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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. Climate Studies: Investigations Manual 3rd Edition 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. Climate Studies: Investigations Manual 3rd Edition 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: Climate Studies: Investigations Manual 3rd Edition 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)]. Climate Studies: Investigations Manual 3rd Edition 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”. Climate Studies: Investigations Manual 3rd Edition 1A - 8 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)]. Climate Studies: Investigations Manual 3rd Edition 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. Climate Studies: Investigations Manual 3rd Edition 1B - 7 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] Climate Studies: Investigations Manual 3rd Edition 1B - 8 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. Climate Studies: Investigations Manual 3rd Edition 2B - 1 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 Climate Studies: Investigations Manual 3rd Edition 2B - 2 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. Climate Studies: Investigations Manual 3rd Edition 2B - 3 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 Climate Studies: Investigations Manual 3rd Edition 2B - 4 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 Climate Studies: Investigations Manual 3rd Edition 2B - 5 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)]. Climate Studies: Investigations Manual 3rd Edition 2B - 6 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 Climate Studies: Investigations Manual 3rd Edition 2B - 7 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. Climate Studies: Investigations Manual 3rd Edition 2B - 8 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. Climate Studies: Investigations Manual 3rd Edition 3A - 1 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 Climate Studies: Investigations Manual 3rd Edition 3A - 2 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 Climate Studies: Investigations Manual 3rd Edition 3A - 3 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). Climate Studies: Investigations Manual 3rd Edition 3A - 4 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. Climate Studies: Investigations Manual 3rd Edition 3A - 5 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. Climate Studies: Investigations Manual 3rd Edition 3A - 6 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. Climate Studies: Investigations Manual 3rd Edition 3A - 7 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. Climate Studies: Investigations Manual 3rd Edition 3A - 8 Climate Studies: Investigations Manual 3rd Edition 5A - 1 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 Climate Studies: Investigations Manual 3rd Edition 5A - 2 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. Climate Studies: Investigations Manual 3rd Edition 5A - 3 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. Climate Studies: Investigations Manual 3rd Edition 5A - 4 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 5A - 5 [(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. Climate Studies: Investigations Manual 3rd Edition 5A - 6 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 9B - 2 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] Climate Studies: Investigations Manual 3rd Edition 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)]. Climate Studies: Investigations Manual 3rd Edition 9B - 5 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. Climate Studies: Investigations Manual 3rd Edition 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 goals of (1) attracting young people to further studies in science, mathematics and technology, and (2) promoting 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