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DataStreme
Earth’s Climate System:
Climate Science for Today’s World
American Meteorological Society
DataStreme Earth’s Climate System:
Climate Science for Today’s World
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 14,000 professional
members from more than 100 countries and over 175 corporate and institutional members representing 40
countries.
The Education Program is the initiative of the American Meteorological Society to foster the teaching of
atmospheric, oceanic, hydrologic and related topics across the curriculum in grades K-12. It is a unique
partnership between scientists and teachers with the ultimate goal of attracting young people to further studies in
science, mathematics and technology via the development and dissemination of scientifically accurate,
up-to-date, and instructionally sound resource materials for teachers and students.
DataStreme Earth’s Climate System (ECS), a major component of the AMS education initiative, is a teacher
enhancement program conducted with support from the National Aeronautics and Space Administration
(NASA) and State University of New York at Brockport. DataStreme Earth’s Climate System provides teachers
with a comprehensive study of climate science using the perspective of the Earth system and current
environmental information while simultaneously considering classroom applications. It provides real
experiences demonstrating the value of computers and electronic access to time-sensitive information.
This project was supported, in part,
by the
National Aeronautics and Space Administration
Opinions expressed are those of the authors and not necessarily
those of the Administration
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. Permission is hereby granted for the reproduction, without alteration, of
materials contained in this publication for non-commercial use in schools or in other teacher enhancement
activities on the condition their source is acknowledged. This permission does not extend to delivery by
electronic means.
©2010 American Meteorological Society
45 Beacon Street. Boston, MA 02108
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Earth's Climate System
An Earth System Approach
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 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.
Welcome to DataStreme Earth’s Climate System (ECS)! You are about to be introduced to the study of Earth
system science through the investigation of climate. The statement above describes climate, why it is important,
and how it has and will impact all of our lives.
The interactions between all portions of the Earth system, especially between atmosphere and ocean, form the
major focus of climate science. Climate is pervasive on our planet; it is an ideal vehicle to study science.
Climate study uses both directly measured and remotely sensed data that are readily available via the Internet.
It’s also a great way to begin exploring the potential of the Internet as a provider of current information about
the environment.
Hands-on investigations follow that show how water can be tracked through the Earth system, how the ocean
bottom topography reflects plate tectonics, how the ocean and atmosphere interact, and how ocean circulations
are driven by wind and density variations. In each investigation, you will be shown how you can apply what
you have learned to understand and interpret ocean information delivered to your school by Internet.
The contents of this guide have been developed as part of the American Meteorological Society’s DataStreme
Earth’s Climate System course and are primarily intended for peer-training use by Climate Education Resource
Teachers. Major funding for DataStreme ECS is through the National Aeronautics and Space Administration
(NASA).
Contents:
Narrative:
Activity A:
Activity B:
Activity C:
Activity D:
Climate Science for Today’s World
Today’s Climate Science
Climate Variability and Change
Climate and Climate Variability from the Instrumental Record
The Ocean in Earth’s Climate System
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Climate Science for Today’s World
You 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.
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), pathways for transfer
of climate-sensitive materials (e.g., greenhouse gases)
and energy among Earth-bound reservoirs.
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
1
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.
Selection of an internationally agreed 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. 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.
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. The
status of the planetary system (that is, the Earthatmosphere-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 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.
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.
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
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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. 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 climateproof 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.
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. 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.
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.
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. The view of Planet
Earth in Figure 1, 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. 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]
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ATMOSPHERE
Earth’s atmosphere is a relatively thin
envelope of gases and tiny suspended particles
surrounding the planet. But the thin atmospheric skin
is essential for life and the orderly functioning of
physical, chemical and biological processes on Earth.
Nitrogen (N2) and oxygen (O2), the chief atmospheric
gases, make up a uniform 78.08% and 20.95% by
volume, respectively through most of the atmosphere.
Not counting water vapor (with its highly variable
concentration), the next most abundant gases are argon
(0.93%) and carbon dioxide (0.038%). Many other
gases occur in the atmosphere in trace concentrations,
including ozone (O3) and methane (CH4) (Table 1).
Unlike nitrogen and oxygen, the percent volume of
some of these trace gases varies with time and location.
TABLE 1
Some Gases Composing Dry Air in the Lower
Atmosphere
Gas
% by volume
78.08
Nitrogen (N2)
20.95
Oxygen (O2)
Argon (Ar)
0.93
Carbon Dioxide (CO2) 0.0388
0.00014
Methane (CH4)
0.00005
Nitrous Oxide (N2O)
0.000007
Ozone (O3)
Parts per million
780,840.0
209,460.0
9,340.0
388.0
1.4
0.5
0.07
Aerosols, minute solid and liquid particles,
suspended mainly in the lower atmosphere derive from
wind erosion of soil, ocean spray, forest fires, volcanic
eruptions, industrial chimneys, and the exhaust of
motor vehicles. Although aerosol concentrations are
relatively small, they participate in some important
processes. Aerosols are nuclei for cloud formation,
interact with incoming solar radiation and dust blown
out over the tropical Atlantic Ocean from North Africa
may affect the development of tropical cyclones
(hurricanes and tropical storms).
The significance of an atmospheric gas is not
necessarily related to its concentration.
Some
atmospheric components that are essential for life
occur in very low concentrations. For example, most
water vapor is confined to the lowest kilometer or so of
the atmosphere and is never more than about 4% by
volume even in the most humid places on Earth (e.g.,
over tropical rainforests and seas). But without water
vapor, the planet would have no water cycle, no rain or
snow, no ocean, and no fresh water. Also, without
water vapor, Earth would be much too cold for most
forms of life to exist. Water vapor is the main
greenhouse gas, one that interacts with infrared
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radiation.
Although comprising only 0.038% of the
lower atmosphere, carbon dioxide is essential for photosynthesis. Without carbon dioxide, green plants and
the food webs they support could not exist. While the
atmospheric concentration of ozone (O3) is minute, the
chemical reactions responsible for its formation (from
oxygen) and dissociation (to oxygen) in the
stratosphere (mostly at altitudes between 30 and 50
km) shield organisms on Earth’s surface from
potentially lethal levels of solar UV radiation. Carbon
dioxide and ozone are also greenhouse gases.
The atmosphere is dynamic; the atmosphere
continually circulates in response to different rates of
heating and cooling within the rotating planetary
system. Heat is conveyed from warmer locations to
colder locations, from Earth’s surface to the
atmosphere and from the tropics to higher latitudes.
The global water cycle and accompanying phase
changes of water play an important role in this
planetary-scale transport of heat energy.
HYDROSPHERE
The hydrosphere is the water component of
the climate system. Water continually cycles among
reservoirs within the climate system. The ocean, by far
the largest reservoir of water in the hydrosphere, covers
about 70.8% of the planet’s surface and has an average
depth of about 3.8 km (2.4 mi). About 96.4% of the
hydrosphere is ocean salt water. The next largest
reservoir in the hydrosphere is glacial ice (also
considered the cryosphere), most of which covers
much of Antarctica and Greenland. Ice and snow make
up 2.1% of water in the hydrosphere. Considerably
smaller quantities of water occur on the land surface
(lakes, rivers), in the subsurface (soil moisture,
groundwater), the atmosphere (water vapor, clouds,
precipitation), and biosphere (plants, animals).
The ocean and atmosphere are coupled such
that the wind drives surface ocean currents. Winddriven 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.
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 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 ocean via groundwater flow.
CRYOSPHERE
The frozen portion of the hydrosphere, the
cryosphere, encompasses massive continental (glacial)
ice sheets, much smaller ice caps and mountain
glaciers, ice in permanently frozen ground (permafrost), 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. The Greenland and Antarctic ice
sheets in places are up to 3 km (1.8 mi) thick. The
Antarctic ice sheet contains 90% of all ice on Earth.
Much smaller glaciers (tens to hundreds of meters
thick) primarily occupy the highest mountain valleys
on all continents. At present, glacial ice covers about
5
10% of the planet’s land area but at times during the
past 1.7 million years, glacial ice expanded over as
much as 30% of the land surface, primarily in the
Northern Hemisphere.
As snow accumulates, the pressure exerted by
the new snow converts underlying snow to ice. As the
ice forms, it preserves traces of the original seasonal
layering of snow and traps air bubbles. Chemical
analysis of the ice layers and air bubbles in the ice
provides clues to climatic conditions at the time the
original snow fell. Ice cores extracted from the
Greenland and Antarctic ice sheets yield information
on changes in Earth’s climate and atmospheric
composition extending as far back as hundreds of
thousands of years—to 800,000 years or more in
Antarctica.
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.
Likewise, irregularly shaped icebergs break off the
glacial ice streams of Greenland and flow out into the
North Atlantic Ocean, posing a hazard to navigation.
Most sea ice surrounding Antarctica forms
each winter through freezing of surface seawater.
During summer most of the sea ice around Antarctica
melts, whereas in the Arctic Ocean sea ice can persist
for several years before flowing out through Fram
Strait into the Greenland Sea, and eventually melting.
This “multi-year” ice loses salt content with age as
brine, trapped between ice crystals, melts downward,
so that Eskimos can harvest this older, less salty ice for
drinking water.
How long is water frozen into glaciers?
Glaciers normally grow (thicken and advance) and
shrink (thin and retreat) slowly in response to changes
in climate. Mountain glaciers respond to climate
change on time scales of a decade. Until recently,
scientists had assumed that the response time for the
Greenland and Antarctic ice sheets is measured in
millennia; however, two Greenland glaciers have
exhibited significant changes in discharge in only a few
years. Changes in ice surface elevation were detected
by sensors onboard NASA’s Ice, Cloud, and Land
Elevation Satellite (ICESat). Hence, ice sheet glaciers
may behave more like mountain glaciers, raising
questions regarding the long-term stability of polar ice
sheets and their response to global climate change.
GEOSPHERE
The geosphere is the solid portion of the
planet consisting of rocks, minerals, soil, and
sediments. Surface geological processes encompass
weathering and erosion occurring at the interface
between Earth’s crust and the other Earth subsystems.
Weathering entails the physical disintegration,
chemical decomposition, or solution of exposed rock.
Rock fragments produced by weathering become
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 fragment rock when the water
saturates tiny cracks and pore spaces. Often the water
is not as confined and fragmentation is due to stress
caused by the growth of ice lenses within the rock.
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). 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 water 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
crustal plates. The overlying crust and rigid mantle 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
periodically assembling into supercontinents and then
splitting apart. The most recent supercontinent, called
Pangaea (Greek for “all land”), broke apart about 200
6
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. 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. 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.
BIOSPHERE
All living plants and animals on Earth are
components of the biosphere. 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.
Organisms on land or in the atmosphere live close to
Earth’s surface. However, marine organisms occur
throughout the ocean depths and even inhabit rock
fractures, volcanic 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 fractured rocks on and
below the ocean floor may vastly exceed the mass of
organisms living on or above it.
Photosynthesis and cellular respiration are
essential for life near the surface of the Earth, and
exemplify how the biosphere interacts with the other
subsystems of the climate system. Photosynthesis is
the process whereby green plants convert light energy
from the Sun, carbon dioxide from the atmosphere, and
water to sugars and oxygen (O2). The sugars, which
contain a relatively large amount of energy and
oxygen, are essential for cellular respiration. Through
cellular respiration, an organism processes food and
liberates energy for maintenance, growth, and reproduction, also releasing carbon dioxide, water, and heat
energy to the environment. With few exceptions,
sunlight is the originating source of energy for most organisms living on land and in the ocean’s surface
waters.
Dependency between organisms on one
another (e.g., as a source of food) and on their physical
and chemical environment (e.g., for water, oxygen,
carbon dioxide, and habitat) is embodied in the concept
of ecosystem. Ecosystems consist of plants and
animals that interact with one another, together with
the physical conditions and chemical substances in a
specific geographical area. An ecosystem is home to
producers (plants) which take nutrients to produce
foods, consumers (animals) which consume the food to
grow, and decomposers (bacteria, fungi) which return
nutrients to the environment.
Feeding relationships among organisms,
called a food chain, can be quite simple or more
complex as in a food web. In a food chain, each stage,
a trophic (or feeding) level transfers only about 10% of
the energy available to the next higher level, i.e.
producers to consumers to decomposers. Because
mass transfers are more easily measured than energy,
biomass, the total weight or mass of organisms, is
generally tracked through food chains or webs.
Climate is the principal ecological control,
largely governing the location and species composition
of natural ecosystems such as deserts, rain forests, and
tundra. 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 an 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
long-established
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.
Subsystem Interactions: Biogeochemical
Cycles
Biogeochemical cycles are the pathways along which
7
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).
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. This cycling will
include gains to or losses from a reservoir through
chemical reactions within the reservoir. 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.
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 respiration. In addition to the
uptake of CO2 via photosynthesis, marine organisms
also use carbon for calcium carbonate (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
Subsequently, tectonic
dolostone (CaMg(CO3)2).
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 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
8
(detritus) accumulated on the ocean bottom and in lowlying 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
operating 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.
Investigation A:
TODAY’S 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.
After completing this investigation, you should be able to:



Describe Earth’s climate system and its interacting components.
Describe and compare the complementary empirical and dynamic definitions of climate.
Explain the AMS Climate Paradigm.
An Earth System Approach
Earth’s Climate System (ECS) employs an Earth system perspective. A view of the Earth
system as seen from space is presented in Figure 1 of the Narrative. Examine the figure for
evidence of the major components of the Earth system — atmosphere, ocean, biosphere,
cryosphere (including ice sheets, sea ice, glaciers, and seasonal snow cover), and land
surface. These components, or sub-systems, interact and determine Earth’s climate.
1. With our feet almost always firmly on the solid Earth, we live primarily in the
atmosphere. It delivers our essential oxygen and provides other nutrients (e.g., carbon,
nitrogen) to support living plants and organisms. The thinness of the atmospheric
subsystem is evident primarily in Figure 1 [(over the continents)(in the middle of the
figure)(along Earth’s visible circumference)].
2. The ocean water surfaces are displayed in the image in hues of blue and green because
water selectively scatters those colors of the visible solar spectrum back toward space.
Even in this Figure 1 perspective where portions of four or perhaps five of the seven
continents are seen, Earth's surface area is clearly [(more land than ocean)(about the
same land as ocean)(more ocean than land)].
3. In this Figure 1 perspective, the North Pole is approximately in the center of the broad
expanse of uniform light gray Arctic Ocean sea ice which is seen in the image above the
bright-white ice sheet covered [(Canada’s Baffin Island)(Greenland)(Iceland)]. This,
the world’s largest island, is covered by ice up to 3 km (1.8 miles) thick which if melted
would increase the global sea level by 7.2 m (23.6 ft). Significant melting of this ice
sheet is just one likely outcome of global warming, demonstrating why it is essential that
we better understand the scientific workings of Earth’s climate system and the possible
consequences of climate change.
A-1
4. In Figure 1 the biosphere is evident primarily by way of the [(whitish)(greenish)
(brownish)] hues of chlorophyll as seen in the Amazon Basin as compared to
surrounding land and in near-shore ocean waters as along the southeastern U.S. coasts.
Weather, Climate and Climate Change
In Earth's Climate System, we will examine the unique combinations of conditions of the
physical and biological environment that arise from the interplay of Earth’s subsystems in
response to external influences (called forcings).
Fundamental to understanding weather, climate and climate change is the recognition that the
Earth system is a complex energy flow system. The observable impacts of the energy flows
(and associated mass flows) are embodied in the descriptions of weather and climate.
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 as it is based on the descriptions of weather observations in terms of the average
and variability of quantities such as temperature, precipitation and wind over periods of
several decades (typically the three most recent decades). Climate thusly defined can be
thought of as the quantified description of the weather involving averages of appropriate
components (e.g., temperature, precipitation), together with the statistical variations of those
components.
Climate can also be delineated 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, 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 being primarily an atmospheric
phenomenon, climate exhibits persistence arising from it being essentially an Earth system
creation.
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, 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.
5. Local climatic data, including records of observed temperature, precipitation, humidity,
and wind, are examples of [(dynamically)(empirically)] derived information.
A-2
6. 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.
A scientific model is an approximate representation or simulation of a real system.
Computer-based mathematical climate models can be either empirical or dynamic. Empirical
climate models, based as they are on data sets of actual meteorological observations, are most
appropriately used to predict climate variability. Dynamic climate models, based as they are
on interacting forcing mechanisms, are best used to predict climate change.
7. Computer-based climate models that attempt to determine the impact of increasing
concentrations of atmospheric carbon dioxide on future global temperatures produce
[(dynamically)(empirically)] derived information.
8. Computer climate models relying on large databases describing past weather that attempt
to forecast the probability of record low winter temperatures or the frequency of drought
produce [(dynamically)(empirically)] derived information.
Figure A1 schematically depicts the components, or sub-systems, of Earth’s climate system
(atmosphere, ocean, terrestrial and marine biospheres, cryosphere, and land surface). These
major components interact with each other through flows of energy in various forms, through
Figure A1. Schematic view of the components of the climate system, their processes and
interactions. [IPCC AR4 WG1 faq-1-2-fig-1]
A-3
exchanges of water, through flows of greenhouse gases (e.g., carbon dioxide, methane), and
through the cycling of nutrients. Solar energy is the ultimate source of the driving force for
the motion of the atmosphere and ocean, the flows of heat and water, and of biological
activity.
9. The arrows in the figure identify the processes and interactions with and between the
major Earth climate system components. The double-headed arrows show that
[(few)(about half)(almost all)] of the processes and interactions between climate system
components (e.g., precipitation-evaporation, land-atmosphere) involve bi-directional
(upward/downward) flows.
10. Of all the processes shown in Figure 2, most are interactions within the Earth system. A
process that would be an external forcing of the climate system is [(changes in the
cryosphere)(changes in solar inputs)(clouds)].
11. Six of the displayed interactions depicted in Figure 2 are specifically labeled “Changes in
…”. While changes in the atmosphere (composition) is the one that most impacts global
climate due to human activity, the one that most directly states human activity which
alters the environment is the one concerning the [(ocean)(land surface)(hydrological
cycle)(cryosphere)].
The Earth's Climate System Paradigm:
Utilizing a planetary-scale Earth system perspective, ECS explores Earth’s climate system.
In pursuing this approach, ECS is guided and unified by a special climate paradigm that is
given in the Preface, page ii. Refer to that Paradigm for these questions.
12. It is implied in the AMS Climate Paradigm that components of the Earth system (e.g.,
atmosphere, hydrosphere, cryosphere, geosphere, and biosphere) interact in a(n)
[(random)(orderly)] way as described by natural laws.
13. This interaction of the Earth system components through natural laws would imply a(n)
[(dynamic)(empirical)] perspective for climate studies.
14. The ocean as an Earth system component and player in atmosphere/ocean energy and
mass distributions suggest it is a [(major)(minor)] part of biogeochemical cycles (e.g.,
water cycle, carbon cycle) operating in the Earth system.
15. According to the AMS Climate Paradigm, our understanding of the climate system is
incomplete. However, 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)].
In summary, Earth’s Climate System investigates climate science through complementary
empirical and dynamic approaches as guided by the AMS Climate Paradigm.
A-4
Investigation B:
CLIMATE VARIABILITY AND CHANGE
Driving Questions: What is climate change? Is there short-term evidence that human
activity can modify climate? How can we objectively determine
modification of climate?
Introduction: Earth’s climate changes when the amount of energy stored by the climate system
is varied. The 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 short-term variations in the climate or of persistent change in the climate system. When are
we observing statistical fluctuations of climate measures and when 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
deviations, 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
measures persisting over several decades or longer. Climate change occurs ultimately due to
alteration of the global energy balance between incoming solar energy and outgoing heat
from Earth. 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 forcing the climate to change 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 nearly universally as due mostly to
increasing atmospheric carbon dioxide through the burning of fossil fuels. Among other
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).
B-1
Educational Outcome: 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.
After completing this investigation, you should be able to:


Describe one instance of climate change likely to be caused by human activity.
Explain how stopping particular human activity may have resulted in a return of the
climate to its original state.
Investigation:
The scientific and 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 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 Grand Island, NE Local Climatological Data (LCD), Annual Summary for 2008, a
publication of climatic data for selected stations by the National Climatic Data Center, gives
the mean daily temperature for February 2008 as 27.7 °F. In the companion Normals,
Means, and Extremes table for Grand Island it shows that the normal average daily
temperature (same as normal dry bulb) for February is 28.2°F.
1. The difference in Grand Island’s mean daily temperature for February 2008 and the
February normal value reveals a [(0.5)(9.3)(21.4)] F° lower-than-normal temperature.
The difference is a measure of and example of climate variability.
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 and that used by the International
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. The context in which the term appears will
usually inform the reader of the definition employed.)
2. Determination of whether or not climate change has occurred [(does)(does not)] require
comparison of climate variability about a mean climate state determined from empirically
acquired climatic data for the same locality.
B-2
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 (Figure B1). 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.
Figure B1. NASA MODIS image of contrails over southeastern U.S. [NASA]
http://earthobservatory.nasa.gov/images/imagerecords/4000/4435/contrails
_southeast_lrg.gif
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. Figure B2, from an International Panel on Climate Change special report,
Aviation and the Global Atmosphere (IPCC, 1999) shows the contrail cover in percentages
based on the 1992 aviation fleet and based on certain other assumptions.
B-3
Figure B2. Persistent contrail coverage (in % area cover) for the globe for the 1992 aviation
fleet. The global mean cover is 0.1%. [From Sausen et al., 1998.]
3. According to the special IPCC report, the global mean contrail cover in 1992 was
estimated to be 0.1%. Figure B2 color coding shows that the greatest contrail cover
reached levels approaching at least 1.0% in some locations. Note that the southeastern
U.S. as seen in Figure B1 is a region of elevated persistent contrail coverage. Figure B2
shows that the largest contiguous area of elevated contrail cover 2.0% and higher is
located over [(Europe)(East Asia)(North America)]. Note the lanes over the ocean
where air traffic is obviously heavy.
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 are likely to 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 by 2%-5% in the decades ahead. Figure B3 depicts persistent contrail coverage
(in % area cover) as projected for the Year 2050. The prediction is based on meteorological
data and assumptions including fuel emission databases.
B-4
Figure B3. Persistent contrail coverage (in % area cover). Global mean cover is 0.5%.
(From Gierens et al., 1998.)
4. Compare Figures B2 and B3. Captions to the two figures indicate that the global mean
cover of persistent contrail coverage is expected to increase from 0.1% in 1992 to
[(0.1%)(0.2%)(0.5%)] in 2050.
5. During the same time period between 1992 and 2050, the areas of 3.0% or more coverage
will [(increase)(remain the same)(decrease)]. Note that the areas of highest persistent
contrail coverage (except for the heavily traveled air lanes) are over areas of great human
population concentrations. The areas of highest potential climate impacts are less than
global in scale, but they are in locations likely to impact huge numbers of people.
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 missiles to destroy buildings, 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.
B-5
U.S. skies remained essentially clear of aircraft for a day or more. In general, the grounding
remained in effect until 13 September or later. 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. Considerable amounts of the absorbed
radiation are 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.
6. Prof. Travis’s study of the record of observed surface air temperatures across the country
was essentially a(n) [(dynamically)(empirically)] based investigation.
7. Because of the non-uniform spatial coverage of contrails as displayed in Figure B2, any
climate change brought on by the occurrence of contrails might best be described as
affecting a [(local)(regional)(global)] 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 recent
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 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 favor unusually large daily
temperature ranges.
B-6
In conclusion, 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 gradual steady increase in contrails and contrail-related cirrus cloud cover over
the past 50 years or so has been documented. However, the net impact on daily temperature
ranges at Earth’s surface is not conclusive. 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 condition.
B-7
Investigation C:
CLIMATE AND CLIMATE VARIABILITY FROM THE
INSTRUMENTAL RECORD
Driving Questions: What can we determine from the instrumental record regarding the
variability of climate? When might that variability infer a change
in climate?
Educational Outcomes: Understanding climate and its variability are the first steps in
making sense of what factors determine the mean state of the climate system, how it may
have changed, and how it might change in the future. This course attempts to cover those
key concepts of the boundary conditions that affect Earth's climate state and how the system
varies within the limitations imposed by those constraints. We use the record of instrumental
observations from the reliable length of readings to define that climate state and to identify
its variability. From statistical analysis of the record, we then try to determine if and when a
change has occurred or can be expected to occur in that climate state.
After completing this investigation, you should be able to:



Describe where climate data may be obtained and displayed.
Show ways the climate record may be analyzed.
Explain how the climate analysis provides an understanding of climate variability and
could lead to objective evidence of climate change (past and present).
In this investigation, we will use temperature records to demonstrate ways in which climatic
data acquired by use of reliable instrumentation are employed to examine climate and its
variability. We will assess some specific temperature records for the period from 1895 to the
present in the climatological division of Nebraska that includes Grand Island, whose local
climatic data were referred to in Investigation B.
The temperature data we will analyze are monthly averages from the several sites within
climatological division 5 ("central") of Nebraska. A climatological division is a region of a
state considered to be homogeneous climatologically and containing a reasonable number of
observing sites. Here we will deal only with the July temperature averages; each value
thus being the average of 31 daily averages from approximately ten stations. The data are
from NOAA's National Climatic Data Center. These data thus represent the average
commonly warmest month's temperature of the area including and surrounding Grand Island,
Nebraska for the reliable length of temperature readings there.
In statistics, there are several terms for the most representative or middle value of a series of
data (including mean, median, and mode). Average, a sometimes vague term, is commonly
used to denote the middle value of a set of data determined by dividing the sum of the values
by the number of values used in the summation. This definition of average is synonymous
with the term mean, which statisticians prefer using to precisely define a middle value so
calculated. Finally, there is the term “normal” used in climatology. The climatological
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standard normal is the average (mean) of the 30 values of the variable within the most recent
three decadal climate period, currently 1971-2000. Here we are using the average (mean)
temperature for the month of July for each year. That average itself was the average of the
daily average temperatures for the 31 days of each July. And each daily average was the
average of that day's high and low temperatures.
Figure C1 is the time series graph of July average temperature in degrees Fahrenheit from
1895 to 2008 from NOAA's National Climatic Data Center. The average July temperature of
each year is shown by a small green square plotted at the mid-point of that year with the
years connected by line segments. The series of red squares making a horizontal line is the
average (mean) of these July averages.
Figure C1. Nebraska Central climatological division average July temperatures from 1895 to
2008. [NOAA/NCDC]
1. The average of all the July temperatures, denoted by the line of plotted red squares, is
about [(74.5)(75.1)(77.2)] F.
2. The Local Climatic Data, Annual Summary publication for Grand Island, Nebraska
(mentioned in Investigation B) gave the average July temperature for Grand Island in
2005 as 77.4 F. From Figure C1, the 2005 central climatological division which
contains Grand Island had an average July temperature that was [(less than)(equal to)
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(greater than)] the Grand Island value. The more urban nature of Grand Island
compared to the rural area's average probably accounts for this result.
3. The departure of the individual years from the average is the variability. The maximum
July average temperature in this series is about 83.6 F. This occurred in 1934. The
minimum July average temperature was 68.1 F which occurred in 1992. The range is
defined as the difference of the maximum and minimum values, and is one simple
measure of the variability of data. For the average July temperatures of this period, the
range was [(0.7)(8.4)(15.5)(29.3)] F.
4. Another issue in a long series of data such as this is the nature of these variations in the
data. For example, are there clear cycles of variation? If the values varied in a totally
random way, one would expect swings from above to below average and vice versa
occurring every year or at least every couple of years. One would not expect consistent
runs of above or below average values and certainly not much above or below for
extended periods. Using this general context, consider the periods 1902 to 1911, 1929 to
1943, and 1988 to 1997. Do these consecutive-year periods seem to imply total
randomness in year-to-year variability? [(Yes)(No)]
A climate system comprises many interacting processes, some of which serve to maintain
certain departures (positive feedbacks) and some to dampen those departures (negative
feedbacks.) Evidence exists in the Central Nebraska July temperature for both types of
behavior.
The traditionally accepted climate period of the most recent three decades (30 years) of
record for climatic values would dictate 1971-2000 as the current climatic normal period.
Draw vertical lines on your graph at 1971 and at 2000 to display this span of years. Using
the July average temperatures from these years, the following statistics were derived:
mean: 74.2 F
maximum: 79.2 F
minimum: 68.1 F
5. The 1971-2000 July average temperature is [(less than)(equal to)(greater than)] the
average of all July temperatures for 1895-2008.
6. The range of July temperatures for 1971-2000 shown in is 11.1 F. The mean and range
for the 1971-2000 period [(are)(are not)] equal to those for the 1895-2008 period.
In fact, one could compute the mean for each of the climatic normal periods within the entire
length of this temperature record. Those mean values are given below:
1901-1930
1911-1940
1921-1950
1931-1960
74.6 F
76.6 F
76.4 F
76.6 F
1941-1970
1951-1980
1961-1990
1971-2000
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75.2 F
75.2 F
74.9 F
74.2 F
A major concern facing humankind at present is the potential for global warming. This
concern comes from the recent worldwide examination of surface temperatures. We can
consider these issues from our brief look at the localized summer temperatures of central
Nebraska as a data "game". (By no means should this be considered a rigorous climate
investigation but only a very limited example of using climate data to answer possible
questions.)
7. Let us take "climate change" for our purpose here to imply simply a change of the mean
temperature from one climatic normal period to another. Compare the mean of the most
recent period, 1971-2000, to those of the preceding periods listed above. The 1971-2000
mean July temperature is [(less than any)(greater than any)] of the prior climatic periods
listed.
8. If merely a change of mean value is considered a different climate regime, has there been
a "climate change" in this case? [(Yes)(No)]
9. Next, consider the magnitude of the difference from the others in the group and also
recall the variability displayed in the graph of the total group of temperature values.
Given the small difference of the 1971-2000 mean from those others and the overall
nature and size of departures over the entire period of record (variance), could one
conclusively be sure real change had occurred? [(Yes)(No)]
10. If we are concerned with "global warming", compare the mean for the 1971-2000 period
to those of the other periods listed. The 1971-2000 period mean July temperature is
[(the lowest value)(only lower than one or two others)(in the middle of the values)
(higher than some others)(the highest value)].
One caution on these results, while there may be global trends, climate patterns are nonuniform geographically on the regional and local levels. Thus, while some areas may be
clearly warming, others may be cooling, with only the overall average showing warmer
values.
Summary: A number of ways in which recorded temperature values can be analyzed has
been shown. Although limited to July data in one climatological division, they are intended
as examples of how empirically acquired climatic data can be examined to determine climate
variability, which in turn can lead to objective evidence of climate change in the past and
present.
However, predicting climate change in the future requires a dynamic approach. As
mentioned in Investigation A, while the empirical approach allows us to construct
descriptions of climate, the dynamic approach is what enables us to seek explanations for
climate. Explanations lead to predictions, including prognostications of change. Considering
Earth’s climate system dynamically as a physical system makes it possible to leap-frog into
the future via computer models to make potentially useful climate change predictions.
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The USGCRP Global Climate Change Impacts in the United States report presents climatechange predictions on the regional scale. As an example, the report shows in Figure C2 that
climate models predict the Nebraska Central climatological division’s summer temperatures
are projected to rise 6 Fº or more compared to a 1960s and 1970s baseline.
Great Plains Projected
Summer Temperature Change by 2080-2099
Figure C2. Projected summer temperature change in the Great Plains [USGCRP].
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Investigation D:
THE OCEAN IN EARTH'S CLIMATE SYSTEM
Driving Questions: How important is the ocean to the climate system and climate
change? How are oceanic conditions changing?
Educational Outcomes: Earth's Climate System, which has been the subject of this
course, encompasses the “spheres” of the geosphere, atmosphere, hydrosphere (including the
ocean), cryosphere and biosphere along with their interactions and the variability and
changes within and because of the boundary conditions. Traditional climate studies have
often been restricted to the conditions at Earth's surface primarily due to the workings of the
atmosphere. We are culminating our investigations of Earth’s climate system by focusing on
the ocean, the system’s major component in terms of mass and energy.
After completing this investigation, you should be able to:



Explain why the ocean is the dominant energy and mass reservoir and influential
component of Earth's climate system.
Describe what influences the ocean has on and receives from, the rest of the climate
system.
Explain what changes are occurring in the ocean and what the consequences may be for
Earth’s climate system.
While we live on the land and interact most with the atmosphere, the major component of
Earth's climate system in terms of mass and energy is the ocean. The ocean covers about
71% of Earth's surface and makes up 99.8% of the mass of the fluid portions of Earth's
system (air and water). The high specific heat of water combined with the size of the ocean
reservoir gives the ocean exceptional capacity to store and transport heat. Therefore, just
from the mass and energy characteristics, the variability of the fluid portions of the planet
implies that the ocean merits major consideration when seeking understandings of Earth’s
climate system and its changes.
Change in Heat Content of Climate System Reservoirs: Figure D1 shows the
estimated heat energy content changes of various parts of the climate system for two periods:
1961-2003 (blue bars) and 1993-2003 (red bars). All of these values are for increases in the
heat storage of those portions of the climate system during the respective time periods. The
heat units are in 1022 J. [Note: (1 joule (J) = 0.239 calorie]
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Figure D1. Energy content change of portions of the climate system, from 1961-2003 (blue)
and from 1993-2003 (red). (IPCC)
1. For all of the energy content changes shown, the values varied considerably in
magnitudes. However, the estimated values were all positive. This means that from
1961 to 2003 the positive energy change implied that these parts of the climate system
[(all cooled)(some cooled and some warmed)(all warmed)].
2. The total change in the energy content of the components of Earth’s climate system
shown in Figure D1 from 1961 to 2003 was [(14.2)(15.9)(24.8)] x 1022 J.
3. Figure D1 indicates that in the 1993-2003 time period a total of 8.9 x1022 J were added to
Earth’s climate system’s heat content. Therefore, the climate system’s heat content must
have increased [(7.0)(8.11)(15.0)] x 1022 J during the earlier time period from 1961 to
1993.
4. Comparison of the 1961-1993 total change with the 1993-2003 total change infers that
the annual rate at which heat content was being added to Earth’s climate system was
generally [(decreasing)(steady)(increasing)] from year to year.
5. Compare the numbers for the energy content changes in the continents and the
atmosphere over the period 1993-2003 (red bars). For these two portions of the climate
system over this latter period, the energy content change(s) of [(continents were much
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)(continents and atmosphere were about equal)(the atmosphere was much
greater)].
6. Combining the values for the ice components of the system (glaciers, ice sheets and sea
ice) provides a total energy content change of 0.45 x 1022 J during the 1961-2003 time
period. Compared to the energy content change for the continents and atmosphere during
the same time period, the total ice energy content change was nearly equal to the change
within the [(atmosphere)(continents)] component.
7. Compared with the energy content change for Oceans for either period, the changes of all
the other portions of the climate system combined were [(much smaller)
(about the same)(much greater)].
8. Using the value for the ocean change over the 1993-2003 period compared to the total
change for the same 1993-2003 time period (red bars), the ocean accounted for about
[(10%)(25%)(50%)(75%)(90%)] of the total energy content increase in the system. This
demonstrates the prominent role the ocean must play in determining climate and climate
change.
Global Warming Impacts on the Ocean: The IPCC AR4, Climate Change 2007:
Physical Science Basis, Technical Summary, p. 47, states, “Warming is widespread over the
upper 700 m of the global ocean.” Further, “The world ocean has warmed since 1955,
accounting over this period for more than 80% of the changes in the energy content of the
Earth's climate system.” This ocean warming has several critical impacts on the climate
system.
9. The temperature change of ocean water leads to changes in evaporation and density
change. The evaporation from the ocean drives the global water cycle. Warmer water
has more energy available for evaporation. In locations where precipitation is less than
evaporation, we would expect that excess evaporation would lead to surface ocean waters
that become [(less)(more)] saline as the salts are left behind in the evaporation process.
“There is now widespread evidence for changes in ocean salinity at gyre and basin scales in
the past half century with the near-surface waters in the more evaporative regions increasing
in salinity in almost all ocean basins. These changes in salinity imply changes in the
hydrological cycle over the oceans.” (IPCC AR4, Physical Science Basis, Technical
Summary, p.48)
10. As seawater warms, it becomes less dense. Less dense water means the same mass of
water would occupy a greater volume. The result of a warming ocean would be
[(rising)(lowering)] sea level.
“The global average rate of sea level rise measured by TOPEX/Poseidon satellite altimetry
during 1993 to 2003 is 3.1 ± 0.7 mm yr–1.” (IPCC AR4, Physical Science Basis, Technical
Summary, p.49
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11. Another crucial gas dissolved in the ocean is oxygen. Dissolved oxygen is essential to
the oceanic biosphere. With a warmer ocean, [(more)(less)] O2 would be dissolved in the
water.
In fact, the IPCC states, “The oxygen concentration of the ventilated thermocline (about 100
to 1000 m) decreased in most ocean basins between 1970 and 1995. These changes may
reflect a reduced rate of ventilation linked to upper-level warming and/or changes in
biological activity.” (IPCC AR4, Physical Science Basis, Technical Summary, p.48)
Although there is no known evidence at present of its occurrence, one fear is that the warmer,
less dense water may resist sinking in the North Atlantic Ocean basin. It is that sinking that
drives the global meridional overturning circulation, a massive inter-basin heat engine for the
ocean system. And, warmer ocean surface waters in tropical regions could lead to greater
tropical cyclone activity through an increase in the number of storms, by storms becoming
more intense, or both.
Ocean Acidification: Associated with the changes already mentioned is the impact of
increased carbon dioxide in the atmosphere and ocean.
Of the carbon dioxide that is emitted into the atmosphere, about 56% is taken up by
dissolving in the ocean. The ocean is normally slightly alkaline. The CO2 that dissolves in
ocean waters forms a weak acid solution that increases the acidity of the waters, causing pH
values to decrease (the lower the pH, the higher the acidity). One consequence is that the
calcium carbonate shells or structures of many ocean creatures become more soluble in more
acidic waters. Ocean life will have difficulty living in a more acidic ocean. “The uptake of
anthropogenic carbon since 1750 has led to the ocean becoming more acidic, with an average
decrease in surface pH of 0.1 units.” (IPCC AR4, Physical Science Basis, Technical
Summary, p.48)
12. As seen in this investigation, we [(can)(cannot)] ignore the role of the ocean if we want
to more completely understand Earth’s climate system.
13. The ocean plays a [(minor)(major)] role in the climate system through its cycling of mass
and energy.
Summary: We now go back to reconsider the Earth's Climate System paradigm, which
was addressed in the Preface, page ii of this guidebook. This statement provided us a guiding
definition of climate, the climate system and the ways humans interact with and affect that
system of which they are a part. “Climate arises primarily from the complex redistribution of
energy and mass by Earth’s coupled atmosphere/ocean system.” Many of the investigations
in this course examined the boundary conditions that derived from the physical processes at
work on and in the climate system. We also looked at the mean state of the system and its
variability within those boundaries.
Your knowledge of Earth’s climate system will be enhanced by considering both its
empirical and dynamic perspectives. The more we know about the environment in which we
live, the more informed we will be to work toward making it a better place for everyone.
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