperature ranges at the time ascribe whatever differences that were detected as explainable
within the range of natural variability of atmospheric conditions.
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Investigation
SOLAR ENERGY AND
EARTH’S CLIMATE SYSTEM
3A:
Driving Question: How does solar energy received by the Earth vary during the year at
different latitudes?
Educational Outcomes: To describe how the amount of solar radiation intercepted by
Earth varies at different latitudes over the period of a year. To learn how changes in the Sun’s
path through local skies impact the amount of incident solar radiation. To make comparisons
of how much solar radiation is received at tropical, midlatitude, and polar locations at
different times of the year. To estimate the impact of the atmosphere on incoming solar
radiation by comparing the amount received at Earth’s surface with that striking the top of
the atmosphere.
Objectives: As stated in Investigation 1A, climate can be thought of as the story of solar
energy intercepted by Earth being absorbed, scattered, reflected, stored, transformed, put to
work, and eventually emitted back to space as infrared radiation. The solar energy entering
the Earth system is the ultimate boundary condition of climate as the Sun is the source of
energy that heats Earth’s climate system.
After completing this investigation, you should be able to:
• Describe the variation of solar radiation received at the top of the atmosphere at
equatorial, midlatitude, and polar locations over the period of a year.
• Compare the amounts of solar radiation received at a midlatitude location at the top of the
atmosphere and at Earth’s surface under clear-sky and average conditions during different
times of the year.
Incoming Solar Radiation
Over the period of a year the amount of solar radiation received at Earth’s surface varies
considerably at most latitudes. This variation is governed largely by the boundary condition
arising from the changing paths of the Sun through the local sky, due to Earth rotating on
an axis inclined to the plane of its annual orbit about the Sun. These planetary motions
constantly change the part of Earth’s surface bathed by the Sun’s rays. Every latitude on the
globe has its own annual pattern of incident sunlight. These patterns are governed by the
shifting path of the Sun through the local sky and the lengths of daily periods of daylight.
These variations are primarily responsible for the unequal distribution of absorbed solar
energy from the equator to the poles that drives Earth’s climate system.
Figure 1 displays the approximate paths of the Sun through the local sky at (A) the equator,
(B) a middle latitude location in the Northern Hemisphere, and (C) the North Pole on the
first days of summer, fall, winter, and spring. The paths are continuously changing through
perpetual annual cycles. Among the variations by latitude, at the equator the periods of
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Mar 21
Sep 23
Jun 21
Dec 21
Jun 21
Mar 21
Sep 23
Dec 21
(A)
(C)
(B)
E
N
S
H or i
zon
Jun 21
E
W
N
S
Mar 21
Sep 23
W
Figure 1.
Path of Sun through the sky on the solstices and equinoxes at (A) the equator, (B) a middle latitude
location in the Northern Hemisphere, and (C) the North Pole.
daylight are a constant half-day throughout the year, while at the pole there is one period of
sunlight through the year that lasts continuously for six months.
At the top of the atmosphere when Earth is at its mean distance from the Sun, an average
of about two calories of solar energy per minute strikes a square centimeter (1.4 kilowatts
per square meter or 0.14 watt per square centimeter) of a flat surface oriented perpendicular
to the Sun’s rays. This average rate is called the solar constant. The rates at which solar
energy penetrating the atmosphere actually strikes Earth’s surface are quite different and
highly variable. At any instant, the only point at which the Sun’s rays are perpendicular to
Earth’s surface is where the Sun is in the zenith. That sub-solar point races steadily around
the planet once a day as it follows an annual path that spirals between 23.5 degrees North and
23.5 degrees South latitudes. Twice a year, on the vernal and autumnal equinoxes, the Sun is
positioned directly above the equator. During the time between the vernal and the succeeding
autumnal equinox the sub-solar point is located in the Northern Hemisphere, while from the
autumnal to the following vernal equinox, the sub-solar point is positioned in the Southern
Hemisphere. The solstices occur when the sub-solar point reaches its maximum latitude
positions (23.5º N on the first day of the Northern Hemisphere’s summer in late June and
23.5º S on the first day of our winter in late December).
The Earth, spinning on an axis inclined 23.5 degrees from a line perpendicular to the plane
of its orbit, presents an ever changing face to the Sun. Wherever daylight occurs, the path
of the Sun through the local sky changes from day to day. Except at the equator, or at high
latitudes when there are days of continuous daylight or darkness, the daily length of daylight
also changes. Clouds, air molecules, and aerosols (tiny particles suspended in air) reduce
the amount of solar radiation reaching Earth’s surface. Some solar radiation is absorbed by
atmospheric components and some is scattered or reflected back to space.
Because absorbed solar radiation is the fundamental driver of Earth’s climate system, the
purpose of this activity is to investigate the variability of solar radiation received at the top of
the atmosphere and at Earth’s surface at different latitudes over the period of a year.
The great variation in the solar radiation received at different latitudes throughout a year is
primarily responsible for the temperature contrasts that result in the fluid parts of the Earth
system (atmosphere and ocean) transporting huge quantities of heat energy from lower
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to higher latitudes. These energy flows accompany the weather patterns and temperature
variations that characterize the seasons.
Effects of Latitude on Incoming Solar Radiation
What impacts do latitude and the atmosphere have on incoming solar radiation? NASA
provides monthly averaged top-of-atmosphere insolation values as well as those incident on
a horizontal surface at Earth’s surface for any global location (http://eosweb.larc.nasa.gov/
cgi-bin/sse/sizer.cgi?email=na). The term insolation is short for incoming solar radiation.
The top-of-atmosphere values would be the amount received at Earth’s surface if there were
no atmosphere. The NASA data report incident solar radiation in units of kilowatt hours per
square meter per day (kWh/m2/day). [For conversion purposes, 1 cal/cm2 = 0.01 kWh/m2.]
Figure 1(A) shows daily paths of the Sun at an equatorial location on the solstices and
equinoxes. Figure 2 displays a red curve that depicts the daily average solar radiation
striking a horizontal surface at the top of the atmosphere over a location on the equator
(0º Latitude). Data of average daily values for each month are plotted at mid-month. Draw
and label straight vertical lines on Figure 2 on the approximate dates of the Northern
Hemisphere’s vernal equinox (21 March), summer solstice (21 June), autumnal equinox (23
September), and winter solstice (21 December).
Figure 2.
NASA-generated average monthly top-of-atmosphere solar radiation (in kWh/m2/day) at equator (Eq),
midlatitude (ML), and North Pole (NP).
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1. Note the two maxima and two minima portions of the Figure 2 equatorial insolation curve
over the period of a year. Figure 2 shows that the minimum portions of average daily
solar radiation values at the top of the atmosphere over the period of a year occur during
the months of [(March and September/October)(June and December)]. These occur
when the sub-solar point is at its highest latitudes for the year, as seen in Figure 1(A).
2. The equatorial top-of-atmosphere curve in Figure 2 shows that the two insolation maxima
occur near the times of the [(solstices)(equinoxes)]. Because places on the equator
experience essentially the same period of daylight (approximately 12 hours) every day of
the year, the changes in the top-of-atmosphere radiation values over the year must be due
primarily to changes in the path of the Sun through the local sky (that is, changes in the
maximum daily altitude of the Sun). Note that the top-of-atmosphere insolation values
do not vary greatly over the year at the equator, with the minimum insolation value being
about 90% of the maximum insolation value.
3. Figure 1(C) describes Sun’s path through the local sky at the North Pole (90ºN) on the
summer solstice and the equinoxes. It shows that on these days, the Sun is on or above
the horizon for [(0)(12)(24)] hours. It can be inferred from the drawing that the Sun is
below the local horizon continuously from the fall equinox to the next spring equinox
(assuming no atmospheric effects).
4. Plotted on Figure 2 are data points (▲) of monthly average daily top-of-atmosphere
insolation at the North Pole (90º N). Assuming top-of-atmosphere insolation is zero on
the equinoxes, connect the adjacent values by drawing a smoothed curve (with a blue
pencil if available). The curve shows the North Pole receives essentially no incoming
sunlight for [(0)(3)(6)(9)(12)] months a year. (The insolation pattern at the South Pole is
similar except six months out of phase with that at the North Pole.)
5. Plotted on Figure 2 are data points (■) of monthly average daily top-of-atmosphere
insolation at 45 degrees North Latitude (45º N). Connect the adjacent values by drawing a
smoothed curve (with a green pencil if available). The midlatitude curve makes it evident
that the maximum insolation occurs on the summer solstice and minimum insolation
occurs on the winter solstice. It can be determined from Figure 2 that on an average day
in December the midlatitude location receives about [(25%)(50%)(75%)(100%)] of the
top-of-atmosphere insolation it receives on an average June day.
6. The midlatitude curve is characterized by having one maximum value and one minimum
value per year. Comparison of the curves now appearing on Figure 2 shows that the
midlatitude location [(always)(sometimes)(never)] receives top-of-atmosphere insolation
that is greater than what is received at the equator.
7. Figure 1(B) depicts Sun’s paths through the midlatitude local sky on the solstices and
equinoxes. The solstice paths demonstrate that changes in [(Sun’s maximum altitude)
(length of Sun’s path)(both of these)] contribute to the midlatitude’s annual range of
daily insolation.
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8. Comparisons of the three top-of-atmosphere curves drawn in Figure 2 demonstrate why
latitude is considered as a fundamental control of climate. The insolation values over the
period of a year vary the most at the [(equatorial)(midlatitude)(polar)] location.
9. The [(equatorial)(midlatitude)(polar)] location experiences the least change in
insolation, over the period of a year.
10.The three top-of-atmosphere insolation curves in Figure 2 indicate that during the
year, the most intense daily insolation occurs at the [(equatorial)(midlatitude)(polar)]
location.
Impacts of the Atmosphere on Incoming Solar Radiation
The rate at which solar energy is received at the top of the atmosphere is the fundamental
boundary condition of Earth’s climate system. Figure 3 is presented to demonstrate the
impact of the atmosphere on the sunlight entering the Earth system at a 45ºN location (Salem,
Oregon). The red curve drawn on the figure represents the same top-of-atmosphere insolation
data for 45º N as seen in Figure 2.
11.The blue data points (■) plotted on Figure 3 are calculated average monthly values of
daily insolation received at Earth’s surface at a 45º N location that would be observed
under clear-sky conditions (no clouds). Create the annual clear-sky insolation curve by
drawing a smooth curve through the data points (using a blue pencil if available). The
figure shows that during the month of May, 10.9 kWh/m2 of energy was received at the
top of the atmosphere. The figure also shows that under continuous clear-sky conditions,
it would receive about [(4.1)(6.1)(8.1)] kWh/m2 on an average May day.
12.The May data shows that for that month about [(26%)(41%)(76%)] of the solar energy
striking the top of the atmosphere is blocked by the clear atmosphere. This attenuation
(loss) is due to solar radiation being absorbed by atmospheric gas molecules (H2O and
O3) and particulates (dust) and by backscattering to space. Evaluation of the Figure 3 data
for all 12 months produce about the same result. Global energy budget studies place the
worldwide average for clear-air absorption and backscatter at about the same (actually,
about 2% less).
13.The green data points (▲) plotted on Figure 3 are calculated average monthly values of
daily insolation received at Earth’s surface at a 45º N location that would be observed
under average conditions (including clouds). Create the annual average surface insolation
curve by drawing a smooth curve through the data points (using a green pencil if
available). According to Figure 3, the May value for solar energy actually arriving at
Earth’s surface is [(4.1)(5.1)(8.1)] kWh/m2 for an average day.
14.Compared with the May top-of-atmosphere value, it shows that the actual atmosphere
(including clouds) blocks about [(37%)(53%)(76%) of the solar energy entering Earth’s
atmosphere at Salem, OR.
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Figure 3.
NASA-generated daily averaged top-of-atmosphere, clear-sky and surface incident solar radiation
data at Salem, OR, 45° N (in kWh/m2/day).
Global energy budget studies place the worldwide average for actual atmospheric absorption
and backscatter conditions (including clouds) at near, but slightly less than, the Salem, OR,
May value as reported in Figure 3. Figure 3 shows that the differences between Salem’s
May top-of-atmosphere and clear-sky values (2.8 kWh/m2/day) and the difference between
clear-sky and actual surface insolation values (3.0 kWh/m2/day) are nearly equal. This infers
that clear air and cloudiness are both major factors in determining how much of the solar
radiation arriving at the top of Earth’s atmosphere is attenuated before reaching the surface.
15.Actual surface insolation data reported in Figure 3 shows that monthly average values at
Salem, OR range from 1.1 kWh/m2/day in December to [(4.1)(5.1)(6.2)] kWh/m2/day in
July.
16.The actual surface insolation curve in Figure 3 demonstrates the wide swing in the
amount of solar radiation arriving at Earth’s surface at a midlatitude location over the
period of a year. According to the data in the previous item, Earth’s surface at Salem
receives on an average July day about [(2.1)(4.1)(5.6)] times as much solar energy as on
an average December day.
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Summary: The story of climate starts with Earth’s interception of solar radiation. The
amount of sunlight intercepted varies considerably by latitude and time of year. The amount
that reaches Earth’s surface is determined by astronomical factors (e.g., solar constant,
spherical Earth, rotation) and attenuation by atmospheric effects (e.g., cloudiness, absorption,
scattering). Incident solar radiation at a particular location has climate implications resulting
from the magnitude, path of the Sun through the daytime sky, and duration of daylight.
The solar energy entering the Earth system is the ultimate boundary condition of climate as
the Sun is essentially the only source of energy that heats the Earth system – particularly its
land and water surfaces and atmosphere. The amount of solar radiation received at Earth’s
surface varies considerably at most latitudes over the period of a year, setting the stage for
annual climate swings. Although solar energy is essential in fueling the climate system, the
Sun’s energy intercepted by Earth is only the beginning of the story of climate.
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Climate Studies: Investigations Manual 3rd Edition
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Investigation
5A:
Global Water Cycle
Driving Question: How does the global water cycle link the principal components of the
Earth system?
Educational Outcomes: To describe how unique properties of water place it in a major
role establishing the boundary conditions and variability of climate. To explain how water
cycles throughout the Earth system and impacts climate on all spatial and time scales, as
well as how it transports heat globally as part of the never-ending drive towards a uniform
distribution of energy.
Objectives: In the holistic Earth system perspective, Earth is composed of many
interacting subsystems including the atmosphere, geosphere, hydrosphere, cryosphere, and
biosphere. Earth’s climate system encompasses aspects of these same components because
their mutual interactions and responses to external influences determine climate on local,
regional, and global scales.
After completing this investigation, you should be able to:
• Describe the components of the global water cycle within Earth’s climate system.
• Explain ways in which the global water cycle links the various subsystems of Earth’s
climate system through flows of mass and energy.
• Explain the steady-state global water budget with more precipitation than evaporation
occurring over land and more evaporation than precipitation taking place over ocean
being balanced by the excess water on land dripping, seeping, and flowing back to sea.
The Global Water Cycle
In this investigation, some of the roles of water in shaping climate are explored, particularly
as water participates in the complex redistribution of energy and mass by Earth’s coupled
atmosphere/ocean system.
Figure 1 is a depiction of the water cycle in terms of mass and mass flows between oceanic,
terrestrial, atmospheric, and biospheric reservoirs. It provides a view of the water cycle
already familiar to most people. What it does not display is the essential reason why water
cycles through its reservoirs, namely, the accompanying energy flow. The mass flow of
water as portrayed in the figure is basically a response to the non-uniform distribution
of energy in the Earth system. Water’s coexistence in three different phases, its high
specific heat and latent heats, and the relative ease with which it changes phase within the
temperature and pressure ranges on Earth, makes it the working fluid that absorbs, transports,
and releases heat within the Earth system.
Water is the primary mover of energy from where there is relatively too much energy,
to where there is too little energy. Winds transport water vapor to every location on
Earth, including the highest mountain peaks. Changing back to liquid or solid within the
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Figure 1.
The Water Cycle [USGS]
atmosphere, water begins its gravity-driven return trip to Earth’s surface and eventually flows
into the ocean. Ocean currents also transport energy as warm waters flow to higher latitudes
and cold waters to lower latitudes. Development of a more complete and authentic depiction
of the global water cycle, including both mass and energy flows, is an integral part of Earth’s
climate system.
Water flow in the atmosphere is the essential heat-driven uphill component of the water cycle
that lifts water as vapor to great altitudes and transports it around the globe. The atmospheric
water vapor flow embodied in the water cycle is invisible to our eyes because water vapor
is transparent. However, special infrared sensors aboard weather satellites can detect the
presence of water vapor (and clouds) in the atmosphere above altitudes of about 3000 m
(10,000 ft).
You can view an animation of real Earth perspective full-disk GOES East
water vapor imagery for the last day at: http://www.ssec.wisc.edu/data/geo/
index.php?satellite=east&channel=vis&coverage=fd&file=jpg&imgoranim
=8&anim_method=jsani. At the SSEC Geostationary Satellite Images site,
click on Imager Channel: Water Vapor 6.5 μm to view the most recent fulldisk atmospheric water vapor.
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To examine an animated full global composite view covering the past week, go to:
http://www.ssec.wisc.edu/data/comp/wv/wvmoll.mpg.
In the atmospheric water vapor imagery bright white patches represent the relatively cold
tops of high clouds. Clouds occur where there are significant upward atmospheric motions.
Medium gray regions depict mainly water vapor. These gray regions would probably
appear clear on visible and ordinary infrared satellite images. Streaks and whirls of gray are
common patterns in the water vapor images at the middle and higher latitudes. Dark areas are
relatively dry portions of the middle atmosphere resulting from the sinking of low humidity
air from higher altitudes.
1. Viewed in animation, the cloud patterns in the tropics and the curving swirls of water
vapor in middle latitudes of the Northern and Southern Hemisphere portions of the
images reveal that atmospheric motions [(do)(do not)] transport water vapor horizontally
over great distances within the atmosphere.
2. Examine the general motion in the middle latitudes of the Northern and Southern
Hemispheres. [To better analyze motions, consider using the control button to step
forward through successive images.] In the middle latitudes, the dominant horizontal
motion in both hemispheres is from [(higher to lower latitude)(east to west)
(west to east)].
3. Examine the motion seen in the tropical latitudes. The numerous bright white cloud
patches at these latitudes signify upward convection currents and thunderstorms. These
tropical clouds embedded in air with relatively high water vapor concentrations generally
mark the Intertropical Convergence Zone (ITCZ). Here, intense solar energy arriving
at Earth’s surface heats near-surface air, promoting evaporation (and transpiration,
especially in tropical rainforests) and upward vertical motions. The dominant horizontal
motion in the ITCZ is from [(east to west)(west to east)].
Figure 2 displays two composite images acquired one day apart. The upper image is
from 0000 UTC 27 DEC 2011 (7:00 pm EST on the 26th) and the lower image is 24 hours
later, 0000 UTC 28 DEC 2011. During this time period a winter storm system delivering
considerable precipitation traveled up the U.S. East Coast packing strong winds that downed
trees and power lines leading to delays in post-holiday travel.
4. Note on the upper image the broad band of light gray extending from the tropical Pacific
Ocean across central Mexico to the Southeastern states. The brightest area in that band
centered northwest of Florida corresponds to the major winter storm that brought high
winds and heavy rains across a broad area of the country while traveling up the East
Coast. Such midlatitude swirls are storm systems that transport warm humid air poleward
to be replaced by colder drier polar air moving equatorward. Such storm motions transfer
[(water mass)(heat energy)(both)] within the Earth system.
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Figure 2.
Composite satellite images displaying the distribution of water vapor in the middle levels of the
atmosphere at 0000 UTC 27 December 2011 (upper view) and 0000 UTC 28 December 2011 (lower
view). The lower view has lines signifying the positions of the equator (green) and average December
position of the Intertropical Convergence Zone (ITCZ) in yellow. [SSEC-UW]
5. Based on what you learned about midlatitude atmospheric motions (generally west
to east) from the animated images, it appears that the plume of water vapor fueling
the winter storm system described above originated primarily (upper image) from the
Climate Studies: Investigations Manual 3rd Edition
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[(Pacific Ocean)(Atlantic Ocean)]. It is evident from a global water cycle perspective,
that water evaporated from ocean surfaces was incorporated in the overlying air and
transported to areas above land surfaces where significant quantities then precipitated
as rain, freezing rain (icing), and snow.
6. Now examine the lower image in Figure 2 showing atmospheric water vapor distribution
one day after the upper image. Focus in on the U.S. East Coast area. It is evident from the
two images that the winter storm had moved generally towards the [(east)(west)]. This
movement, combined with north or south components, is commonly characteristic of
midlatitude storm systems. The patterns and frequency of such storm systems have major
impacts on local and regional climate at places in their paths.
7. A straight green line has been drawn across the midsection of the lower image in
Figure 2 to represent the equator. The yellow curve approximates the center of the
average December position of the Intertropical Convergence Zone (ITCZ). The ITCZ
is a relatively narrow, irregular band of convective clouds and thunderstorms roughly
parallel to the equator in which huge quantities of water vapor enter the atmosphere from
underlying warm surface ocean waters and tropical rainforests (e.g., Amazon Basin).
Note the general agreement between the brightest clouds surrounded by light gray
shadings and the average December ITCZ position. They show that at this time of the
year the ITCZ is largely [(north)(south)] of the equator. Six months later, the ITCZ is
found almost entirely on the opposite side of the equator.
8. In Figure 2, two darker irregular bands surrounding Earth and located north and south
of the equator indicate the presence of [(dry)(humid)] air. These are broad regions of
relatively high surface air pressure and associated sinking air which produce relatively
persistent clear skies and fair-weather conditions, which in turn have major impacts on
local and regional climates.
9. The flow of atmospheric water vapor is a major energy transport mechanism in Earth’s
climate system. The energy flow starts with the evaporation of water from ocean and land
surfaces or transpiration by vegetation transferring energy
[(from air to water and land surfaces or vegetation)
(from water and land surfaces or vegetation to air)].
10.Atmospheric water vapor is often carried great distances before it condenses to liquid
or solid cloud particles, thereby transporting huge quantities of [(sensible)(latent)] heat
energy from one place to another.
11.Assume that much of the heat energy added to the environment by the late December
2011 Southeastern U.S. winter storm depicted in Figure 2 was carried in the water
vapor plume shown flowing generally northeastward into the storm. The heat energy
carried by the plume in the lower image was now originating most directly from the
[(Pacific Ocean)(Atlantic Ocean)]. In combination with Item 5, it is evident that the
global water cycle embodies both mass and energy flow.
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The global water cycle’s transport of mass (and, indirectly, energy) can be traced via NASA’s
Tropical Rainfall Measuring Mission’s (TRMM) rainfall animations. TRMM provides
estimates of rainfall between about 40 degrees N and 40 degrees S using sensors on a
satellite.
Go to: http://trmm.gsfc.nasa.gov/publications_dir/global.html (QR Code)
and click on A WEEK of Rainfall “Medium Quicktime” or “Medium Mpeg” to
observe rainfall patterns for the previous seven days.
12.The TRMM Rainfall patterns during the past week, when generalized, show evidence of
[(passage of storm systems from ocean to land and from land to ocean)
(general eastward motion of midlatitude storms)
(general westward motion of tropical storms)(all of these)].
At the same NASA TRMM website, click on A WEEK of Rainfall ACCUMULATION
“Medium Quicktime” or “Medium Mpeg” to observe accumulated rainfall patterns for the
previous seven days.
13.Broad areas in the TRMM global accumulated rainfall pattern for the past week that
exhibited evidence of little or no rainfall generally [(show no relationship to)
(coincide with)] the dark areas in the animated global views of atmospheric water vapor
you viewed at the beginning of this investigation. As you recall, the dark areas denoted
low water vapor content.
Summary: Water cycles throughout the Earth system. Water vapor flow in the atmosphere
is the essential heat-driven uphill component of the water cycle that lifts water as vapor to
great altitudes and transports it around the globe. The atmospheric energy flow embodied in
the water cycle is largely invisible to our eyes but special infrared sensors aboard weather
satellites enable us to monitor it. The atmosphere delivers water vapor globally and impacts
climate on all spatial and time scales, acting as a major agent transporting heat in a neverending drive towards a more uniform distribution of energy.
Climate Studies: Investigations Manual 3rd Edition
Investigation
9B:
9B - 1
methane Hydrates:
major implications FOR CLIMATE
Driving Questions: What are methane hydrates? What role might methane hydrates
have played in causing the PETM (Paleocene-Eocene Thermal
Maximum) and what were the possible impacts on atmospheric
and ocean carbon dioxide levels? Are there similarities between
PETM and current anthropogenic loading of carbon dioxide in the
atmosphere and ocean?
Educational Outcomes: To describe methane hydrates and how they can impact
concentrations of carbon dioxide in the atmosphere and ocean. To examine any similarities
between what happened during the PETM and the current upward trends in atmospheric and
oceanic carbon dioxide.
Objectives: After completing this investigation, you should be able to:
• Describe the chemical and physical characteristics of methane hydrate and its distribution
in the Earth environment.
• Demonstrate how methane hydrates could be major sources of atmospheric and oceanic
carbon dioxide.
• Compare possible similarities in the role of methane hydrates in atmospheric and oceanic
carbon dioxide concentrations during PETM and modern climate change.
PETM and Methane Hydrates
The PETM, the abrupt warming of Earth’s atmosphere and ocean and associated
environmental impacts that occurred about 55.8 million years ago, was global in scale
and its impact lasted for more than 100,000 years. It was likely triggered by the rapid
emission of carbon dioxide (CO2), or by methane (CH4), which chemically reacts with
oxygen to produce CO2 (and water). Possible sources of the huge amount of carbon that
was necessary for producing the PETM are not known with certainty. It could have been
from the release of methane (CH4) from decomposition of hydrate deposits in seafloor
sediments, CO2 from volcanic activity, and/or oxidation of organic-rich sediments. There is
considerable scientific evidence pointing to the possibility that the release of methane from
naturally occurring solid methane hydrate deposits in ocean sediments played a prime role
in producing the PETM.
Figure 1 shows a sample of methane
hydrate. If ignited in air, it burns, as seen
in the image. Up to 170 volumes of CH4
as a gas at 1 atmosphere of pressure can be
contained in one volume of methane hydrate.
Methane hydrate (also called methane
clathrate and methane ice) belongs to a
Figure 1. Burning methane hydrate. [National
Research Council of
Canada, NRC-SIMS]
Climate Studies: Investigations Manual 3rd Edition
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unique class of chemical substances composed of molecules of one material forming an open
solid crystal lattice that encloses, without chemical bonding, molecules of another material as
represented in Figure 2. Methane hydrate is a solid form of H2O that contains methane (CH4)
molecules within its crystal structure. It is the inclusion of sufficient methane molecules within
the open cavities between water molecules that causes the stable solid structure to form (i.e.,
methane hydrate).
Figure 2.
Methane hydrate is a solid substance in which water molecules form an open crystalline lattice
enclosing molecules of methane. [National Energy Technology Laboratory, DOE]
1. In Figure 2, the central molecule represents four (gray) hydrogen atoms bonded to a
(yellow) [(oxygen)(carbon)] atom. The surrounding water molecules form the crystal lattice
that makes the substance solid.
Within certain pressure and temperature ranges, methane hydrates form and remain stable in the
Earth environment. To view methane hydrate formation and outcrops on the seafloor of the Gulf
of Mexico and to answer the following questions, go to: http://2100science.com/Videos/Frozen_
Fuel.aspx. Click on the arrowhead in the middle of the YouTube screen to start the program.
2. Early in the 8-minute video and again at about 7:40 minutes into the video you can view
the burning of methane hydrate. A scientific error was made in the video narration with
the statement that “methane hydrate is frozen methane.” Evidence that this statement is
probably not true is the [(absence)(presence)] of liquid water that can be seen as the burning
of methane hydrate takes place. The flames seen result from the combustion of CH4. The
loss of CH4 molecules leads to the collapse of the crystal lattices formed by the water
molecules, so solid turns to liquid.
3. According to the narration (described at about 3:55), the actual seafloor observations in this
video were made at a depth of [(1200)(2100)(2900)] feet.
4. The actual formation of methane hydrate can be seen in the video starting at about 4:50. The
CH4 entering the sampling tube in which the methane hydrate forms is in its [(liquid)(solid)
(gas)] phase.
Climate Studies: Investigations Manual 3rd Edition
9B - 3
5. Methane hydrate outcrops can be viewed starting at 6:10. The existence of such outcrops
is strong evidence that methane hydrate is [(stable)(unstable)] at the pressures and
temperatures at that seafloor location.
Figure 3 is a methane hydrate phase diagram showing the combination of temperatures and
pressures (given as water depth in meters). In the diagram “water-ice” refers to ordinary ice.
Enclosed in the yellow area are combinations of temperature and pressure at which (solid)
methane hydrate can stably exist.
6. The solid line between yellow and blue portions of the phase diagram marks the transition
between conditions under which methane hydrate can or cannot exist. It indicates that at
sufficiently high pressures, methane hydrate can exist at temperatures above the melting
point of ordinary ice. At about 880 m (the depth of the Gulf of Mexico seafloor where the
methane hydrate outcrops were observed in the above video), the temperature could have
been as high as [(+8 °C)(+10 °C)(+12 °C)].
7. The phase diagram also shows that methane hydrate can exist at relatively shallow depths.
At a temperature of 0 °C, methane hydrate could exist at water depths as shallow as about
[(300 m)(400 m)(500 m)].
Figure 3.
Methane Hydrate Phase
Diagram denoting depth (i.e.,
pressure) and temperature at
which methane hydrate can
exist. Methane hydrate is a solid.
[National Energy Technology
Laboratory, DOE]
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9B - 4
It should be noted that the Figure 3 phase diagram is based on interactions of pure substances.
In addition to temperature and pressure, the composition of both the water and the gas are
critically important when making predictions of the stability of methane hydrates in different
environments.
Methane Hydrates and the 2010 Gulf of Mexico Deepwater Oil Spill:
In the Deepwater Horizon oil spill catastrophe, methane hydrate was at least implicated as the
possible source of the methane gas that likely caused the explosion and fire that destroyed the
Deepwater Horizon oil drilling platform. In the initial clean-up efforts, it was unquestionably
identified as responsible for thwarting the futile attempt of BP engineers to deploy an oil
containment dome, acting as an upside-down funnel, to capture escaping oil and piping it to a
storage vessel on the surface.
An oil containment dome was deployed on May 7-8 as one of the early attempts to cap the flow
of escaping oil and natural gas (primarily composed of CH4 ). It failed because the relatively low
density methane hydrate that formed produced a slush that made the dome buoyant while at the
same time clogging the pipe exiting at the dome’s top.
8. The Figure 3 phase diagram shows why methane hydrate formed when methane and water
mixed inside the containment dome. This can be seen by plotting a point on the phase
diagram at a depth of 1500 m and temperature of 5.5 ºC, representing the conditions at the
seafloor well site. The plot falls within the [(blue)(yellow)] portion of the phase diagram
indicating stable conditions for the existence of methane hydrate.
Methane Hydrates and PETM: Because the temperature and pressure ranges at which
methane hydrates can exist are found throughout much of Earth’s subsurface environment,
it carries with it great potential to impact climate. This was as true in the past as it is now.
As mentioned earlier, there is strong evidence that the release of CH4 from methane hydrates
might have been the primary forcing agent producing the PETM. This possibility has been
thoroughly treated in learning materials developed by the Deep Earth Academy at: http://www.
oceanleadership.org/wp-content/uploads/2009/06/8_petm_abrupt-events.pdf. We recommend
that you examine the materials.
Global Distribution of Methane Hydrates: Figure 4 describes the distribution
of organic carbon in various Earth reservoirs. Gas hydrates are primarily methane hydrates,
although other molecules of similar size to CH4 (including hydrogen sulfide, carbon dioxide,
ethane, and propane) form gas hydrates.
9. The one organic carbon reservoir greater than all the other reservoirs combined is
[(the ocean)(fossil fuels)(the land)(atmosphere)(gas hydrates)].
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Figure 4.
Earth reservoirs of organic carbon.
[http://marine.usgs.gov/fact-sheets/gas-hydrates/gas-hydrates-3.gif]
Summary: Figure 5 summarizes major aspects of methane hydrates in the Earth
environment.
10. Figure 5 shows the two sources of the methane that are incorporated in the methane hydrate
deposits. Biogenic generated CH4 gas is the common by-product of bacterial ingestion of
organic matter. It is considered to be the dominant source of the methane hydrate layers
within shallow sea floor sediments. [(Hydrogenic)(Cryogenic)(Thermogenic)] generated
CH4 gas is produced by the combined action of heat, pressure and time on deep-buried
organic material that also produces petroleum.
While not discussed here, large deposits of methane hydrates also occur in permafrost. With
global warming and associated thawing of vast frozen land areas, the expectation is that
significant quantities of CH4 will be released. Their oxidation will lead to additional CO2,
enhancing the greenhouse effect.
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9B - 6
Figure 5.
Types of gas (mostly methane) hydrate deposits. [U.S. National Energy Technology Laboratory
(NETL) http://204.154.137.14/technologies/oil-gas/FutureSupply/MethaneHydrates/about-hydrates/
geology.htm]
Climate Studies: Investigations Manual 3rd Edition
AMS Clim at e S t u d i e s
Introduction to Climate Science
Invest i g at i o n s
M a nu al
Edition 3
The American Meteorological Society
Education Program
The American Meteorological Society (AMS), founded in 1919, is a scientific and professional society.
Interdisciplinary in its scope, the Society actively promotes the development and dissemination of information on
the atmospheric and related oceanic and hydrologic sciences. AMS has more than 15,000 professional members from
more than 110 countries and over 175 corporate and institutional members representing 40 countries.
The Education Program is the initiative of the American Meteorological Society fostering the teaching of the
atmospheric and related oceanic and hydrologic sciences at the precollege level and in community college, college
and university programs. It is a unique partnership between scientists and educators at all levels with the ultimate
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public scientific literacy. This is done via the development and dissemination of scientifically authentic, up‑to‑date,
and instructionally sound learning and resource materials for teachers and students.
AMS Climate Studies, the newest component of the AMS education initiative, is an introductory undergraduate Climate
Science course offered partially via the Internet in partnership with college and university faculty. AMS Climate
Studies provides students with a comprehensive study of the principles of Climate Science while simultaneously
providing classroom and laboratory applications focused on the rapidly evolving interdisciplinary field of Climate
Science.
Developmental work for AMS Climate Studies and the companion DataStreme: Earth’s Climate
System was supported by the National Aeronautics and Space Administration under Grants Number
NNX09AP58G and NNX08AN53G. Any opinions, findings, and conclusions or recommendations
expressed in this material are those of the author and do not necessarily reflect the views of the National
Aeronautics and Space Administration.
Climate Studies Investigations Manual 2011 - 2012 and Summer 2012
ISBN-10: 1-935704-99-0
ISBN-13: 978-1-935704-99-7
Copyright © 2012 by the American Meteorological Society
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in
any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written
permission of the publisher.
Published by the American Meteorological Society
45 Beacon Street, Boston, MA 02108
Welcome to AMS Climate Studies!
You are about to explore the complexity and wonder of Earth’s climate system. This Climate
Studies Investigations Manual is designed to introduce you to tools that enable you to explore,
analyze, and interpret the workings of Earth’s climate.
This Investigations Manual is composed of self-contained investigations. These learning
experiences draw from actual climate observations and events to assist students in achieving
their stated objectives. The investigations continually build on previous learning experiences
to help the learner form a comprehensive understanding of the Earth’s climate system – your
environment.
Additionally, one case study of a current or recent climatic situation is delivered via the course
website in real time each week during fall and spring semesters in a schedule aligned with the
Investigation Manual’s table of contents (for Investigations 1A through 12B). These “Current
Climate Studies” appear on the course website by noon, Eastern Time, on Monday for optional
use as determined by the course instructor. Current Climate Studies accumulate each semester
and remain available via a website archive. Studies expanding on Manual Investigations 13A
through 15B are posted to the website at the beginning of each fall semester and are available
throughout the year.
Getting Started:
1. Your course instructor will provide you with the specific requirements of the course in which
you are enrolled.
2. The Climate Studies course website login address is:
http://www.ametsoc.org/amsedu/login.cfm
(an alternate if necessary is: http://amsedu.ametsoc.org/amsedu/login.cfm).
Record this address, add this address to your list of bookmarks or favorites for future retrievals.
3. When the page comes up, type the login ID and password provided by your instructor when prompted
for full access to the contents of the page.
Login ID: _________________________________
Password: _________________________________
4. Explore the course website, noting its organization and the kinds of information provided.
Throughout the year, 7 days a week, 24 hours a day, the climatic products displayed are the
latest available. You will learn to interpret and apply many of these products via the AMS
Climate Studies investigations.
5. Complete Investigation Manual activities and other course requirements, including use of
Current Climate Studies, as directed by your instructor.
6. Keep Current! Keep up with the climate news and your climate studies. The climate
affects all of us, everywhere, watch it in action. Visit the AMS Climate Studies website as
frequently as you can.
AMS Climate Studies
Investigations
1A
1B
2A
2B
3A
3B
4A
4B
5A
5B
6A
6B
MODERN Climate Science
Defines “climate”, introduces Earth’s climate system and investigates the AMS Climate
paradigm
Follow the Energy! EARTH’S DYNAMIC CLIMATE SYSTEM
Presents a simplified model of Earth’s energy system to receive and emit radiation
Climate Science from an Empirical Perspective
Examines traditional sources of climatological data
Climate Variability and Change
Investigates a unique case of one possible climate change cause
Solar Energy and Earth’s Climate System
Contrasts the global distribution of incoming solar energy at various latitudes
ATMOSPHERIC CO2, INFRARED RADIATION, AND CLIMATE CHANGE
Examines the absorption of infrared radiation by carbon dioxide
Water, Heat, and Heat Transfer
Compares the heat storage of water to other common substances
Water and Heat Storage at the Earth’s Surface
Contrasts the heat storage in water and soil locations with its implications for Earth’s
climate system
Global Water Cycle
Investigates remote sensing of Earth’s global water cycle
Water Vapor Flux and Topographical Relief
Examines the effect of Earth’s topography on precipitation patterns
Global Atmospheric Circulation
Compares the general circulation of Earth’s atmosphere from theory to practice
Global Atmospheric Circulation – Rossby Waves
Investigates midlatitude tropospheric motions of Rossby waves
7A
7B
8A
8B
9A
9B
10A
10B
11A
11B
12A
12B
Synoptic-scale ATmospheric Circulation – High and Low
Pressure Systems
Describes synoptic scale weather systems
Synoptic-scale ATmospheric Circulation – Wave Cyclones and
Storm Tracks
Investigates development and movement of synoptic scale weather systems
CLIMATE AND AIR/SEA INTERACTIONS – iNTER-ANNUAL to decadal
CLIMATE VARIABILITY
Considers variability in climate from evolving air-sea interactions
Coastal Upwelling and Coastal Climates
Examines coastal climates that result from oceanic upwelling
PETM: A Possible Analog to Modern Climate Change
Investigates an historic analog climate state to rapid change mechanisms
methane Hydrates: major implications FOR CLIMATE
Demonstrates one climate system component that may trigger rapid system change
Climate and Climate Variability from the Instrumental
Record
Explores climate variability evidenced in the empirical record
Rice Growing and Climate Change
Displays an example of climate variability or change and its possible impact on
agriculture
Volcanism and Climate Variability
Explores one natural forcing mechanism determined from the paleoclimate record
Snow and Ice Albedo Feedback in Earth’s Climate System
Examines an important feedback mechanism in the climate system and its evidence
Climate Change and Radiative Forcing
Compares radiative forcings of the climate system by various natural and human
mechanisms
The Ocean in Earth’s Climate System
Examines evidence of climate change in Earth’s largest energy reservoir – the ocean
13A
13B
14A
14B
15A
15B
Visualizing Climate
Examines traditional displays of empirical climate data and related classification
schemes
Climate Variability and Short-Term Forecasting
Looks at short-term climate predictions based on climate variability
Climate Mitigation and Adaptation Strategies
Examines climate mitigation and adaptation strategies for the future
Geoengineering the Climate
Considers global geoengineering strategies and feasibility
Climate Mitigation through carbon emission Cap-and-Trade
Investigates the Cap-and-Trade Process for mitigation of climate change
Carbon Dioxide Emissions, Carbon Footprints, and Public
policy
Explores the lifetime of atmospheric carbon dioxide and carbon “footprints” as well as
public opinion on climate change
CHAPTER 1
CLIMATE SCIENCE FOR TODAY’S WORLD
Case-in-Point
Driving Question
Defining Climate
Climate versus Weather
The Climatic Norm
Historical Perspective
Climate and Society
The Climate System
Atmosphere
Hydrosphere
Cryosphere
Geosphere
Biosphere
Subsystem Interactions: Biogeochemical Cycles
The Climate Paradigm
Conclusions/Basic Understandings/Enduring Ideas
Review/Critical Thinking
ESSAY: Evolution of Earth’s Climate System
ESSAY: Asteroids, Climate Change, and Mass Extinctions
Dwindling arctic sea-ice. [NASA Earth Observatory]
Case-in-Point
Today’s much discussed proposition that human activity
can contribute to climate change is not new. In fact,
during much of the 18th and 19th centuries, debate raged
among natural scientists over whether deforestation
and cultivation of land in America were responsible for
changing the climate. In 1650, prior to colonization, tall
forests blanketed most of what is now the eastern United
States, but over the subsequent 200 years, settlers cleared
the forests over much of New England, the mid-Atlantic
region, and parts of the Midwest. By about 1920, almost
all of the tall forests were gone as the land was converted
to farms, towns, and cities.
Among the earliest proponents of a possible link
between land clearing and climate change was Benjamin
Franklin (1706-1790), a man of many talents and interests.
In 1763, Franklin wrote that by clearing the woods,
colonists exposed the once shaded soil surface to more
direct sunshine thereby absorbing more heat. Hence, snow
melted more quickly. Thomas Jefferson (1743-1826), third
President of the United States, shared Franklin’s view
that deforestation and cultivation of the soil ameliorated
the climate. Others claimed that these landscape changes
caused winters to be less severe and summers to be
more moderate. However, Franklin and Jefferson also
recognized that many years of instrument-based weather
observations would be needed to firmly establish a link
between deforestation and climate change.
Prior to the end of the 18th century, Noah
Webster (1758-1843), author of the first American
dictionary, weighed in on the climate change debate.
According to Webster, most proponents of a warming
climate based their arguments largely on anecdotal
information and faulty memories of what the weather
had been like many years prior. While rejecting the idea
of a large-scale warming trend, Webster believed that
deforestation and cultivation of land in America had
2
Chapter 1 Climate Science for Today’s World
caused the climate to become seasonally more variable
because cleared land would be hotter in summer and
colder in winter.
Until the early decades of the 19th century, most
information on climate was qualitative, consisting of pronouncements by various authorities or the memories of
the elderly. In the second half of the 19th century with the
increasingly widespread availability of thermometers and
other weather instruments along with establishment of regular weather observational networks operated by the U.S.
Army Medical Department and the Smithsonian Institution, quantitative climate data became available for analysis. Those data failed to show an unequivocal relationship
between deforestation, cultivation, and climate change.
Today, climate scientists remain intrigued by the
possible influence of land use patterns on climate. Vegetation is an important component of the climate system (e.g.,
slowing the wind, transpiring water vapor into the atmosphere, absorbing sunlight and carbon dioxide for photosynthesis). It is reasonable to assume that transformation of
forests to cropland would affect these and other processes
that influence the climate. Unlike their early predecessors in
the climate/land use debate, today’s climate scientists have
access to regional climate models to predict the role played
by changes in land use patterns on climate. These computerized numerical models simulate the interactions between
vegetation and atmosphere taking into account biological
and physical characteristics of the land.
Driving Question:
What is the climate system and why should we be concerned about climate
and climate change?
W
e are about to embark on a systematic study of
climate, climate variability, and climate change.
Earth is a mosaic of many climate types, each featuring a
unique combination of physical, chemical, and biological
characteristics. Differences in climate distinguish, for
example, deserts from rainforests, temperate regions from
glacier-bound polar localities, and treeless tundra from
subtropical savanna. We will come to understand the spatial
and temporal (time) variations in climate as a response
to many interacting forcing agents or mechanisms both
internal and external to the planetary system. At the same
time we will become familiar with the scientific principles
and basic understandings that underlie the operations and
interactions of those forcing agents and mechanisms. This
is climate science, the systematic study of the mean state
of the atmosphere at a specified location and time period
as governed by natural laws.
Our study of climate science provides valuable
insights into one of the most pressing environmental
issues of our time: global climate change. We explore
the many possible causes of climate change with special
emphasis on the role played by human activity (e.g.,
burning fossil fuels, clearing vegetation). A thorough
grounding in climate science enables us to comprehend
the implications of anthropogenic climate change, how
each of us contributes to the problem, and how each of us
can be part of the solution to the problem.
Our primary objective in this opening chapter is
to begin constructing a framework for our study of climate
science. We begin by defining climate and showing how
climate relates to weather, as the state of the atmosphere
plays a dominant role in determining the global and
regional climate. The essential value in studying climate
science stems from the ecological and societal impacts
of climate and climate change. Climate is the ultimate
environmental control that governs our lives; for example,
what crops can be cultivated, the supply of fresh water,
and the average heating and cooling requirements for
homes.
By its very nature, climate science is interdisciplinary, drawing on principles and basic understandings of many scientific disciplines. We recognize climate
as a system in which Earth’s major subsystems (i.e.,
atmosphere, hydrosphere, cryosphere, geosphere, and
biosphere) individually and in concert function as controls of climate. Linking these subsystems are biogeochemical cycles (e.g., global carbon cycle, global water
cycle, global nitrogen cycle), pathways for transfer of
climate-sensitive materials (e.g., greenhouse gases, atmospheric particulates) and energy and energy transfers
among Earth-bound reservoirs. This chapter closes with
the climate paradigm, a rudimentary theoretical framework that encapsulates the basic ingredients of our study
of climate science.
Chapter 1 Climate Science for Today’s World
Defining Climate
The study of climate began with the ancient Greek
philosophers and geographers. Climate is derived from
the Greek word klima meaning “slope,” referring to the
variation in the amount of sunshine received at Earth’s
surface due to the regular changes in the Sun’s angle of
inclination upon a spherical Earth. This was the original
basis for subdividing Earth into different climate zones.
Parmenides, a philosopher and poet who lived in the
mid 5th century BCE, is credited with devising the first
climate classification scheme. His classification consists
of a latitude-bounded five-zone division of Earth’s
surface based on the intensity of sunshine: a torrid
zone, two temperate zones, and two frigid zones (Figure
1.1). According to Parmenides, the torrid zone was
uninhabitable because of heat and the frigid zones were
uninhabitable because of extreme cold.
Hippocrates (ca. BCE 460-370), considered the
founder of medicine, authored the first climatography, On
Airs, Waters, and Places, about BCE 400. (A climatogra­
phy is a graphical, tabular or narrative description of the
climate.) Aristotle who adopted Parmenides’ climate classification, followed in about BCE 350 with Meteorologica,
the first treatise on meteorology, which literally means the
study of anything from the sky. Strabo (ca. BCE 64 – CE
24), author of the 17-volume treatise Geographica, noted
Frigid zone
Temperate zone
Torrid zone
Equator
Torrid zone
Temperate zone
Frigid zone
FIGURE 1.1
Parmenides developed the first global climate classification
scheme in the mid 5th century BCE.
3
that climate zones correspond to temperature differences
as well as amount of sunshine. He was the first to observe
that temperature varied with both latitude and altitude. In
addition, Strabo attributed local variations in climate to
topography and land/water distribution.
CLIMATE VERSUS WEATHER
Weather and climate are closely related concepts.
According to an old saying, climate is what we expect
and weather is what actually happens. In this section, we
describe the relationship between weather and climate
and focus on two complementary working definitions of
climate: an empirical definition that is based on statistics
and a dynamic definition that incorporates the forces that
govern climate. The first describes climate whereas the
second seeks to explain climate.
Everyone has considerable experience with the
weather. After all, each of us has lived with weather our
entire life. Regardless of where we live or what we do, we
are well aware of the far-reaching influence of weather.
To some extent, weather dictates our clothing, the price
of orange juice and coffee in the grocery store, our choice
of recreational activities, and even the outcome of a
football game. Before setting out in the morning, most of
us check the weather forecast on the radio or TV or glance
out the window to scan the sky or read the thermometer.
Every day we gather information on the weather through
our senses, the media, and perhaps our own weather
instruments. And from that experience, we develop some
basic understandings regarding the atmosphere, weather,
and climate.
Weather is defined as the state of the atmosphere
at some place and time, described in terms of such variables
as temperature, humidity, cloudiness, precipitation, and
wind speed and direction. Thousands of weather stations
around the world monitor these weather variables at
Earth’s surface at least hourly every day. A place and time
must be specified when describing the weather because
the atmosphere is dynamic and its state changes from
one place to another and with time. When it is cold and
snowy in Boston, it might be warm and humid in Miami
and hot and dry in Phoenix. From personal experience,
we know that tomorrow’s weather may differ markedly
from today’s weather. If you don’t like the weather, wait a
minute is another old saying that is not far from the truth
in many areas of the nation. Meteorology is the study of
the atmosphere, processes that cause weather, and the life
cycle of weather systems.
While weather often varies from one day to the
next, we are aware that the weather of a particular locality
4
Chapter 1 Climate Science for Today’s World
tends to follow reasonably consistent seasonal variations,
with temperatures higher in summer and lower in winter.
Some parts of the world feature monsoon climates with
distinct rainy and dry seasons. We associate the tropics
with warmer weather and seasonal temperature contrasts
that are less than in polar latitudes. In fact, experienced
meteorologists can identify readily the season from
a cursory glance at the weather pattern (atmospheric
circulation) depicted on a weather map. These are all
aspects of climate.
An easy and popular way of summarizing local
or regional climate is in terms of the averages of weather
elements, such as temperature and precipitation, derived
from observations taken over a span of many years. In this
empirically-based context, climate is defined as weather
(the state of the atmosphere) at some locality averaged
over a specified time interval. Climate must be specified
for a particular place and period because, like weather,
climate varies both spatially and temporally. Thus, for
example, the climate of Chicago differs from that of New
Orleans, and winters in Chicago were somewhat milder in
the 1980s and 1990s than in the 1880s and 1890s.
In addition to average values of weather elements,
the climate record includes extremes in weather. Climatic
summaries typically tabulate extremes such as the coldest,
warmest, driest, wettest, snowiest, or windiest day, month
or year on record for some locality. Extremes are useful
aspects of the climate record if only because what has
happened in the past can happen again. For this reason,
for example, farmers are interested in not only the average
rainfall during the growing season but also the frequency
of exceptionally wet or dry growing seasons. In essence,
records of weather extremes provide a perspective on the
variability of local or regional climate.
In 1935, delegates to the International
Meteorological Conference at Warsaw, Poland,
standardized the averaging period for the climate record.
Previously it was common practice to compute averages for
the entire period of station record even though the period
of record varied from one station to another. This practice
was justified by the erroneous assumption that the climate
was static. By international convention, average values
of weather elements are computed for a 30-year period
beginning with the first year of a decade. (Apparently,
selection of 30 years was based on the Brückner cycle,
popular in the late 19th century and consisting of alternating
episodes of cool-damp and warm-dry weather having a
period of nearly 30 years. However, the Brückner cycle
has been discredited as a product of statistical smoothing
of data.) At the close of the decade, the averaging period
is moved forward 10 years. Current climatic summaries
are based on weather records from 1971 to 2000. Average
July rainfall, for example, is the simple average of the
total rainfall measured during each of thirty consecutive
Julys from 1971 through 2000.
Selection of a 30-year period for averaging
weather data may be inappropriate for some applications
because climate varies over a broad range of time scales
and can change significantly in periods much shorter than
30 years. For example, El Niño refers to an inter-annual
variation in climate involving air/sea interactions in the
tropical Pacific and weather extremes in various parts of
the world (Chapter 8). The phenomenon typically lasts for
12 to 18 months and occurs about every 3 to 7 years. For
some purposes, a 30-year period is a short-sighted view
of climate variability. Compared to the long-term climate
record, for example, the current 1971-2000 averaging
period was unusually mild over much of the nation.
In the United States, 30-year averages are
computed for temperature, precipitation (rain plus melted
snow and ice), and degree days and identified as normals.
Averages of other climate elements such as wind speed
and humidity are derived from the entire period of record
or at least the period when observations were made at
the same location. Other useful climate elements include
average seasonal snowfall, length of growing season,
percent of possible sunshine, and number of days with
dense fog. Tabulation of extreme values of weather
elements is usually also drawn from the entire period of
the observational record.
Climatic summaries (e.g., Local Climatological
Data) are available in tabular formats for major cities (along
with a narrative description of the local or regional climate)
as well as climatic divisions of each state. The National
Oceanic and Atmospheric Administration’s (NOAA’s)
National Weather Service is responsible for gathering
the basic weather data used in generating the nation’s
climatological summaries. Data are processed, archived,
and made available for users by NOAA’s National Climatic
Data Center (NCDC) in Asheville, NC.
While the empirical definition of climate (in
terms of statistical summaries) is informative and useful,
the dynamic definition of climate is more fundamental.
It addresses the nature and controls of Earth’s climate
together with the causes of climate variability and change
operating on all time scales. Climate differs from season
to season and with those variations in climate, the array of
weather patterns that characterize one season differs from
the array of characteristic weather patterns of another
season. (As mentioned earlier, this explains why an
Chapter 1 Climate Science for Today’s World
experienced meteorologist can deduce the season from the
weather pattern.) The status of the planetary system (that
is, the Earth-atmosphere-land-ocean system) determines
(or selects) the array of possible weather patterns for
any season. In essence, this status constitutes boundary
conditions (i.e., forcing agents and mechanisms) such as
incoming solar radiation and the albedo (reflectivity) of
Earth’s surface. Hence, in a dynamic context, climate is
defined by the boundary conditions in the planetary system
coupled with the associated typical weather patterns that
vary with the seasons. For example, the higher Sun’s path
across the local sky and the longer daylight length in
Bismarck, ND during July increase the chance of warm
weather and possible thunderstorms, whereas lower Sun
angles and shorter daylight duration during January would
mean colder weather and possible snow.
Climatology, the subject of this book, is the
study of climate, its controls, and spatial and temporal
variability. Climatology is primarily a field science rather
than a laboratory science. The field is the atmosphere and
Earth’s surface where data are obtained by direct (in situ)
measurement by instruments and remote sensing, mostly
by sensors flown aboard Earth-orbiting satellites (Chapter
2). Nonetheless, laboratory work is important in climatology; it involves analysis of climate-sensitive samples
gathered from the field (Figure 1.2). For example, analysis
of glacial ice cores, tree growth rings, pollen profiles, and
deep-sea sediment cores enables climatologists to reconstruct the climate record prior to the era of weather instruments (Chapter 9).
FIGURE 1.2
The thickness of annual tree growth rings provides information on
past variations in climate, especially the frequency of drought.
5
The only scientific experiments routinely
conducted by climate scientists involve manipulation of
numerical climate models. Usually these global or regional
models are used to predict the climatic consequences of
change in the boundary conditions of Earth’s climate system.
Furthermore, climatology is an interdisciplinary science
that reveals how the various components of the natural
world are interconnected. For example, the composition of
the atmosphere is the end product of many processes where
gases are emitted (e.g., via volcanic eruptions) or absorbed
(e.g., gases dissolving in the ocean). The composition of
the atmosphere, in turn, affects the ocean, living organisms,
geological processes, and climate.
THE CLIMATIC NORM
Traditionally, the climatic norm, or normal, is
equated to the average value of some climatic element such
as temperature or precipitation. This tradition sometimes
fosters misconceptions. For one, “normal” may be taken
to imply that the climate is static when, in fact, climate is
inherently variable with time. Furthermore, “normal” may
imply that climatic elements occur at a frequency given by
a Gaussian (bell-shaped) probability distribution, although
many climatic elements are non-Gaussian.
Many people assume that the mean value of a particular climatic element is the same as the median (middle
value); that is, 50% of all cases are above the mean and
50% of all cases fall below the mean. This assumption is
reasonable for some climatic elements such as temperature, which approximates a simple Gaussian-type probability distribution (Figure 1.3A). Hence, for example,
we might expect about half the Julys will be warmer and
half the Julys will be cooler than the 30-year mean July
temperature. On the other hand, the distribution of some
climatic elements, such as precipitation, is non-Gaussian,
and the mean value is not the same as the median value
(Figure 1.3B). In a dry climate that is subject to infrequent
deluges of rain during the summer, considerably fewer
than half the Julys are wetter than the mean and many
more than half of Julys are drier than the mean. In fact,
for many purposes the median value of precipitation is a
more useful description of climate than the mean value as
extremes (outliers) are given less weight.
For our purposes, we can think of the climatic
norm for some locality as encompassing the total
variation in the climate record, that is, both averages plus
extremes. This implies, for example, that an exceptionally
cold winter actually may not be “abnormal” because its
mean temperature may fall within the expected range of
variability of winter temperature at that location.
6
Chapter 1 Climate Science for Today’s World
A. Distribution of average daily temperature
Des Moines, IA; July 1971-2000 normals
80
250
Statistics:
Standard deviation: 5.78°F
Range: 59° - 91°F
Statistics
Daily average: 0.13 inches
Range: 0.00 - 3.18 inches
200
Relative frequency
Counts (930)
Normal (Gaussian)
distribution
60
Relative frequency
B. Distribution of measurable daily precipitation
Des Moines, IA; July 1971-2000 normals
40
20
Counts (298 out of 930 possible)
150
100
50
0
0
50
60
70
80
90
Temperature bins (°F)
100
0
1
2
3
4
Precipitation bins (in.)
FIGURE 1.3
Distribution of average daily temperature for the month of July in Des Moines, IA, for 1971-2000 (A). Distribution of measurable daily precipitation
for the month of July in Des Moines, IA, for 1971-2000 (B). [Courtesy of E.J. Hopkins]
HISTORICAL PERSPECTIVE
Early observers kept records of weather
conditions using primitive instruments or qualitative
descriptions, jotting them down in journals or diaries. In
North America, the first systematic weather observations
were made in 1644-1645 at Old Swedes Fort (now
Wilmington, DE). The observer was Reverend John
Campanius (1601-1683), chaplain of the Swedish military
expedition. Campanius had no weather instruments,
however. He wrote in his diary qualitative descriptions
of temperature, humidity, wind, and weather. Campanius
returned to Sweden in 1648 but fifty years passed before
his grandson published his weather observations.
Long-term
instrument-based
temperature
records began in Philadelphia in 1731; Charleston, SC,
in 1738; and Cambridge, MA, in 1753. The New Haven,
CT, temperature record began in 1781 and continues
uninterrupted today.
On 2 May 1814, James Tilton, M.D., U.S.
Surgeon General, issued an order that marked the first
step in the eventual establishment of a national network
of weather and climate observing stations. Tilton
directed the Army Medical Corps to begin a diary of
weather conditions at army posts, with responsibility
for observations in the hands of the post’s chief medical
officer. Tilton’s objective was to assess the relationship
between weather and the health of the troops, for it was
widely believed at the time that weather and its seasonal
changes were important factors in the onset of disease.
Even well into the 20th century, more troops lost their
lives to disease than combat. Tilton also wanted to learn
more about the climate of the then sparsely populated
interior of the continent.
The War of 1812 prevented immediate compliance
with Tilton’s order. In 1818, Joseph Lovell, M.D., succeeded
Tilton as Surgeon General and issued formal instructions
for taking weather observations. By 1838, 16 Army posts
had recorded at least 10 complete (although not always
successive) years of weather observations. By the close of
the American Civil War, weather records had been tabulated
for varying periods at 143 Army posts. In 1826, Lovell
began compiling, summarizing, and publishing the data
and for this reason Lovell, rather than Tilton, is sometimes
credited with founding the federal government’s system of
weather and climate observations.
In the mid-1800s, Joseph Henry (17971878), first secretary of the Smithsonian Institution in
Washington, DC, established a national network of
volunteer observers who mailed monthly weather reports
to the Smithsonian. The number of citizen observers
(mostly farmers, educators, or public servants) peaked at
nearly 600 just prior to the American Civil War. Henry
Chapter 1 Climate Science for Today’s World
knew the value of rapid communication of weather
data and realized the potential of the newly invented
electric telegraph in achieving this goal. In 1849, Henry
persuaded the heads of several telegraph companies to
direct their telegraphers in major cities to take weather
observations at the opening of each business day and to
transmit these data free of charge to the Smithsonian.
Henry supplied thermometers and barometers (for
measuring air pressure). Availability of simultaneous
weather observations enabled Henry to prepare the
first national weather map in 1850; later he regularly
displayed the daily weather map for public viewing in
the Great Hall of the Smithsonian building. By 1860, 42
telegraph stations, mostly east of the Mississippi River,
were participating in the Smithsonian network.
The success of Henry’s Smithsonian network
and another telegraphic-based network operated
by Cleveland Abbe (1838-1916) at the Mitchell
Astronomical Observatory in Cincinnati, OH,
persuaded the U.S. Congress to establish a telegraphbased storm warning system for the Great Lakes. In the
1860s, surprise storms sweeping across the Great Lakes
were responsible for a great loss of life and property
from shipwrecks. President Ulysses S. Grant (18221885) signed the Congressional resolution into law on
9 February 1870 and the network, initially composed
of 24 stations, began operating on 1 November 1870
under the authority of the U.S. Army Signal Corps.
Although the network was originally authorized for
the Great Lakes, in 1872, Congress appropriated
funds for expanding the storm-warning network to the
entire nation. The network soon encompassed stations
previously operated by the Army Medical Department,
Smithsonian Institution, U.S. Army Corps of Engineers,
and Cleveland Abbe. With the expansion of telegraph
service nationwide, the number of Signal Corps stations
regularly reporting daily weather observations reached
110 by 1880.
On 1 July 1891, the nation’s weather network
was transferred from military to civilian hands in the
new U.S. Weather Bureau within the U.S. Department of
Agriculture, with a special mandate to provide weather
and climate guidance for farmers. Forty-nine years later,
aviation’s growing need for weather information spurred
the transfer of the Weather Bureau to the Commerce
Department. Many cities saw their Weather Bureau
offices relocated from downtown to an airport, usually
in a rural area well outside the city. In 1965, the Weather
Bureau was reorganized as the National Weather Service
(NWS) within the Environmental Science Services
7
Administration (ESSA), which became the National
Oceanic and Atmospheric Administration (NOAA)
in 1971.
Today, NWS Forecast Offices operate at 122
locations nationwide. NWS and the Federal Aviation
Administration (FAA) operate nearly 840 automated
weather stations, many at airports, which have replaced
the old system of manual hourly observations. This
Automated Surface Observing System (ASOS) consists
of electronic sensors, computers, and fully automated
communications ports (Figure 1.4). Twenty-four hours
a day, ASOS feeds data to NWS Forecast Offices and
airport control towers. Nearly 1100 additional automatic
weather stations, which are funded by other federal and
state agencies, supply hourly weather data from smaller
airports.
FIGURE 1.4
The National Weather Service’s Automated Surface Observing
System (ASOS) consists of electronic meteorological sensors,
computers, and communications ports that record and transmit
atmospheric conditions (e.g., temperature, humidity, precipitation,
wind) automatically 24 hours a day.
8
Chapter 1 Climate Science for Today’s World
FIGURE 1.5
This NWS Cooperative Observer Station is equipped with
maximum and minimum recording thermometers housed in a
louvered wooden instrument shelter. Nearby is a standard rain
gauge. Instruments are read and reset once daily by a volunteer
observer.
In addition to the numerous weather stations
that provide observational data primarily for weather
forecasting and aviation, another 11,700 cooperative
weather stations are scattered across the nation (Figure
1.5). These stations, derived from the old Army Medical
Department and Smithsonian networks, are staffed by
volunteers who monitor instruments provided by the
National Weather Service. The principal mission of member
stations of the NWS Cooperative Observer Network is
to record data for climatic, hydrologic, and agricultural
purposes. Observers report 24-hr precipitation totals and
maximum/minimum temperatures based on observations
made daily at 8 a.m. local time; some observers also
report river levels. Traditionally, observers mailed in
monthly reports or telephoned their reports to the local
NWS Weather Forecast Office; more recently they enter
that data into a computer which formats and transmits data
to computer workstations in the NWS Advanced Weather
Interactive Processing System (AWIPS).
Climate and Society
Probably the single most important reason for studying
climate science is the many linkages between climate and
society. For one, climate imposes constraints on social and
economic development. For example, the abject poverty of
North Africa’s Sahel in large measure is due to the region’s
subtropical climate that is plagued by multi-decadal
droughts (Chapter 5). In other regions, climate provides
resources that are exploited to the advantage of society. For
example, some climates favor winter or summer recreational
activities (e.g., skiing, boating) that attract vacationers and
feed the local economy. Severe weather (e.g., tornadoes,
hurricanes, floods, heat waves, cold waves, and drought)
can cause deaths and injuries, considerable long-term
disruption of communities, property damage, and economic
loss. The impact of Hurricane Katrina on the Gulf Coast is
still being felt many years after that weather system made
landfall (August 2005).
Regardless of a nation’s status as developed or
developing, it is not possible to weather- or climate-proof
society to prevent damage to life and property. In the
agricultural sector, for example, the prevailing strategy is
to depend on technology to circumvent climate constraints.
Where water supply is limited, farmers and ranchers
routinely rely on irrigation water usually pumped from
subsurface aquifers (e.g., the High Plains Aquifer in the
central U.S.) or transferred via aqueducts and canals from
other watersheds. Because of consumers’ food preferences
and for economic reasons, this strategy is preferred to
matching crops to the local or regional climate (e.g., dry
land farming). Other strategies include construction of dams
and reservoirs to control runoff and genetic manipulation
to breed drought resistant crops. Although these strategies
have some success, they have limitations and often require
tradeoffs. For example, many rivers around the world lose
so much of their flow to diversions (mostly for irrigation)
that they are reduced to a trickle or completely dry up prior
to reaching the sea at least during part of the year. Consider,
for example, the Colorado River.
By far, the nation’s most exploited watershed
is that of the Colorado River, the major source of water
for the arid and semi-arid American Southwest. The
Colorado River winds its way some 2240 km (1400
mi)1 from its headwaters in the snow-capped Rocky
Mountains of Colorado to the Gulf of California in
extreme northwest Mexico (Figure 1.6). Along the river’s
course, ten major dams and reservoirs (e.g., Lake Mead
behind Hoover Dam, Lake Powell behind Glen Canyon
Dam) regulate its flow. Water is diverted from the river
to irrigate about 800,000 hectares (2 million acres) and
meet the water needs of 21 million people. Governed
by the Colorado River Compact, aqueducts and canals
divert water for use in 7 states and northern Mexico. A
1
For unit conversions, see Appendix I.
Chapter 1 Climate Science for Today’s World
Salt
Lake
City
Gr e
en
R.
Flaming Gorge
Reservoir
.
oR
rad
Colo
Denver
Lake Powell
Lake Meade
.
oR
rad
Colo
Lake Mohave
Flagstaff
Colorad
o R.
Lake Havasu
Phoenix
Gila
R.
FIGURE 1.6
The nation’s most exploited watershed is that of the Colorado
River, the major source of water for the arid and semi-arid
American Southwest. The Colorado River winds its way from its
headwaters in the snow-capped Rocky Mountains of Colorado to
the Gulf of California in extreme northwest Mexico.
714-km (444-mi) aqueduct system transfers water from
the Colorado River to Los Angeles and the irrigation
systems of California’s Central and Imperial Valleys.
The Central Arizona Project, completed in 1993, diverts
Colorado River water from Lake Havasu (behind Parker
Dam) on the Arizona/California border to the thirsty
cities of Phoenix and Tucson. Where its channel finally
enters the sea, watershed transfers and evaporation have
so depleted the river’s discharge that water flows in the
channel only during exceptionally wet years.
Compounding the constraints of climate on society is the prospect of global climate change. The scientific evidence is now convincing that human activity
is influencing climate on a global scale with significant
consequences for society. As we will see in much greater
detail later in this book, burning of fossil fuels (coal, oil,
natural gas) and clearing of vegetation is responsible for a
steady build-up of atmospheric carbon dioxide (CO2) and
enhancement of Earth’s greenhouse effect. This enhancement is exacerbated by other human activities that are increasing the concentration of methane (CH4) and nitrous
oxide (N2O), also greenhouse gases. The consequence is
global warming and alteration of precipitation patterns.
In addition, certain human activities are making
society and ecosystems more vulnerable to climate
9
change. An ecosystem consists of communities of plants
and animals that interact with one another, together with
the physical conditions and chemical substances in a
specific geographical area. Deserts, tropical rain forests,
and estuaries are examples of natural ecosystems. Most
people live in highly modified terrestrial ecosystems
such as cities, towns, farms, or ranches. For example,
the human population of the coastal zone is rising
rapidly putting more and more people at risk from rising
sea level. The 673 coastal counties of the U.S. represent
17% of the nation’s land area but have three times the
nation’s average population density. The population of
Florida’s coastal counties increased 73% between 1980
and 2003. A consequence of global warming is sea level
rise (due to melting glaciers and thermal expansion
of sea water); higher sea level, in turn, increases the
hazards associated with storm surges (rise in water
level caused by strong onshore winds in tropical and
other coastal storms). These hazards include coastal
flooding, accelerated coastal erosion, and considerable
damage to homes, businesses, and infra-structure (e.g.,
roads, bridges).
With the human population growing rapidly in
many areas of the globe, more people are forced to migrate
into marginal regions, that is, locales that are particularly
vulnerable to excess soil erosion (by wind or water) or
where barely enough rain falls or the growing season is
hardly long enough to support crops and livestock. These
are typically boundaries between ecosystems, known as
ecotones. Ecotones are particularly vulnerable to climate
change in that even a small change in climate can spell
disaster (e.g., crop failure and famine).
An important consideration regarding weather
and climate extremes (hazards) is societal resilience,
that is, the ability of a society to recover from weatheror climate-related or other natural disasters. For example,
if climate change is accompanied by a higher frequency
of intense hurricanes in the Atlantic Basin, there is even
greater urgency for a coordinated preparedness plan that
would minimize the impact of landfalling hurricanes
especially on low-lying communities along the Gulf
Coast. These preparations must involve investment in
appropriately designed infra-structure that will reduce
flooding and allow for the quick evacuation of populations
that find themselves in harm’s way.
Assessment of societal resilience to climaterelated hazards requires understanding of the regional bias
of severe weather events. The climate record indicates
that although tornadoes have been reported in all states,
they are most frequent in the Midwest (tornado alley).
10
Chapter 1 Climate Science for Today’s World
Hurricanes are most likely to make landfall along the Gulf
and Atlantic Coasts, but are rare along the Pacific Coast.
Droughts are most common on the High Plains whereas
forest fires are most frequent in the West.
Our understanding of the potential impact of
climate and climate change on society requires knowledge
of (1) the structure and function of Earth’s climate system,
(2) interactions of the various components of that system,
and (3) how human activities influence and are influenced
by these systems. We begin in the next section with an
overview of Earth’s climate system.
The Climate System
What is the climate system and, more fundamentally, what
is a system? A system is an entity whose components
interact in an orderly manner according to the laws of
physics, chemistry, and biology. A familiar example of
a system is the human body, which consists of various
identifiable subsystems including the nervous, respiratory,
and reproductive systems, plus the input/output of energy
and matter. In a healthy person, these subsystems function
inter­nally and interact with one another in regular and
predict­able ways that can be studied based upon analysis
of the energy and mass budgets for the systems. Extensive
observations and knowledge of a system enable scientists
to predict how the sys­tem and its components are likely
to respond to changing internal and external conditions.
The ability to predict the future state(s) of a system is
important, for example, in dealing with the complexities
of global climate change and its potential impacts on
Earth’s subsystems and society.
The 1992 United Nations Framework
Convention on Climate Change defines Earth’s climate
system as the totality of the atmosphere, hydrosphere
(including the cryosphere), biosphere and geosphere
and their interactions. In this section, we examine each
subsystem, its composition, basic properties, and some of its
interactions with other components of the climate system.
The view of Planet Earth in Figure 1.7, resembling a “blue
marble,” shows all the major subsystems of the climate
system. The ocean, the most prominent feature covering
more than two-thirds of Earth’s surface, appears blue.
Clouds obscure most of the ice sheets (the major part of the
cryosphere) that cover much of Greenland and Antarctica.
The atmosphere is made visible by swirling storm clouds
over the Pacific Ocean near Mexico and the middle of the
Atlantic Ocean. Viewed edgewise, the atmosphere ap­pears
as a thin, bluish layer. Land (part of the geosphere) is mostly
green because of vegetative cover (biosphere).
FIGURE 1.7
Planet Earth, viewed from space by satellite, appears as a “blue
marble” with its surface mostly ocean water and partially obscured
by swirling masses of clouds. [Courtesy of NASA, Goddard Space
Flight Center]
ATMOSPHERE
Earth’s atmosphere is a relatively thin envelope
of gases and tiny suspended particles surrounding the
planet. Compared to Earth’s diameter, the atmosphere is
like the thin skin of an apple. But the thin atmospheric skin
is essential for life and the orderly functioning of physical,
chemical and biological processes on Earth. While a
person can survive for days without water or food, a lack
of atmospheric oxygen can be fatal within minutes. Air
density decreases with increasing altitude above Earth’s
surface so that about half of the atmosphere’s mass is
concen­trated within about 5.5 km (3.4 mi) of sea level and
99% of its mass occurs below an altitude of 32 km (20
mi). At altitudes approaching 1000 km (620 mi), Earth’s
atmosphere merges with the highly rarefied interplanetary
gases, hydrogen (H2) and helium (He).
Based on the vertical temperature profile, the
atmosphere is divided into four layers (Figure 1.8). The
troposphere (averaging about 10 km or 6 mi thick) is
where the atmosphere interfaces with the hydrosphere,
cryosphere, geosphere, and biosphere and where most
weather takes place. In the troposphere, the average air
temperature drops with increas­ing altitude so that it is
usually colder on mountaintops than in lowlands (Figure
1.9). The troposphere contains 75% of the atmosphere’s
mass and 99% of its water. The stratosphere (10 to 50
km or 6 to 30 mi above Earth’s surface) contains the ozone
Chapter 1 Climate Science for Today’s World
11
shield, which prevents organisms
from exposure to potentially lethal
700
levels of solar ultraviolet (UV)
107
600
radiation. Above the stratosphere is
10-8
the mesosphere where the average
500
108
tempera­ture generally decreases
Thermosphere
400
with altitude; above that is the
-7
10
300
109
thermosphere where the average
10-6
temperature increases with altitude
200
10-5
1010
but is particularly sensitive to
1013
10-4
100
variations in the high energy portion
10-3
of incoming solar radiation.
Mesopause
90
1014
Nitrogen (N2) and oxygen
10-2
80
(O2), the chief atmo­spheric gases,
1015
70
Mesosphere
are
mixed in uniform proportions
10-1
up
to
an altitude of about 80 km (50
60
1016
mi). Not counting water vapor (with
Stratopause
50
1
its highly variable concentration),
1017
nitrogen occu­pies 78.08% by
40
volume of the lower atmosphere,
Stratosphere
10
30
18
and oxygen is 20.95% by volume.
10
20
The next most abundant gases are
100
194
Tropopause
argon (0.93%) and carbon dioxide
19
10
10
500
Troposphere
(0.038%). Many other gases
1000
occur in the atmosphere in trace
-100 -80 -60 -40 -20 0 +20
Temperature (°C)
concentrations, in­cluding ozone
(O3) and methane (CH4) (Table
FIGURE 1.8
1.1). Unlike nitrogen and oxygen,
Based on variations in average air temperature (°C) with altitude (scale on the left), the atmosphere
the percent volume of some of
is divided into the troposphere, stratosphere, mesosphere, and thermosphere. Scales on the right
show the vertical variation of atmospheric pressure in millibars (mb) (the traditional meteorological
these trace gases varies with time
unit of barometric pressure) and the number density of molecules (number of molecules per cm3).
and location.
[Source: US Standard Atmosphere, 1976, NASA, and U.S. Air Force]
In addition to gases, minute
solid and liquid par­ticles, collectively called aerosols,
are suspended in the atmosphere. A flashlight beam in a
darkened room reveals an abundance of tiny dust particles
floating in the air. Indi­vidually, most atmospheric aerosols
are too small to be visible, but in aggregates, such as the
multitude of water droplets and ice crystals composing
clouds, they may be visible. Most aerosols occur in the
lower atmosphere, near their sources on Earth’s surface;
they derive from wind erosion of soil, ocean spray,
forest fires, volcanic eruptions, industrial chimneys, and
the exhaust of motor vehicles. Although the concen­
tration of aerosols in the atmosphere is relatively small,
they participate in some important processes. Aerosols
function as nuclei that promote the formation of clouds
essential for the global water cycle. Some aerosols (e.g.,
FIGURE 1.9
volcanic dust, sulfurous particles) affect the climate
Within the troposphere, the average air temperature decreases
with increasing altitude so that it is generally colder on mountain
by interacting with incoming solar radiation and dust
peaks than in lowlands. Snow persists on peaks even through
blown out over the tropical Atlantic Ocean from North
summer.
Molecules per cm3
Pressure (mb)
Altitude (km)
800
12
Chapter 1 Climate Science for Today’s World
than it emits), but the atmosphere undergoes net
TABLE 1.1
radiational cooling (to
Gases Composing Dry Air in the Lower Atmosphere (below 80 km)
space). Also, net radiational heating occurs in
the tropics, while net raGas
% by Volume
Parts per Million
diational cooling charac­
terizes higher latitudes.
Variations in heating and
Nitrogen (N2)
78.08
780,840.0
cooling rates give rise to
Oxygen (O2)
20.95
209,460.0
temperature gradients,
Argon (Ar)
0.93
9,340.0
which are differences in
Carbon dioxide (CO2)
0.0388
388.0
temperature from one
Neon (Ne)
0.0018
18.0
location to another. In
Helium (He)
0.00052
5.2
response to tem­perature
Methane (CH4)
0.00014
1.4
gradients, the atmoKrypton (Kr)
0.00010
1.0
sphere (and ocean) cirNitrous oxide (N2O)
0.00005
0.5
culates and redistributes
Hydrogen (H)
0.00005
0.5
heat within the climate
Xenon (Xe)
0.000009
0.09
system. Heat is conveyed
Ozone (O3)
0.000007
0.07
from warmer locations
to colder locations, from
Earth’s surface to the atmosphere and from the trop­ics
Africa may affect the development of tropical cyclones
to higher latitudes. As discussed in Chapter 4, the global
(hurricanes and tropical storms).
water cycle and accompanying phase changes of water
The significance of an atmospheric gas is not
play an important role in this planetary-scale transport
nec­essarily related to its concentration. Some atmospheric
of heat energy.
components that are essential for life occur in very low
concentrations. For example, most water vapor is confined
HYDROSPHERE
to the lowest kilometer or so of the atmosphere and is
The hydrosphere is the water component of
never more than about 4% by volume even in the most
the climate system. Water is unique among the chemical
humid places on Earth (e.g., over tropical rainforests and
components of the climate system in that it is the only
seas). But without water vapor, the planet would have no
naturally occurring substance that co-exists in all three
water cycle, no rain or snow, no ocean, and no fresh water.
phases (solid, liquid, and vapor) at the normal range of
Also, without water vapor, Earth would be much too cold
temperature and pressure observed near Earth’s surface.
for most forms of life to exist.
Water continually cycles among reservoirs within the
Although comprising only 0.038% of the
climate system. (We discuss the global water cycle in
lower atmosphere, carbon dioxide is essential for pho­
more detail in Chapter 5.) The ocean, by far the largtosynthesis. Without carbon dioxide, green plants and
est reservoir of water in the hydrosphere, covers about
the food webs they support could not exist. While the
70.8% of the planet’s surface and has an average depth
atmospheric concentration of ozone (O3) is minute, the
of about 3.8 km (2.4 mi). About 96.4% of the hydro­
chemical reactions responsible for its formation (from
sphere is ocean salt water; other saline bodies of water
oxygen) and dissociation (to oxygen) in the stratosphere
account for 0.6%. The next largest reservoir in the hy(mostly at altitudes between 30 and 50 km) shield organ­
drosphere is glacial ice, most of which covers much of
isms on Earth’s surface from potentially lethal levels of
Antarctica and Greenland. Ice and snow make up 2.1%
solar UV radiation.
of water in the hydrosphere. Considerably smaller quanThe atmosphere is dynamic; the atmosphere
tities of water occur on the land surface (lakes, rivers),
continually circulates in response to different rates of
in the subsurface (soil moisture, groundwater), the atheating and cooling within the rotating planetary system.
mosphere (water vapor, clouds, precipitation), and bioOn an aver­age annual basis, Earth’s surface experiences
sphere (plants, animals).
net radiational heating (absorbing more incident radiation
Chapter 1 Climate Science for Today’s World
13
water near Greenland and Iceland and in the Norwegian
and Labrador Seas further increases its density so that
surface waters sink and form a bottom current that flows
southward under equatorial surface waters and into the
South Atlantic as far south as Antarctica. Here, deep
water from the North Atlantic mixes with deep water
around Antarctica. Branches of that cold bottom current
then spread northward into the Atlantic, Indian, and
Pacific basins. Eventually, the water slowly diffuses to the
surface, mainly in the Pacific, and then begins its journey
on the surface through the islands of Indonesia, across the
Indian Ocean, around South Africa, and into the tropical
Atlantic. There, intense heating and evaporation make the
water hot and salty. This surface water is then transported
northward in the Gulf Stream thereby completing the
cycle. This meridional overturning circulation (MOC)
and its transport of heat energy and salt is an important
control of climate.
The hydrosphere is dynamic; water moves
continually through dif­ferent parts of Earth’s landatmosphere-ocean system and the ocean is the ultimate
destination of all moving water. Water flowing in river or
stream channels may take a few weeks to reach the ocean.
Groundwater typically moves at a very slow pace through
sediment, and the fractures and tiny openings in bedrock,
and feeds into rivers, lakes, or directly into the ocean. The
water of large, deep lakes moves
even more slowly, in some cases
taking centuries to reach the
TABLE 1.2
a
ocean via groundwater flow.
Comparison of Composition of Ocean Water with River Water
The ocean and atmosphere are coupled such
that the wind drives surface ocean currents. Wind-driven
currents are restricted to a surface ocean layer typically
about 100 m (300 ft) deep and take a few months to years
to cross an ocean basin. Ocean currents at much greater
depths are more sluggish and more challenging to study
than surface currents because of greater difficulty in
taking measurements. Movements of deep-ocean waters
are caused primarily by small differences in water density
(mass per unit volume) arising from small differences in
water tem­perature and salinity (a measure of dissolved
salt content). Cold sea water, being denser than warm
water, tends to sink whereas warm water, being less
dense, is buoyed upward by (or floats on) colder water.
Likewise, saltier water is denser than less salty water and
tends to sink, whereas less salty water is buoyed upward.
The combination of temperature and salinity determines
whether a water mass re­mains at its original depth or
sinks to the ocean bottom. Even though deep currents are
relatively slow, they keep ocean waters well mixed so
that the ocean has a nearly uniform chemical composition
(Table 1.2).
The densest ocean waters form in polar or
nearby subpolar regions. Salty waters become even saltier
where sea ice forms at high latitudes because growing
ice crystals exclude dissolved salts. Chilling of this salty
Chemical Constituent
Silica (SiO2)
Iron (Fe)
Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Bicarbonate (HCO3)
Sulfate (SO4)
Chloride (Cl)
Nitrate (NO3)
Bromide (Br)
Total
Source: U.S. Geological Survey
a
Percentage of Total Salt Content
Ocean Water
River Water
-
-
1.19
3.72
30.53
1.11
0.42
7.67
55.16
-
0.20
14.51
0.74
16.62
4.54
6.98
2.55
31.90
12.41
8.64
1.11
-
100.00
100.00
CRYOSPHERE
The frozen portion
of the hydrosphere, known as
the cryosphere, encompasses
massive continental (glacial) ice
sheets, much smaller ice caps
and mountain glaciers, ice in
permanently frozen ground (per­
mafrost), and the pack ice and
ice bergs floating at sea. All of
these ice types except pack ice
(frozen sea water) and undersea
permafrost are fresh ­water. A
glacier is a mass of ice that flows
internally under the influence
of gravity (Figure 1.10). The
Greenland and Antarctic ice
sheets in places are up to 3 km
(1.8 mi) thick. The Antarctic
14
Chapter 1 Climate Science for Today’s World
and atmospheric composition
extending as far back as hundreds of thousands of years—
to 800,000 years or more in
Antarctica (Chapter 9).
Under the influence
of gravity, glacial ice flows
slowly from sources at higher
latitudes and higher elevations
(where some winter snow
survives the summer) to lower
latitudes and lower elevations,
where the ice either melts or
flows into the nearby ocean.
Around Antarctica, streams
of glacial ice flow out to the
ocean. Ice, being less dense
than seawater, floats, forming
ice shelves (typically about
500 m or 1600 ft thick). Thick
masses of ice eventually break
off the shelf edge, forming
flat-topped icebergs that are
carried by surface ocean
currents around Antarctica
FIGURE 1.10
(Figure 1.11). Likewise,
Glaciers form in high mountain valleys where the annual snowfall is greater than annual snowmelt.
irregularly shaped icebergs
break off the glacial ice
streams of Greenland and flow out into the North Atlantic
ice sheet contains 90% of all ice on Earth. Much smaller
Ocean, posing a hazard to navigation. In 1912, the newly
glaciers (tens to hun­dreds of meters thick) primarily
launched luxury liner, RMS Titanic, struck a Greenland
occupy the highest moun­tain valleys on all continents. At
iceberg south­east of Newfoundland and sank with the
present, glacial ice covers about 10% of the planet’s land
loss of more than 1500 lives.
area but at times during the past 1.7 million years, glacial
Most sea ice surrounding Antarctica forms each
ice expanded over as much as 30% of the land surface,
winter through freezing of surface seawater. During sum­
primarily in the Northern Hemi­sphere. At the peak of the
mer most of the sea ice around Antarctica melts, whereas
last glacial advance, about 20,000 to 18,000 years ago, the
in the Arctic Ocean sea ice can persist for several years
Laurentide ice sheet covered much of the area that is now
before flowing out through Fram Strait into the Greenland
Canada and the northern states of the United States. At
Sea, and eventually melting. This “multi-year” ice loses
the same time, a smaller ice sheet buried the British Isles
salt content with age as brine, trapped between ice crystals,
and portions of northwest Europe. Meanwhile, mountain
melts downward, so that Eskimos can harvest this older,
glaciers worldwide thickened and expanded.
less salty ice for drinking water.
Glaciers form where annual snowfall exceeds
How long is water frozen into glaciers? Glaciers
an­nual snowmelt. As snow accumulates, the pressure exnormally grow (thicken and advance) and shrink (thin
erted by the new snow converts underlying snow to ice. As
and retreat) slowly in response to changes in climate.
the ice forms, it preserves traces of the original seasonal
Mountain glaciers respond to climate change on time
layering of snow and traps air bubbles. Chemical analyscales of a decade. Until recently, scientists had assumed
sis of the ice layers and air bubbles in the ice provides
that the response time for the Greenland and Antarctic
clues to climatic conditions at the time the original snow
ice sheets is measured in millennia; however, in 2007
fell. Ice cores extracted from the Greenland and Antarctic
scientists reported that two outlet glaciers that drain the
ice sheets yield information on changes in Earth’s climate
Chapter 1 Climate Science for Today’s World
15
FIGURE 1.11
A massive iceberg (42 km by 17 km or 26 mi by 10.5 mi) is shown breaking off Pine Island Glacier, West Antarctica (75 degrees S, 102 degrees
W) in early November 2001 along a large fracture that formed across the glacier in mid 2000. Images of the glacier were obtained by the Multiangle Imaging SpectroRadiometer (MISR) instrument onboard NASA’s Terra spacecraft. Pine Island Glacier is the largest discharger of ice in
Antarctica and the continent’s fastest moving glacier. [Courtesy of NASA]
Greenland ice sheet exhibited significant changes in
discharge in only a few years. This finding was confirmed
by changes in ice surface elevation detected by sensors
onboard NASA’s Ice, Cloud, and Land Elevation Satellite
(ICESat). This unexpectedly rapid discharge is likely due
to the flow of large ice streams over subglacial lakes.
Hence, outlet glaciers behave more like mountain glaciers,
raising questions regarding the long-term stability of polar
ice sheets and their response to global climate change
(Chapter 12).
GEOSPHERE
The geosphere is the solid portion of the planet
consisting of rocks, minerals, soil, and sediments. Most of
Earth’s interior cannot be observed directly, the deepest
mines and oil wells do not penetrate the solid Earth more
than a few kilometers. Most of what is known about the
composition and physical properties of Earth’s interior
comes from analysis of seismic waves generated by earth­
quakes and explosions. In addition, meteorites provide
valuable clues regarding the chemical composition of
Earth’s interior. From study of the behavior of seismic
waves that penetrate the planet, geologists have determined
that Earth’s interior consists of four spherical shells: crust,
mantle, and outer and inner cores (Figure 1.12). Earth’s
interior is mostly solid and accounts for much of the mass
of the planet. Earth’s outermost solid skin, called the crust,
ranges in thickness from only 8 km (5 mi) under the ocean
to 70 km (45 mi) in some mountain belts. We live on the
crust and it is the source of almost all rock, mineral, and
fossil fuel (e.g., coal, oil, and natural gas) resources that
are essential for industrial-based economies. The rigid
uppermost portion of the mantle, plus the overlying crust,
constitutes Earth’s lithosphere, averaging 100 km (62
mi) thick. Both surface geological processes and internal
geological processes continually modify the lithosphere.
Surface geological processes encompass weath­
ering and erosion occurring at the interface between the
lithosphere (mainly the crust) and the other Earth sub­
systems. Weathering entails the physical disintegration,
chemical decomposition, or solution of exposed rock. Rock
fragments produced by weathering are known as sediments.
Water plays an important role in weathering by dissolving
soluble rock and minerals, and participating in chemical
re­actions that decompose rock. Water’s unusual physi­cal
property of expanding while freezing can produce sufficient
pressure to fragment rock when the water saturates tiny
cracks and pore spaces. More likely, however, the water is
not as confined and fragmentation is due to stress caused by
the growth of ice lenses within the rock.
16
Chapter 1 Climate Science for Today’s World
Ocean
Crust
Lithosphere
Mantle
Crust
Mantle
Outer core
Inner core
FIGURE 1.12
Earth’s interior is divided into the crust, mantle, outer core, and
inner core. The lithosphere is the rigid upper portion of the mantle
plus the overlying crust. (Drawing is not to scale.)
The ultimate weathering product is soil, a mixture
of organic (humus) and inorganic matter (sediment)
on Earth’s surface that supports plants, also sup­plying
nutrients and water. Soils derive from the weathering of
bedrock or sediment, and vary widely in texture (particle
size). A typical soil is 50% open space (pores), roughly
equal proportions of air and water. Plants also participate
in weathering via the physical action of their growing
roots and the carbon dioxide they release to the soil.
Erosion refers to the removal and transport of
sediments by gravity, moving water, glaciers, and wind.
Running water and glaciers are pathways in the global wa­
ter cycle. Erosive agents transport sediments from source
regions (usually highlands) to low-lying depositional areas
(e.g., ocean, lakes). Weathering aids erosion by reducing
massive rock to particles that are sufficiently small to be
transported by agents of erosion. Erosion aids weathering
by removing sediment and exposing fresh surfaces of rock
to the atmosphere and weathering processes. Together,
weathering and erosion work to reduce the el­evation of
the land. Internal geological processes counter surface
geological processes by uplifting land through tectonic
activity, including volcanism and mountain building.
Most tectonic activity occurs at the boundaries between
lithos­pheric plates. The lithosphere is broken into a dozen
massive plates (and many smaller ones) that are slowly
driven (typi­cally less than 20 cm per year) across the
face of the globe by huge convection currents in Earth’s
mantle. Continents are carried on the moving plates and
ocean basins are formed by seafloor spreading.
Plate tectonics probably has operated on the
planet for at least 3 billion years, with continents periodi­
cally assembling into supercontinents and then splitting
apart. The most recent superconti­nent, called Pangaea
(Greek for “all land”), broke apart about 200 million years
ago and its constituent landmasses, the continents of today,
slowly moved to their present loca­tions. Plate tectonics
explains such seemingly anomalous dis­coveries as glacial
sediments in the Sahara and fos­sil coral reefs, indicative
of tropical climates, in northern Wisconsin (Figure 1.13).
Such discoveries reflect climatic conditions hundreds of
millions of years ago when the continents were at different
latitudes than they are today.
Geological processes occurring at boundaries
be­tween plates produce large-scale landscape and ocean
bot­tom features, including mountain ranges, volcanoes,
deep-sea trenches, as well as the ocean basins themselves.
FIGURE 1.13
This exposure of bedrock in northeastern Wisconsin contains
fossil coral that dates from nearly 400 million years ago. Based
on the environmental requirements of modern coral, geoscientists
conclude that 400 million years ago, Wisconsin’s climate was
tropical marine, a drastic difference from today’s warm-summer,
cold-winter climate. Plate tectonics can explain this difference
between ancient and modern environmental conditions.
Chapter 1 Climate Science for Today’s World
Enormous stresses develop at plate boundaries, bending
and fractur­ing bedrock over broad areas. Hot molten rock
material, known as magma, wells up from deep in the
crust or upper mantle and migrates along rock fractures.
Some magma pushes into the upper portion of the crust
where it cools and solidifies into massive bodies of rock,
forming the core of mountain ranges (e.g., Sierra Nevada).
Some magma feeds volcanoes or flows through fractures
in the crust and spreads over Earth’s surface as lava
flows (flood basalts) that cool and slowly solidify (e.g.,
Columbia River Plateau in the Pacific Northwest and the
massive Siberian Traps). At spreading plate boundaries on
the sea floor, upward flowing magma solidifies into new
oceanic crust. Plate tectonics and associated volcanism
are important in geochemical cycling, releasing to the
atmosphere water vapor, carbon dioxide, and other gases
that impact climate.
Volcanic activity is not confined to plate bound­
aries. Some volcanic activity occurs at great distances from
plate boundaries and is due to hot spots in the mantle. A
hot spot is a long-lived source of magma caused by rising
plumes of hot material originating in the mantle (mantle
plumes). Where a plate is situated over a hot spot, magma
may break through the crust and form a volcano. The Big
Island of Hawaii is volcanically active because it sits over
a hot spot located within the mantle under the Pacific
plate. A hot spot underlying Yellowstone National Park
17
is the source of heat for geyser eruptions (including Old
Faithful). Further complicating matters, however, both hot
spots and the overlying lithospheric plate are in motion.
Sometimes hot spots and spreading centers coincide, such
as in Iceland.
BIOSPHERE
All living plants and animals on Earth are
components of the biosphere (Figure 1.14). They range in
size from microscopic single-celled bacteria to the largest
organisms (e.g., redwood trees and blue whales). Bacteria
and other single-celled organisms domi­nate the biosphere,
both on land and in the ocean. The typical animal in the
ocean is the size of a mosquito. Large, multi-cellular
organisms (including humans) are relatively rare on Earth.
Organisms on land or in the atmosphere live close to
Earth’s surface. However, marine organisms occur through­
out the ocean depths and even inhabit rock fractures, vol­
canic vents, and the ocean floor. Certain organisms live
in extreme environments at temperatures and pressures
once considered impossible to support life. In fact, some
scientists estimate that the mass of organisms living in frac­
tured rocks on and below the ocean floor may vastly exceed
the mass of organisms living on or above it.
Photosynthesis and cellular respiration are essen­
tial for life near the surface of the Earth, and exemplify
how the biosphere interacts with the other subsystems of
FIGURE 1.14
Earth’s biosphere viewed by instruments flown onboard NASA’s SeaWiFS (Sea-viewing Wide Field-of-view Sensor) on the SeaStar satellite
launched in August 1997. Biological production is color-coded and highest where it is dark green and lowest where it is violet. White indicates
snow and ice cover. [Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE]
18
Chapter 1 Climate Science for Today’s World
a food chain, each stage is called a trophic level (or feedthe climate system. Photosyn­thesis is the process whereby
ing level). At most, only 10% of the en­ergy available at
green plants convert light en­ergy from the Sun, carbon
one trophic level is transferred to the next. Biomass, the
dioxide from the atmosphere, and water to sugars and oxygen
total weight or mass of organisms, is more readily mea(O2). The sugars, which contain a relatively large amount
sured than energy, so that scientists describe the transfer
of energy and oxygen, are essential for cellular respiration.
of energy in food chains in terms of so many grams or
Through cellular respira­tion, an organism processes food
kilograms of biomass. Thus 100 g of plants are required
and liberates energy for maintenance, growth, and repro­
to produce 10 g of deer, which in turn produces 1 g of
duction, also releasing carbon dioxide, water, and heat
wolf. Terrestrial and marine food chains are often more
energy to the environment. With few exceptions, sunlight is
complex than our plants-deer-wolves example. With some
the originating source of energy for most or­ganisms living
notable exceptions, marine and terrestrial organisms eat
on land and in the ocean’s surface waters.
many different kinds of food, and in turn, are eaten by
Dependency between organisms on one another
a host of other consumers. These more realistic feeding
(e.g., as a source of food) and on their physical and chemirelationships constitute a food web.
cal environment (e.g., for water, oxygen, carbon dioxide,
Climate is the principal ecological control,
and habitat) is embodied in the concept of ecosystem. Relargely governing the location and species composition
call from earlier in this chapter that ecosystems consist of
of natural ecosystems such as deserts, rain forests, and
plants and animals that interact with one another, together
tundra. For example, the late climatologist Reid A.
with the physical conditions and chemical substances in
Bryson (1920-2008) demonstrated a close relationship
a specific geographical area. An ecosystem is home to
between the region dominated by cold, dry arctic air and
producers (plants), consumers (animals), and decomposthe location of Canada’s coniferous boreal forest (Figure
ers (bacteria, fungi). Producers (also called autotrophs
1.15). Bryson found that the southern boundary of the
for “self-nourishing”) form the base of most ecosystems,
providing
energy-rich
70°
70°
60°
carbohydrates. Consumers that depend directly
or indirectly on plants for
their food are called het­
erotrophs; those that feed
directly on plants are called
60°
herbivores, and those that
50°
prey on other animals are
called carnivores. Animals
that consume both plants
and animals are omnivores.
After death, the remains of
organisms are broken down 50°
by decomposers, usually
bacteria and fungi, which
40°
cycle nutrients back to the
environment, for the plants
to use.
Feeding relation- 40°
ships among organisms,
Boreal forest northern border
Arctic frontal zone, summer position
called a food chain, can be
Boreal forest southern border
Arctic frontal zone, winter position
quite simple. For example,
in a land-based (terrestrial)
food chain, deer (herbi- FIGURE 1.15
vores) eat plants (primary The northern border of Canada’s coniferous boreal forest closely corresponds to the mean location of the
producers), and the wolves leading edge of arctic air in summer. The southern boundary of the boreal forest nearly coincides with the
mean location of arctic air in winter. The leading edge of arctic air is referred to as the arctic front. [Modified
(carnivores) eat the deer. In after R.A. Bryson, 1966. “Air Masses, Streamlines, and the Boreal Forest,” Geographical Bulletin 8(3):266.]
Chapter 1 Climate Science for Today’s World
boreal forest nearly coincides with the average winter
position of the southern edge of the arctic air mass (the
arctic front) while the boreal forest’s northern border
closely corresponds to the average summer position of
the arctic front.
Assuming that the relationship between arctic
air frequency and the boreal forest is more cause/effect
than coincidence, how might a large-scale climate change
affect the forest? A warmer climate would likely mean
fewer days of arctic air and a northward shift of the boreal
forest. What actually happens to the forest, however,
could hinge on the rate of climate change. Relatively rapid
warming may not only shift the ecosystem northward
but also alter the ecosystem’s species composition and
disturb the orderly internal operation of the ecosystem.
For example, rapid climate change could disrupt longestablished predator/prey relationships with implications
for the stability of populations of plants and animals.
Similar observations of close relationships
between vegetation and climate variables on a global basis
were made by the noted German climatologist Wladimir
Köppen (1846-1940) in the early 20th century. This is a
central aspect of his widely used climate classification
system (Chapter 13). We have more to say on this topic
in Chapter 12 along with the potential impact of climate
change on the highly simplified agricultural ecosystems.
Subsystem Interactions:
Biogeochemical Cycles
Biogeochemical cycles are the pathways along which
solids, liquids, and gases move among the various
reservoirs on Earth, often involving physical or chemical
changes to these substances. Accompanying these flows
of materials are transfers and transformations of energy.
Reservoirs in these cycles are found within the subsystems
of the overall planetary system (atmosphere, hydrosphere,
cryosphere, geosphere, and biosphere). Examples of
biogeochemical cycles are the water cycle, car­bon cycle,
oxygen cycle, and nitrogen cycle.
Earth is an open (or flow-through) system for
energy, where energy is defined as the capacity for doing
work. Earth receives energy from the Sun primarily and
some from its own interior while emitting energy in the
form of invisible infrared radiation to space. Along the
way, energy is neither created nor destroyed, although it
is converted from one form to another. This is the law
of energy conservation (also known as the first law of
thermodynamics).
19
The Earth system is essentially closed for matter;
that is, it neither gains nor loses matter over time (except
for meteorites and asteroids). All biogeochemical cycles
obey the law of conservation of matter, which states
that matter can be neither created nor destroyed, but can
change in chemical or physical form. When a log burns
in a fireplace, a portion of the log is converted to ash
and heat energy, while the rest goes up the chimney as
carbon dioxide, water vapor, creosote and heat. In terms
of accountability, all losses from one reservoir in a cycle
can be accounted for as gains in other reservoirs of the
cycle. Stated succinctly, for any reservoir:
Input = Output + Storage
The quantity of a substance stored in a reservoir
depends on the rates at which the material is cycled into
and out of the reservoir. Cycling rate is defined as the
amount of material transferred from one reservoir to
another within a specified period of time. If the input rate
exceeds the output rate, the amount of material stored in
the reservoir increases. If the input rate is less than the
output rate, the amount stored decreases. Over the long
term, the cycling rates of materials among the various
global reservoirs are relatively stable; that is, equilibrium
tends to prevail between the rates of input and output.
Closely related to cycling rate is residence time.
Residence time is the average length of time for a sub­
stance in a reservoir to be replaced completely, that is,
Residence time =
(amount in reservoir)
(rate of addition or removal)
For example, the residence time of a water molecule in
the various reser­voirs of Earth’s land-atmosphere-ocean
system varies from only 10 days in the atmosphere to tens of
thousands of years, or longer, in glacial ice sheets. Residence
time of dissolved constituents of seawater ranges from 100
years for alumi­num (Al) to 260 million years for sodium
(Na). Consider the global cycling of carbon as an illus­tration
of a biogeochemical cycle that has important implications
for climate (Figure 1.16). Through photosynthesis, carbon
dioxide cycles from the atmosphere to green plants where
carbon is incorporated into sugar (C6 H12O6). Plants use
sugar to manufacture other organic compounds includ­ing
fats, proteins, and other carbohydrates. As a byproduct of
cellular respiration, plants and animals transform a por­tion
of the carbon in these organic compounds into CO2 that is
released to the atmosphere. In the ocean, CO2 is cycled into
and out of marine organisms through photosynthesis and
20
Chapter 1 Climate Science for Today’s World
Atmospheric
carbon dioxide
Respiration
Photosynthesis
Combustion
Respiration
Respiration
Decomposers
Combustion
Plant and animal wastes
Bicarbonate
Carbon dioxide
Gradual
production
of fossil fuels
Respiration
Photosynthesis
Peat
Decomposers
Carbonate
Plant and animal wastes
Coal
Oil and Gas
FIGURE 1.16
Schematic representation of the global carbon cycle.
respiration. In addition to the uptake of CO2 via photosynthe­
sis, marine organisms also use carbon for calcium carbon­
ate (CaCO3) to make hard, protective shells. Furthermore,
decomposer organisms (e.g., bacteria) act on the remains of
dead plants and animals, releasing CO2 to the atmosphere
and ocean through cellular respiration.
When marine organisms die, their remains
(shells and skel­etons) slowly settle downward through
ocean waters. In time, these organic materials reach
the sea floor, accumulate, are compressed by their own
weight and the weight of other sediments, and gradually
transform into solid, carbonate rock. Common carbonate
rocks are limestone (CaCO3) and dolostone (CaMg(CO3)2).
Subsequently, tectonic processes uplift these marine
rocks and expose them to the atmosphere and weather­ing
processes. Rainwater contains dissolved atmospheric CO2
producing carbonic acid (H2CO3) that, in turn, dissolves
carbonate rock releasing CO2. As part of the global water
Chapter 1 Climate Science for Today’s World
cycle, rivers and streams trans­port these weathering
products to the sea where they settle out of suspension
or precipitate as sediments that accumu­late on the ocean
floor. Over the millions of years that constitute geologic
time, the formation and ultimate weathering and erosion
of carbon-containing rocks have significantly altered the
concentration of carbon dioxide in the atmosphere thereby
changing the climate.
From about 280 to 345 million years ago, the
geologic time interval known as the Carboniferous period,
trillions of metric tons of organic remains (detritus) accu­
mulated on the ocean bottom and in low-lying swampy
terrain on land. The supply of detritus was so great that
decom­poser organisms could not keep pace. In some marine
envi­ronments, plant and animal remains were converted to
oil and natural gas. In swampy terrain, heat and pressure
from accumulating organic debris concentrated carbon,
convert­ing the remains of luxuriant swamp forests into
thick layers of coal. Today, when we burn coal, oil, and
natural gas, collectively called fossil fuels, we are tapping
energy that was originally locked in vegetation through
photosynthe­sis hundreds of millions of years ago. During
combustion, carbon from these fossil fuels combines with
oxygen in the air to form carbon dioxide which escapes to
the atmosphere.
Another important biogeochemical cycle operat­
ing in the Earth system is the global water cycle (Chapter
5), which is closely linked to all other biogeochemical
cycles. Reservoirs in the water cycle (hydrosphere,
atmosphere, geosphere, biosphere) are also reservoirs
in other cycles, for which water is an essential mode
of transport. In the nitrogen cycle, for example, intense
heating of air caused by lightning combines atmospheric
nitrogen (N2), oxygen (O2), and moisture to form droplets
of extremely dilute nitric acid (HNO3) that are washed
by rain to the soil. In the process, nitric acid converts
to nitrate (NO3-), an important plant nutrient that is
taken up by plants via their root systems. Plants convert
nitrate to ammonia (NH3), which is incorporated into a
variety of compounds, including amino acids, proteins,
and DNA. On the other hand, both nitrate and ammonia
readily dissolve in water so that heavy rains can deplete
soil of these important nutri­ents and wash them into
waterways.
The components of Earth’s climate system coevolved through geologic time. For more on this topic,
refer to this chapter’s first Essay. At times in the past,
Earth’s climate underwent massive changes that brought
about large-scale extinctions of plants and animals. For
more on this, see this chapter’s second Essay.
21
The Climate Paradigm
The climate system determines Earth’s climate as the
result of mutual interactions among the atmosphere,
hydrosphere, cryosphere, geosphere, and biosphere
and responses to external influences from space. As
the composite of prevailing weather patterns, climate’s
complete description includes both the average state of the
atmosphere and its variations. Climate can be explained
primarily in terms of the complex redistribution of heat
energy and matter by Earth’s coupled atmosphere/ocean
system. It is governed by the interaction of many factors,
causing climate to differ from one place to another and to
vary on time scales from seasons to millennia. The range
of climate, including extremes, places limitations on living
organisms and a region’s habitability.
Climate is inherently variable and now appears
to be changing at rates unprecedented in relatively recent
Earth history. Human activities, especially those that alter
the composition of the atmosphere or characteristics of
Earth’s surface, play an increasingly important role in
the climate system. Rapid climate changes, natural or
human-caused, heighten the vulnerabilities of societies
and ecosystems, impacting biological systems, water
resources, food production, energy demand, human health,
and national security. These vulnerabilities are global to
local in scale, and call for increased understanding and
surveillance of the climate system and its sensitivity to
imposed changes. Scientific research focusing on key
climate processes, expanded monitoring, and improved
modeling capabilities are already increasing our ability
to predict the future climate. Although incomplete, our
current understanding of the climate system and the farreaching risks associated with climate change call for the
immediate preparation and implementation of strategies
for sustainable development and long-term stewardship of
Earth.2
Conclusions
Climate can be defined in terms of empirically derived
statistical summaries based on the instrument record,
specifying mean, median and extreme values of various
climatic elements such as temperature and precipitation.
Alternately, climate can be defined in terms of the
dynamic forces that shape the climate system and its
spatial and temporal variability. These two definitions
For a timeline of key historical events in climate science, see
Appendix II.
2
22
Chapter 1 Climate Science for Today’s World
of climate (empirical and dynamic) are actually two
sides of the same coin and both are utilized in our study
and application of climate science (Figure 1.17). Our
primary motivation for studying climate science is the
link between climate and society. Society influences
and is influenced by climate. By developing our basic
understandings of climate science, we position ourselves
to better understand the public policy and economic
dimensions of climate change. In this chapter, we have
seen that a central concept in this understanding is the
climate system and the interaction of its component
subsystems. In the next chapter, we continue building
our climate science framework with a focus on spatial
and temporal scales of climate, interactions of climate
elements, climate models, and monitoring of the climate
system.
Basic Understandings
•
•
•
•
Climate
Empirical
Dynamic
Normals,
means and
extremes
Boundary
conditions
•
Climate system
Atmosphere
Hydrosphere
Cryosphere
Geosphere
Biosphere
•
Climate
variability
Climate
change
Temporal / Spatial
Natural / Anthropogenic
FIGURE 1.17
This flow chart identifies the major components of our framework
for studying climate science.
•
The study of Earth’s climate began with the
ancient Greek philosophers and geographers.
The first climate classification, devised by
Parmenides in the 5th century BCE, was based on
latitudinal variations in sunshine that accompany
regular changes in the angle of inclination of the
Sun.
Weather is defined as the state of the atmosphere
at some place and time, described in terms of
such variables as temperature, humidity, and
precipitation. Meteorology is the study of the
atmosphere, processes that cause weather, and
the life cycle of weather systems.
One definition of climate is empirical (based
on statistical summaries) whereas another is
dynamic (incorporating the governing forces).
The first describes a climate state, while the
second seeks to explain climate.
With the empirical definition, climate is weather
at some locality averaged over a specified time
period plus extremes in weather during the same
period. By international convention, normals of
climatic elements are computed for a 30-year
period beginning with the first year of a decade.
At the close of the decade, the averaging period is
moved forward 10 years. The 30-year averaging
period of 1971-2000 is the reference for the first
decade of the 21st century.
With the dynamic definition, climate encompasses
the boundary conditions in the planetary system
(that is, the planetary system). These boundary
conditions select the array of weather patterns that
characterize each of the seasons. Climatology is
the study of climate, its controls, and spatial and
temporal variability.
The climatic norm or normal often is equated
to the average value of some climatic element
such as temperature over a defined 30-year
interval. More precisely, the climatic norm of
some locality encompasses the total variation
in the climate record, that is, both averages plus
extremes. Establishing representative norms
goes beyond arithmetical averages as the mean
value of a climatic element may not be the same
as the median value.
In the second decade of the 19th century, the
Army Medical Department was first to establish
a national network of weather and climate
Chapter 1 Climate Science for Today’s World
•
•
•
•
•
•
observing stations. By the mid-1800s, Joseph
Henry formed a national network of volunteer
citizen observers who mailed monthly weather
reports to the Smithsonian. Invention of the
electric telegraph enabled Henry to obtain
simultaneous weather reports and to draw the
first weather maps.
On 1 November 1870, the U.S. Army Signal
Corps began operating a telegraph-linked storm
warning network for the Great Lakes. Soon the
network spread to other parts of the nation and
encompassed networks operated by the Army
Medical Department, the Smithsonian, and
others. The Signal Corps was the predecessor to
the U.S. Weather Bureau and today’s National
Weather Service (NWS).
Derived from the old weather/climate networks
operated by the Army Medical Department,
the Smithsonian Institution, and the Army
Signal Corps is the NWS Cooperative Observer
Network. More than 11,000 volunteers record
daily precipitation and maximum/minimum
temperature for climatic, hydrologic, and
agricultural purposes.
Climate provides resources that can be exploited
to the benefit of society as well as imposing
constraints on social and economic development.
It is not possible to weather- or climate-proof
society to prevent damage to life and property. In
the agricultural sector of the developed world, the
prevailing strategy is to depend on technology to
circumvent climate constraints.
Human activity is influencing climate with
significant consequences for society. In addition,
some human activities are making society and
ecosystems more vulnerable to climate change.
Examples include the rapid growth of human
population in the coastal zone and the migration
of people to areas that are climatically marginal
for agriculture.
An important consideration regarding weather
and climate extremes is societal resilience, that is,
the ability of a society to recover from a weatheror climate-related or other natural disaster.
Assessment of societal resilience must consider
the regional bias of severe weather and climate
extremes and the technological capabilities of a
given society.
A system is an entity whose components interact
in an orderly way according to natural laws.
•
•
•
•
•
•
•
23
Earth’s climate system consists of the following
interacting subsystems: atmosphere, hydrosphere,
cryosphere, geosphere and biosphere.
Earth’s atmosphere is a relatively thin envelope
of gases and tiny suspended solid and liquid particles (aero­sols) surrounding the solid planet.
Based on the average vertical temperature profile,
the atmosphere is divided into the troposphere,
stratosphere, mesosphere, and thermosphere.
The lowest layer, the troposphere, is where most
weather occurs and where the atmosphere interfaces with the other subsystems of the climate
system.
Nitrogen (N2) and oxygen (O2), the principal
atmo­spheric gases, are mixed in uniform
proportions up to an altitude of about 80 km
(50 mi). Not counting water vapor (which has a
highly variable concentration), ni­trogen occupies
78.08% by volume of the lower atmo­sphere and
oxygen is 20.95% by volume.
The significance of atmospheric gases and aerosols
is not necessarily related to their concentration.
Some atmospheric components that are essential
for life oc­cur in very low concentrations.
Examples are water vapor (needed for the global
water cycle), carbon dioxide (for photosynthesis),
and stratospheric ozone (protection from solar
ultraviolet radiation).
The atmosphere is dynamic and circulates in
response to temperature gradients that arise from
differences in rates of radia­tional heating and
radiational cooling within the land-atmosphereocean system.
The hydrosphere consists of water in all three
phases (solid, liquid, and vapor) that continually
cycles among reservoirs in the planetary
system. The ocean is the largest reservoir in the
hydrosphere, con­taining 97.2% of all water on the
planet and covering 70.8% of Earth’s surface.
The ocean features wind-driven surface currents
and density-driven deep currents caused by
small dif­ferences in temperature and salinity. An
important control of climate is the meridional
overturning circulation (MOC).
The hydrosphere is dynamic, with water flowing
at dif­ferent rates through and between different
reservoirs within the climate system. The time
required for water to reach the ocean varies from
days to weeks in river channels and through
millennia for water locked in glacial ice sheets.
24
Chapter 1 Climate Science for Today’s World
•
•
•
•
In addition to the Antarctic and Greenland ice
sheets, the frozen portion of Earth’s hydrosphere,
called the cryosphere, encompasses mountain
glaciers, perma­frost, sea ice (frozen seawater),
and ice bergs.
The geosphere is the solid portion of the planet
com­posed of rocks, minerals, soils and sediments.
The rigid uppermost portion of Earth’s mantle
plus the overly­ing crust, constitutes Earth’s
lithosphere. Surface geo­logical processes (i.e.,
weathering and erosion) and internal geological
processes (i.e., mountain building, volcanic
eruptions) continually modify the lithosphere.
Weathering refers to the physical and chemical
break­down of rock into sediments. Agents of
erosion (i.e., riv­ers, glaciers, wind) remove,
transport, and subsequently deposit sediments.
Plate tectonics is responsible for the slow
movement of continents across the face of the
Earth, mountain building, and volcanism. These
processes can explain climate change operating
over hundreds of millions of years.
The biosphere encompasses all life on Earth and is
dominated on land and in the ocean by bacteria and
single-celled plants and animals. Photosynthesis
and cellular respiration are processes that are
essential for life where sunlight is available and
exemplify the interaction of the biosphere with the
other sub­systems of the climate system.
•
•
•
•
•
The biosphere is com­posed of ecosystems,
communities of plants and animals that interact
with one another, together with the physical
conditions and chemical substances in a spe­
cific geographical area. Ecosystems consist of
pro­ducers (plants), consumers (animals), and
decompos­ers (bacteria, fungi). These organisms
occupy different (ascending) trophic levels in
food chains.
Climate is the principal ecological control,
largely determining the location and species
composition of natural ecosystems such as
deserts, rain forests, and tundra.
Biogeochemical cycles are pathways along which
solids, liquids, or gases flow among the various
reservoirs within subsystems of the planetary
system.
Bio­geochemical cycles follow the law of energy
conservation, which states that energy is neither
created nor destroyed although it is converted
from one form to another. Biogeochemical
cycles also follow the law of conservation of
matter, which states that matter can neither be
created nor destroyed, but can change chemical
or physical form.
The time required for a unit mass of some
sub­stance to cycle into and out of a reservoir
is the resi­dence time of the substance in the
reservoir.
Enduring Ideas
• The empirical definition of climate is based on statistical summaries of climatic elements
whereas the dynamic definition incorporates the boundary conditions in the planetary system
coupled with typical seasonal weather patterns.
• The climatic norm encompasses the total variability in the climate record, that is, both
averages plus extremes in weather.
• Earth’s climate system consists of the atmosphere, hydrosphere, cryosphere, geosphere, and
biosphere that are linked by biogeochemical cycles.
• Climate imposes constraints on social and economic development by governing such
essentials as fresh water supply and energy needs for space heating and cooling.
Chapter 1 Climate Science for Today’s World
25
Review
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Provide some examples of how climate operates as the principal environmental control.
Define weather and explain why a place and time must be specified when describing the weather.
How does the empirical definition of climate differ from the dynamic definition of climate?
Define what is meant by the climatic norm.
How does the operational weather observing network compare with the cooperative observer network in terms
of types of data collected?
Identify some of the linkages between climate and society.
What is the significance of Earth’s troposphere?
Under what climatic conditions would a glacier form?
What is the basic composition and structure of Earth’s geosphere?
Distinguish between photosynthesis and cellular respiration. What role do these two processes play in the global
carbon cycle?
Critical Thinking
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Identify two climate controls that operate external to the land-atmosphere-ocean system.
In describing the climate of some locality, of what value is the record of weather extremes?
What are some disadvantages of computing averages of climatic elements based on a 30-year period?
In a study of climate change, why is it preferable to consider climate records only from stations that have not
relocated?
Provide some examples of how the significance of an atmospheric gas is not necessarily related to its
concentration.
Speculate on how a glacial ice sheet influences the climate.
What roles might plate tectonics and volcanic eruptions play in climate change?
How does the law of energy conservation apply to biogeochemical cycles?
In a biogeochemical cycle, what is the relationship between cycling rates and residence time?
What roles are played by water in biogeochemical cycles?
26
Chapter 1 Climate Science for Today’s World
Chapter 1 Climate Science for Today’s World
27
ESSAY: Evolution of Earth’s Climate System
The components of Earth’s climate system (atmosphere, hydrosphere, cryosphere, geosphere, and biosphere) co-evolved
through the vast expanse of Earth history. According to astronomers, more than 4.5 billion years ago, Earth, the Sun, and the
entire solar system evolved from an immense rotating cloud of dust, ice and gases, called a nebula (Figure 1). Temperature,
density, and pressure were highest at the center of the nebula, gradually decreasing toward its outer limits. Extreme conditions
at the nebula’s center vaporized ice and light elements and drove them toward the nebula’s outer reaches. Consequently,
residual dry rocky masses formed the inner planets (including Earth). Farther out, meteorites and the less-dense giant planets
Saturn and Jupiter formed.
FIGURE 1
The leftmost “pillar” of interstellar hydrogen gas and dust in M16, the Eagle Nebular. [Courtesy of NASA/NSSDC Photo Gallery]
Earth is known as the water planet—ocean water covers almost 71% of its surface. Yet, in view of how the solar system
is believed to have formed, it is surprising that even that much water is present on Earth. Where did the hydrosphere come
from? Scientists do not have a complete explanation but a popular hypothesis attributes water on Earth to the bombardment
of the planet by comets and/or planetesimals, large meteorites a few kilometers across. While meteorites are about 10% ice
by mass and the giant planets contain some ice, most of the water in the nebula condensed in comets at distances beyond
Saturn and Jupiter. A comet is a relatively small mass composed of meteoric dust and ice that moves in a parabolic or highly
elliptical orbit around the Sun.
Comets are about half ice. During the latter stages of Earth’s formation, comets impacted the planet’s surface
forming a veneer of water. Jupiter’s strengthening gravitational attraction may have drawn a multitude of ice-rich comets
from the outer to the inner reaches of the solar system on a collision course with Earth. This hypothesis remained popular until
scientists discovered that water on Earth and ice in comets are not chemically equivalent. Spectral analyses of three comets
that approached Earth in recent years revealed that comet ice contains about twice as much deuterium as the water on Earth.
Deuterium is an isotope of hydrogen whose nucleus is composed of one proton plus one neutron and is very rare on Earth;
a normal hydrogen atom consists of a single proton. Based on this finding, some scientists suggest that comets accounted
for no more than half the water on Earth and perhaps much less. The water in planetesimals, on the other hand, contains less
deuterium than comet ice; they may have impacted Earth during the latter stages of the planet’s formation. However, the
28
Chapter 1 Climate Science for Today’s World
ratio of some other chemical components of planetesimals is not the same as the ratio of those components on Earth. Another
possibility is that Earth’s water is indigenous; that is, the center of the nebula may have been cooler than previously assumed
and some of the materials present in the inner solar system that formed Earth were water-rich.
In the beginning, Earth’s atmosphere probably was mostly hydrogen (H2) and helium (He) plus some hydrogen
compounds, including methane (CH4) and ammonia (NH3). Because these atoms and molecules are relatively light and have
high molecular speeds, Earth’s weak gravitational field plus high temperatures allowed this early atmosphere to escape to
space. In time, however, volcanic activity began spewing huge quantities of lava, ash, and gases. By about 4.4 billion years
ago, the strength of the planet’s gravitational field was sufficient to retain a thin gaseous envelope of volcanic origin, Earth’s
primeval atmosphere.
The principal source of Earth’s atmosphere was outgassing from the geosphere, that is, the release of gases from
rock through volcanic eruptions and the impact of meteorites on the planet’s rocky surface. Perhaps as much as 85% of all
outgassing took place within a million or so years of the planet’s formation while outgassing continues to this day, although
at a slower pace. The primeval atmosphere was mostly carbon dioxide, with some nitrogen (N2) and water vapor (H2O),
along with trace amounts of methane, ammonia, sulfur dioxide (SO2), and hydrochloric acid (HCl). Radioactive decay of an
isotope of potassium in the planet’s bedrock added argon (Ar), an inert (chemically non-reactive) gas, to the evolving mix
of atmospheric gases. Dissociation of water vapor into its constituent atoms, hydrogen and oxygen, by high-energy solar
ultraviolet radiation contributed a small amount of free oxygen to the primeval atmosphere. (The lighter hydrogen—with its
relatively high molecular speeds—escaped to space.) Also, some oxygen combined with other elements in various chemical
compounds, such as carbon dioxide.
Scientists suggest that between 4.5 and 2.5 billion years ago, the Sun was about 30% fainter than it is today. This did
not mean a cooler planet, however, because the atmosphere was 10 to 20 times denser than the present one. Carbon dioxide
slows the escape of Earth’s heat to space, contributing to average surface temperatures that were as high as 85 °C to 110 °C
(185 °F to 230 °F), levels significantly higher than currently observed (approximately 15 °C or 59 °F).
By 4 billion years ago, the planet began to cool and the Earth system underwent major changes. Cooling caused
atmospheric water vapor to condense into clouds that produced rain. Precipitation plus runoff from landmasses gave rise
to the ocean that eventually covered as much as 95% of the planet’s surface. The global water cycle (which helped cool
the Earth’s surface through evaporation) and its largest reservoir (the ocean) were in place. Rains also helped bring about a
substantial decline in the concentration of atmospheric CO2. As noted elsewhere in this chapter, CO2 dissolves in rainwater,
producing weak carbonic acid that reacts chemically with bedrock. The net effect of this large-scale geochemical process was
increasing amounts of carbon chemically locked in rocks and minerals with less and less CO2 remaining in the atmosphere.
The physical and chemical breakdown of rock (weathering) plus erosion on land delivered some carbon-containing sediment
to the ocean. Also, rains washed dissolved CO2 directly into the sea, and some atmospheric CO2 dissolved in ocean water as
sea surface temperatures fell. (Carbon dioxide is more soluble in cold water.)
Although CO2 has been a minor component of the atmosphere for at least 3.5 billion years, its concentration has
fluctuated during the geologic past, with important implications for global climate and life on Earth. All other factors being
equal, more CO2 in the atmosphere means an enhanced greenhouse effect and higher temperatures near Earth’s surface. From
about 5000 ppm about 550 million years ago, the concentration of atmospheric CO2 generally declined. However, many
episodes of large-scale volcanic activity were responsible for temporary upturns in CO2 concentration and a considerably
warmer global climate. These peaks in atmospheric CO2 correspond in time with most major mass extinctions of plant and
animal species on land and in the ocean (discussed in this chapter’s second Essay).
During the Pleistocene Ice Age (1.7 million to 10,500 years ago), atmospheric CO2 levels also fluctuated, decreasing
during episodes of glacial expansion and increasing during episodes of glacial recession (although it is not clear whether
variations in atmospheric CO2 were the cause or effect of these global-scale climate changes).
The biosphere also played an important role in Earth’s evolving atmosphere, primarily through photosynthesis,
the process whereby green plants use sunlight, water, and CO2 to manufacture their food. A byproduct of photosynthesis is
oxygen (O2). Although vegetation is also a sink for CO2, photosynthesis probably was not as important as the geochemical
processes described earlier in removing CO2 from the atmosphere. Based on the fossil record, photosynthesis dates to about
2.7 billion years ago, with the first appearance of cyanobacteria in the ocean. However, it was not until 2.5 to 2.4 billion years
ago that the atmosphere became oxygen-rich. Although oxygen was produced for 200-300 million years, none accumulated
in the atmosphere. Why the lengthy delay?
Chapter 1 Climate Science for Today’s World
29
Apparently, the ocean and land took up oxygen as fast as it was produced. In the ocean, most oxygen combined
with marine sediments while very little entered the atmosphere. Eventually, oxidation of marine sediments tapered off
and photosynthetic oxygen dissolved in ocean water. According to findings reported in 2007 by researchers Lee Kump of
Pennsylvania State University and M. Barley of the University of Western Australia, the geologic record indicates a shift in
geologic activity about 2.5 billion years ago from underwater volcanism to terrestrial volcanism. This shift was accompanied
by a change in the composition of the eruptive gases, from those that react with oxygen to those that do not react with oxygen.
With the subsequent build-up of atmospheric oxygen, and the concurrent decline in atmospheric CO2, oxygen became the
second most abundant atmospheric gas within the next 500 million years.
With oxygen emerging as a major component of Earth’s atmosphere, the ozone shield formed. Within the stratosphere,
incoming solar ultraviolet (UV) radiation drives reactions that convert oxygen to ozone (O3) and ozone to oxygen. Absorption
of UV radiation in these reactions prevents potentially lethal intensities of UV radiation from reaching Earth’s surface. By
about 440 million years ago, formation of the stratospheric ozone shield made it possible for organisms to live and evolve on
land. UV radiation does not penetrate ocean water to any great depth, so marine life was able to exist in the ocean depths prior
to the formation of the ozone shield. With the ozone shield, marine life was able to thrive in surface waters, and eventually
on land.
During the past 550 million years, the concentration of oxygen in the atmosphere has fluctuated significantly. These
fluctuations were linked to imbalances in the rates of the weathering of organic carbon and pyrite (FeS2), which decreases
atmospheric oxygen, and the sedimentation of these materials, which increases atmospheric oxygen. Over the 550-millionyear period, the percentage of O2 in the atmosphere has been estimated to have varied between about 13% and 31%; at present
oxygen is about 21% of the air we breathe.
Nitrogen (N2), a product of outgassing, became the most abundant atmospheric gas because it is relatively inert and
its molecular speeds are too slow to readily escape Earth’s gravitational pull. Furthermore, compared to other atmospheric
gases, such as oxygen and carbon dioxide, nitrogen is less soluble in water. All these factors greatly limit the rate at which
nitrogen cycles out of the atmosphere. While nitrogen continues to be generated as a minor component of volcanic eruptions,
today the principal natural source of free nitrogen entering the atmosphere is denitrification, which accompanies the bacterial
decay of plants and animals. This input is countered by nitrogen removed from the atmosphere by biological fixation (i.e.,
direct nitrogen uptake by leguminous plants such as clover and soybeans) and atmospheric fixation (i.e., the process whereby
the high temperatures associated with lightning causes nitrogen to combine with oxygen to form nitrates that are washed by
rains to Earth’s surface).
In summary, during the more than 4.5 billion years since Earth’s formation, the planet’s climate system evolved
gradually. Bombardment of Earth by comets and/or large meteorites delivered the water of the hydrosphere. Outgassing from
the geosphere was the origin of most atmospheric gases. Geochemical processes, photosynthesis, the stratospheric ozone
shield, and biogeochemical cycles explain climatically-significant fluctuations in the chemistry of the atmosphere.
30
Chapter 1 Climate Science for Today’s World
ESSAY: Asteroids, Climate Change, and Mass Extinctionsa
Geologists and other scientists have gathered evidence from the fossil record of five major mass extinctions that occurred
over the past 550 million years (Table 1). Elimination of 50% or more of all species indicates drastic changes in Earth’s
environment, which exceeded the tolerance limits of a vast number of organisms. What caused these mass extinctions?
TABLE 1
Major Mass Extinctions of Plant and Animal Species over the
past 550 Million Years
End of Ordovician period
End of Devonian period
End of Permian period
End of Triassic period
Cretaceous-Tertiary boundary
443 million years ago
374 million years ago
251 million years ago
201 million years ago
65 million years ago
Prior to 1980, the most popular explanation for mass extinctions was a gradual decrease in species number (perhaps
over millions of years) due to long-term climate change coupled with ecological forces. In 1980, however, another much
more dramatic explanation took center stage. The father-son team of scientists Luis (1911-1988) and Walter (1940- ) Alvarez
of the University of California, Berkeley, proposed that an asteroid impact on Earth was responsible for the mass extinction
that took place 65 million years ago. This event was known as the K-T mass extinction, named for the boundary between the
Cretaceous and Tertiary periods of geologic time. The Alvarez team presented convincing evidence of an asteroid impact,
including the discovery of iridium (Ir) in sedimentary layers from around the world—all dating from 65 million years ago.
Iridium is a silver-gray metallic element that is extremely rare in Earth’s crust. Asteroids, however, contain a much higher
concentration of iridium. The Alvarez hypothesis was bolstered by features found within and near the impact site.
The K-T asteroid produced the Chicxulub crater, a 180-km (112-mi) wide crater on the floor of the ancient Caribbean
Sea (Figure 1). Marine sediments gradually filled the crater and geological forces later elevated a portion of the crater above
FIGURE 1
The Chicxulub Crater, centered near the town of Chicxulub
on Mexico’s Yucatán Peninsula, is about 180 km (112 mi) in
diameter, represented here as gravity and magnetic field data.
It formed about 65 million years ago when a mountain-size
asteroid (at least 10 km or 6 mi across) struck Earth’s surface.
The effects of the impact were thought to be responsible for
the extinction of the dinosaurs and about 70% of all species
then living on the planet. [Courtesy of NASA, Lunar Planetary
Institute, V.L. Sharpton]
______________
For much more on this topic, see Ward, Peter D., 2007. Under A Green Sky. Washington, DC: Smithsonian Books, 242 p.
a
Chapter 1 Climate Science for Today’s World
31
sea level. Today, what remains of the Chicxulub crater forms part of Mexico’s Yucatán Peninsula. Radar images obtained by
the Space Shuttle Endeavour in 2000 revealed a 5-m (16-ft) deep, 5-km (3-mi) wide trough on the Yucatán Peninsula that may
mark the outer rim of the crater. Drilling through the layers of sediment on the floor of the nearby Gulf of Mexico recovered
cores of fractured and melted rock from the impact zone.
Other evidence of the asteroid impact consists of bits of tiny bead-like spherules of glassy rock, which originated as
droplets of molten rock blasted into the atmosphere by the impact. These droplets cooled as they fell through the atmosphere
onto the land or into the ocean. They were recovered from nearby deep-ocean sediments. Many rocks on land contain mineral
grains deformed by the extreme heat and pressure produced by the impact (e.g., shocked quartz). Unusual sediment deposits
were produced by enormous waves (tsunamis) generated when the asteroid (at least 10 km or 6 mi in diameter) struck the
ocean surface. In addition, a layer of soot indicates considerable burning vegetation on land.
The K-T asteroid impact had a catastrophic effect on life. Best known is the extinction of the dinosaurs, which had
dominated life on Earth for more than 250 million years. Dinosaurs were not the only victims, however. The asteroid impact
destroyed more than 50% of the other life forms then existing on the planet and caused major extinctions among many groups
of marine organisms, including plankton.
What precisely caused this ecological disaster? One widely accepted theory is that the asteroid impact vaporized
large amounts of sulfur-containing deep-sea sediments. This sulfur was blown into the atmosphere, where it generated
enormous clouds of tiny sulfate particles, likely augmented by meteoric and Earth materials also thrown into the atmosphere
by the impact. These clouds greatly reduced the sunlight reaching Earth’s surface for 8 to 13 years; most plants died because
they could not photosynthesize. Furthermore, precipitation decreased by up to 90%. In this dark, cold and dry environment,
dinosaurs and other animals that depended on plants for food starved and the carnivores that fed on them followed. Only small
animals (as some mammals) could survive by eating the dead plants and animals until conditions improved and new food
sources became available. Eventually, the aerosols settled out of the atmosphere, and photosynthesis resumed when dormant
seeds sprouted. Small mammals evolved rapidly to take the place of the dinosaurs.
Another possibility is that red-hot, impact-generated particles rained down through the atmosphere making it so hot
that most plants and animals were killed directly.
In the 1980s and 1990s, the Alvarez theory of asteroid impact was widely accepted as the cause of all but one of
the five major mass extinctions (Table 1). However, a vocal minority of scientists took exception to the preeminent role
of asteroid impact, arguing that many of the major mass extinctions were linked to volcanic activity and increased levels
of atmospheric CO2. The largest eruptions of flood basalts closely correspond in age to the times of most major mass
extinctions. Flood basalts consist of many successive lava flows erupting from fissures in Earth’s crust, and accompanied
by toxic gases released into the atmosphere, including hydrogen sulfide (H2S), and the greenhouse gases carbon dioxide
and methane (CH4).
Flood basalt eruptions can be enormous. The world’s largest flood basalt eruptions (that produced the Siberian Traps)
delivered about 4.2 million km3 (1 million mi3) of lava over an area of nearly 7.8 million km2 (3 million mi2) approximately
252 to 248 million years ago. This eruption was very near the time of the great Permian mass extinction (around 250 million
years ago), when 90% of all ocean species and 70% of terrestrial vertebrates on Earth were wiped out. No evidence of an
asteroid impact has been found to explain the Permian extinction. In addition, most mass extinctions took place during times
when the concentration of atmospheric CO2 was relatively high or rapidly rising.
By 2005, a new hypothesis was firmly in place that attributed most major mass extinctions to a combination of
chemical and circulation changes in the ocean, coupled with global warming due to an enhanced greenhouse effect. In
arriving at this alternate explanation for mass extinctions, scientists relied on analysis of biomarkers where fossils were
absent. Biomarkers are the organic chemical residue of organisms extracted from ancient strata.
According to research conducted by Lee Kump and his colleagues at Pennsylvania State University, the late Permian
ocean was stratified. The bottom water had little or no dissolved oxygen while the shallow surface layer was oxygenated.
(Most of today’s ocean is oxygenated from top to bottom.) With the release of greenhouse gases to the atmosphere during
the eruptions that produced the Siberian Traps, the global temperature rose dramatically. This warmed the surface ocean
waters, reducing the amount of oxygen absorbed from the atmosphere. A reduction in the equator to pole temperature gradient
caused a weakening of wind and wind-driven surface ocean currents. Consequently, the ocean circulation changed so that
great volumes of warm, nearly oxygen-free water filled the ocean bottom. In this environment, microbes were dominated by
anaerobic bacteria that consumed sulfur and produced hydrogen sulfide. Biomarkers of green sulfur bacteria and photosynthetic
32
Chapter 1 Climate Science for Today’s World
purple sulfur bacteria were extracted from strata of this age. In time the layer of oxygen-poor, H2S-rich water became thicker
and reached the ocean surface where it escaped to the atmosphere. Highly toxic, especially at high temperatures, H2S also
reacts with and destroys stratospheric ozone, allowing lethal levels of solar ultraviolet radiation to reach Earth’s surface thus
causing the end of the Permian era.
THE NATIONAL SCIENCE
EDUCATION STANDARDS
AND DATASTREME ECS
——————————————
The National Science Education Standards (NSES) are
intended to improve science education in the K-12
schools by redirecting and upgrading efforts in six component areas:
•
•
•
•
•
•
Science Teaching
Professional Development for Teachers of Science
Assessment in Science Education
Science Content
Science Education Program
Science Education System
DataStreme Earth's Climate System (ECS), a teacherdevelopment program of the American Meteorological
Society's education office in Washington, DC, addresses
specific aspects of standards proposed for each of these
components. Central to the Project is a distance-learning
course in which teachers explore the basics of climate
science using an Earth system science perspective.
Teachers access the DataStreme ECS website and download climate-related data formatted for teaching purposes
and coordinated with investigations having significant
scientific and pedagogical content. Investigations have
both printed and real-time components and are delivered
via the website. Background information is provided by
the DataStreme ECS textbook.
DataStreme ECS includes the following aspects of
standards proposed for the six NSES components. Page
references are in National Science Education Standards
(National Research Council, Washington, DC: National
Academy Press, 1996).
Science Teaching
________________________________
•
Teachers of science plan an inquiry-based science
program for their students. In doing this, teachers....select science content and adapt and design
curricula to meet the interests, knowledge, understanding,
abilities,
and
experiences
of
students,....work together as colleagues within and
across disciplines and grade levels. [p. 30]
DataStreme ECS focuses on a content area that appeals to just about everyone because of the influence of
the climate on daily life. Students (and most teachers)
are typically very receptive to computer-delivered information. DataStreme ECS alumni agree to act as their
school’s climate studies resource person and thereby they
work with colleagues in other grades and subjects.
DataStreme ECS alumni have already demonstrated how
current climate information can be used to spur student
interest in many subjects including science, mathematics,
geography, writing, and the use of technology.
•
Teachers of science guide and facilitate learning. In
doing this, teachers....focus and support inquiries
while interacting with students,....orchestrate discourse
among
students
about
scientific
ideas,....encourage and model the skills of scientific
inquiry, as well as the curiosity, openness to new
ideas and data, and skepticism that characterize science. [p. 32]
DataStreme ECS provides teachers with an opportunity to develop confidence in using an online data
delivery system in their classroom to explore/confirm
scientific concepts and data, some of which may have
societal implications (e.g., sea level rise, increasing
greenhouse effect). Students, individually or in teams,
may be assigned to download climatology products, analyze data, and report on their scientific meaning and
significance. Furthermore, the subject matter of the
DataStreme ECS course is at the heart of many controversial environmental issues (e.g., global climate change,
energy issues) that will serve as a catalyst for student
discussion. DataStreme ECS promotes the involvement
of parents in the education of their children: Students are
encouraged to share with their parents near real-time climate information and together to work on investigations.
•
•
Teachers of science design and manage learning
environments that provide students with the time,
space, and resources needed for learning science.
In doing this, teachers....make the available science
tools, materials, media, and technological resources
accessible to students,...identify and use resources
outside the school.
[p. 43]
Through DataStreme ECS, teachers gain experience
and confidence in accessing the Internet for delivery of
scientifically-sound environmental data and investigations. This experience and confidence--coupled with an
understanding of their students' needs and abilities-enable them to adapt what they have learned for use in
their classrooms. DataStreme ECS resources, developed
and tested by professional scientists and science educators, are available to participants both during and
subsequent to their enrollment in the course. DataStreme
ECS links the classroom to climate events taking place in
near real-time around the world.
•
Professional Development for
Teachers of Science
________________________________
Teachers of science actively participate in the ongoing planning and development of the school science
program. In doing this, teachers....participate fully
in planning and implementing professional growth
and development strategies for themselves and their
colleagues. [p. 51]
DataStreme ECS alumni agree to act as their
school’s climate studies resource person. Guidance materials are supplied to them so that they can conduct peer
training sessions for their colleagues both on the DataStreme ECS online delivery system and selected climate
topics. Of special interest is the introduction of climate
information across the curriculum and at different grade
levels.
Professional development for teachers of science
requires learning essential science content through
the perspectives and methods of inquiry. Science
learning experiences for teachers must involve
teachers in actively investigating phenomena that
can be studied scientifically, interpreting results,
and making sense of findings consistent with currently accepted scientific understanding,....address
issues, events, problems, or topics significant in science and of interest to participants....introduce
teachers to scientific literature, media, and technological resources that expand their science
knowledge and their ability to access further
knowledge....build on teacher’s current science understanding, ability, and attitudes....encourage and
support teachers in efforts to collaborate. [p. 59]
DataStreme ECS is a teacher development program.
Participants learn the basics of climate science by investigating climate-related topics in near real-time, that is,
by interpreting near real-time climate data, maps and
charts, and remotely sensed images. DataStreme ECS
employs a constructivist approach to scientific inquiry,
that is, participants interact with electronically-delivered
learning materials and their Local Implementation Team
(LIT) mentor to negotiate understanding. In addition,
participants have weekly assignments in the DataStreme
ECS textbook that helps direct and broaden their
knowledge of climate concepts. DataStreme ECS directs
teachers to other scientific resources, many of which are
available on the Web.
•
Professional development for teachers of science
requires integrating knowledge of science, learning,
pedagogy, and students; it also requires applying
that knowledge to science teaching. Learning experiences for teachers of science must connect and
integrate all pertinent aspects of science and science
education....use inquiry, reflection, interpretation of
research, modeling, and guided practice to build
understanding and skill in science teaching. [p. 62]
Designers of DataStreme ECS were very much
aware of the need to assist participating teachers in
adapting what they have learned to classroom teaching. Hence, investigations include pedagogical
components.
•
Professional development for teachers of science
requires building understanding and ability for lifelong learning. Professional development activities
must support the sharing of teacher expertise by
preparing and using mentors, teacher advisers,
coaches, lead teachers, and resource teachers to
provide professional development opportunities....provide opportunities to know and have access
to
existing
research
and
experiential
knowledge....provide opportunities to learn and use
the skills of research to generate new knowledge
about science and the teaching and learning of science. [p. 68]
While enrolled in the course, each participating
teacher is assigned a mentor, a member of his/her Local
Implementation Team (LIT). Weekly interactions via email, fax, or telephone between the teacher and mentor is
intended to monitor progress and help resolve any problems that may arise. Teacher participants transmit
assignments to their mentor on a weekly basis. DataStreme ECS alumni agree to act as climate resource persons for their schools. They are expected to conduct
workshops for peer teachers and administrators on electronic delivery of climatic data as a classroom resource
and to demonstrate the value of real-time climate data
across the curriculum and in different grade levels. Furthermore, DataStreme ECS alumni are encouraged to
continue their interaction with LIT members (many of
whom are professional scientists) and other DataStreme
ECS participants. The goal is for this networking to continue long after the course is completed.
•
Professional development programs for teachers of
science must be coherent and integrated. Quality
preservice and inservice programs are characterized
by clear, shared goals based on a vision of science
learning, teaching, and teacher development congruent with the National Science Education
Standards....integration and coordination of the
program components so that understanding and
ability can be built over time, reinforced continuously, and practiced in a variety of situations....options
that recognize the developmental nature of teacher
professional growth and individual and group interests, as well as the needs of teachers who have
varying degrees of experience, professional expertise, and proficiency .... collaboration among the
people involved in programs....continuous program
assessment. [p. 70]
Collaboration of teachers, science educators, and
scientists took place throughout development, pilot testing, and implementation of DataStreme ECS. The
DataStreme ECS distance-learning course was first offered on a trial basis to the course LIT leaders and
members in the Spring of 2009. After some adjustments
based on experience with the trial offering, broader implementation took place with the Fall 2009 semester.
Survey-based feedback from participating teachers, science educators, and scientists (serving as LIT members)
continues to help refine the content and structure of
DataStreme ECS.
Assessment is continuous.
DataStreme ECS participants/alumni represent all grade
levels and vary widely in scientific background and
teaching experience. Analysis of questionnaires from the
pilot test indicated a high level of satisfaction with the
DataStreme ECS experience among the participants.
DataStreme ECS is structured in such a way that components can be adapted to all grade levels and a variety of
learning environments.
Assessment in Science Education
________________________________
•
Achievement and opportunity to learn science must
be assessed. [p. 79]
Teacher participants in DataStreme ECS are gaining
practical experience in assessing the value and effectiveness of inquiry-based learning. They are being asked to
assess their own progress in learning the basics of climate
science through a constructivist process. Also, they are
asked to provide weekly reports of how they are using
DataStreme ECS and its products in their classroom.
Science Content
________________________________
Teachers participating in DataStreme ECS develop
understanding in several of the science content areas addressed by the NSES report. Through DataStreme ECS,
teachers develop expertise and confidence in each of the
content areas listed below for grades K-4, 5-8, and 9-12.
The content standard is listed in brackets along with the
NSES page reference.
Through their participation in DataStreme ECS,
teachers learn not only the basic properties of the Earth
system (i.e., composition and structure), but also the processes responsible for the dynamic behavior of the global
climate. Their understanding of the Earth system enables
them to use that knowledge to illustrate for their students
some of the basic principles of physical science (e.g.,
energy transfer), the link between science and technology
(e.g., DataStreme ECS delivery system, satellite remote
sensing), and the societal implications of science (e.g.,
land use practices, energy from fossil fuels).
A DataStreme ECS participant engages in scientific
inquiry and learns how conclusions are drawn from environmental data. This experience can only make scientific
inquiry in the classroom more realistic and exciting for
students.
•
•
•
•
As a result of activities in grades K-4, 5-8, 9-12, all
students should develop.... abilities necessary to do
scientific inquiry....understandings about scientific
inquiry. [pp. 121, 143, 173]
As a result of activities in grades K-4, all students
should develop an understanding of: properties of
earth materials, objects in the sky, changes in earth
and sky [Earth and Space Science, p. 130]; science
and technology [Science and Technology, p. 135];
changes in environments [Science in Personal and
Social Perspectives, p. 138].
As a result of activities in grades 5-8, all students
should develop an understanding of: motions and
forces, transfer of energy [Physical Science, p.
149]; structure of the earth system, earth in the solar system [Earth and Space Science, p. 158];
science and technology [Science and Technology, p.
161]; natural hazards, science and technology in
society [Science in Personal and Social Perspectives, p. 166]; nature of science [History and Nature
of Science, p. 170].
As a result of activities in grades 9-12, all students
should develop an understanding of: motions and
forces, interactions of energy and matter [Physical
Science, p. 176]; energy in the earth system, geochemical cycles, origin and evolution of the earth
system [Earth and Space Science, p. 187]; science
and technology [Science and Technology, p. 190];
environmental quality, natural and human-induced
hazards, science and technology in local, national,
and global challenges [Science in Personal and Social Perspectives, p. 193]; nature of scientific
knowledge [History and Nature of Science, p. 200].
Science Education Program
________________________________
•
All elements of the K-12 science program must be
consistent with the other National Science Education Standards and with one another and developed
within and across grade levels to meet a clearly
stated set of goals. [p. 210]
DataStreme ECS deals with subject matter and learning materials that have broad application across the
curriculum and at all grade levels. As indicated in this
report, DataStreme ECS helps prepare teachers to implement many aspects of the National Science Education
Standards in their schools and individual classroom.
•
The program of study in science for all students
should be developmentally appropriate, interesting,
and relevant to students’ lives; emphasize student
understanding through inquiry; and be connected
with other school subjects. [p. 212]
DataStreme ECS focuses on subject matter (the climate in the Earth system) that has broad and practical
appeal to students and teachers. Life experiences teach
everyone something about the climate so that climate
study is an effective vehicle to learn about science. Furthermore, the climate impacts all sectors of society and
climate sciences are involved in many of today’s major
environmental issues (e.g. exotic species, minerals exploration, climate change). In studying the climate, students
and teachers apply basic concepts and principles drawn
from other scientific disciplines including, for example,
physical science and biology.
•
The science program should be coordinated with the
mathematics program to enhance student use and
understanding of mathematics in the study of science
and to improve student understanding of mathematics. [p. 214]
DataStreme ECS provides participating teachers
(and through them their students) with the opportunity to
manipulate quantitative data in the context of real-time
environmental events.
Science Education System
________________________________
•
Responsible individuals must take the opportunity
afforded by the standards-based reform movement
to achieve the new vision of science education portrayed in the Standards. [p. 233]
DataStreme ECS encompasses so many aspects of
the National Science Education Standards that course
alumni have the opportunity to serve as leaders in their
school’s effort to implement those standards.
NATIONAL SCIENCE EDUCATION STANDARDS and DataStreme ECS
Science Teaching
Inquiry based (p. 30)
Facilitate learning
Learning environment
School science pro-
(p. 32)
(p. 43)
gram (p. 51)
Appealing focus on
On-line delivery
On-line delivery
Functions as climate
the climate in the
system
system
studies resource
Earth system
person
On-line delivery
Global environmental
Climate scientists and
Global climate studies
system
issues
science educators as
across the curriculum
resource persons
Functions as climate
National scope
studies resource
Climate science in
grades K-12
person
Professional Development for Teachers of Science
Inquiry-based (p. 59)
Science & pedagogy
Lifelong learning
Integrated and
(p. 62)
(p. 68)
coherent (p. 70)
Global climate studies
Benchmark
Local Implementation
Collaborative
in real-time
investigations with
Team (LIT) mentor
development of
pedagogical
Project
components
Constructivist
Project-based
Function as climate
approach
science
studies resource
Continual assessment
person
Many learning
Networking through
components/resources
LITs
Adaptable program
High level of
participant satisfaction
Science Content
Grades K-4 (p. 121)
Grades 5-8 (p. 143)
Grades 9-12 (p. 173)
Scientific inquiry
Scientific inquiry
Scientific inquiry
Properties of Earth materials
Motions and forces
Motions and forces
Objects in the sky
Transfer of energy
Interactions of energy and
matter
Changes in Earth and sky
Structure of the Earth system
Energy in the earth system
Science and technology
Science and technology
Geochemical cycles
Changes in environments
Natural hazards
Origin and evolution of the
Earth system
Nature of science
Science and technology
Environmental quality
Natural and human-induced
hazards
Science and technology in
local, national, and global
challenges
Nature of scientific knowledge