At a time when responding to our changing climate is one of the nation’s

most complex endeavors, reports from the National Academies provide

thoughtful analysis and helpful direction to policymakers and stakeholders.

These reports are produced by committees organized by the Board on

Atmospheric Sciences and Climate, its Climate Research Committee, and

numerous other entities within the National Academies. With support from

sponsors, the National Academies will continue in its science advisory role

to the agencies working on understanding changing climate, documenting its

impacts, and developing effective response strategies.

U N D E R S T A N D I N G A N D R E S P O N D I N G T O

CLIMATECHANGE

H i g h l i g h t s o f

N a t i o n a l A c a d e m i e s R e p o r t s

National Academy of SciencesNational Academy of Engineering

Institute of MedicineNational Research Council

U N D E R S T A N D I N G A N D R E S P O N D I N G T O

CLIMATECHANGE

A G R O W I N G B O D YO F E V I D E N C E

indicates that the Earth’s atmosphere is warming. Records show that surface temperatures have risenabout 1.4oF (0.7oC) since the early twentieth century, and that about 0.9oF (0.5oC) of this increasehas occurred since 1978. Observed changes in oceans, ecosystems, and ice cover are consistentwith this warming trend.

The fact is that Earth’s climate is always changing. A key question is how much of the observedwarming is due to human activities and how much is due to natural variability in the climate. In the judgment of most climate scientists, Earth’s warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmos-phere (see Figure 1). Greenhouse gases have increased significantly since the Industrial Revolution,mostly from the burning of fossil fuels for energy, industrial processes, and transportation.Greenhouse gases are at their highest levels in at least 400,000 years and continue to rise.

Global warming could bring good news for some parts of the world, such as longer growing seasons and milder winters. Unfortunately, it could bring bad news for a much higher percentage ofthe world’s people. Those in coastal communities, many in developing nations, will likely experienceincreased flooding due to sea-level rise and more severe storms and surges. In the Arctic regions,where temperatures have increased almost twice as much as the global average, the landscape andecosystems are rapidly changing.

Although the potential effects of climate change are widely acknowledged, there is still legitimate debate regarding how much, how fast, and where these effects will take place. Climate sci-ence is just beginning to project how climate change might affect regional weather. Predicting climatechange impacts also requires predicting society’s future actions, particularly in the areas of populationgrowth, economic growth, and energy use.

GLOBAL WARMING OR CLIMATE CHANGE? The phrase "climate change" is growing in preferred use to "global warming" because it helps convey that there are changes in addition to rising temperatures.

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Extreme weather events over the pastseveral years—the hurricane season of 2004, hurricanes Katrina, Rita, andWilma in 2005, a sustained drought inthe U.S. West, the first ever hurricane inthe South Atlantic in 2004, the 2003heat wave in Europe—have raised aquestion: Are these events possibly associ-ated with climate change? It is very diffi-cult to point to any one single event andascribe its cause to climate change.However, the collection of such eventsmay indicate a contribution from climatechange, and the likelihood of extremeevents could increase in the future.

This brochure highlights importantthemes and recommendations fromNational Academies’ reports on climatechange. These reports are the products

of the National Academies’ studyprocess, which brings together leadingscientists, engineers, public health offi-cials, and other experts to address spe-cific scientific and technical questions.On climate change, such reports haveassessed consensus findings on the sci-ence, identified new avenues of inquiryand critical needs in the observing andcomputational research infrastructure,and explored opportunities to use scien-tific knowledge to more effectivelyrespond to climate change.

How climate will change in the future isinherently uncertain, but far from unknown.If scientific uncertainty about climate changeis used to delay action, the risks and costsof adverse effects of climate change couldincrease significantly.

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Figure 1. The greenhouseeffect is a natural phenomenon that is essential to keeping theEarth’s surface warm.Without it, there would notbe life as we know it. Like agreenhouse window, greenhouse gases allowsunlight to enter and then

prevent heat from leavingthe atmosphere. Watervapor (H2O) is the mostimportant greenhouse gas,followed by carbon dioxide(CO2), methane (CH4),nitrous oxide (N2O), halocarbons, and ozone(O3). However, much higherconcentrations of green-house gases than naturallyoccur—mostly from burning fossil fuels—aretrapping excess heat in theatmosphere and are warming Earth’s surfacefaster than at any time inrecorded history. Source:Okanagan UniversityCollege, Canada; University of Oxford; U.S.Environmental ProtectionAgency; United NationsEnvironment Programme(UNEP) and WorldMeteorologicalOrganization (WMO).

Figure 2. Global annual-mean surface air temperature has increased by 1.4º F (0.7ºC) since the early 20th century, with about0.9ºF (0.5ºC) of the increaseoccurring since 1978. Figure courtesy of Goddard Institute forSpace Studies.

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ABOUT THE SCIENCE

Changes observed over the last

several decades are likely mostly

due to human activities.

—National Research Council, 2001

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1880 1900 1920 1940 1960 1980 2000

The Earth is warming.Climate is conventionally defined as thelong-term average of weather condi-tions, such as temperature, cloudiness,and precipitation; trends in these condi-tions for decades or longer are a primarymeasure of climate change. The moststriking evidence of a global warmingtrend is closely scrutinized data thatshow a relatively rapid and widespreadincrease in temperature during the pastcentury (see Figure 2).

The rising temperatures observed since1978 are particularly noteworthy because

the rate of increase is so high andbecause, during the same period, theenergy reaching the Earth from the Sunhad been measured precisely enough toconclude that Earth's warming was not due to changes in the Sun. Scientistsfind clear evidence of this warming trendeven after removing data from urbanareas where an urban heat-island effectcould influence temperature readings.Furthermore, the data are consistent withother evidence of warming, such asincreases in ocean temperatures, shrink-ing mountain glaciers, and decreasingpolar ice cover.

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ual G

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One issue that had emerged in the climate change debate is whether temperature measurements are reliable.Temperature readings of the loweratmosphere taken with satellites appearedto show less warming than thermometerreadings taken near the surface of theEarth. Some skeptical scientists interpret-ed this discrepancy to mean that globalwarming is not occurring and that thesurface data are flawed.

A report released in 2000, ReconcilingObservations of Global TemperatureChange, examined this conflict in detailand concluded that the warming trend in global-average surface temperatureobservations during the past 20 years isundoubtedly real. The report spurredother groups to examine the discrepan-cy; they found that trends in satellite datawere affected by instrument calibrationand difficulties in interpreting tempera-ture readings through the vertical extentof the atmosphere. Recent satellite andsurface data are in better agreement,largely resolving the dispute.

Humans have had an impact onclimate.In May 2001, the White House asked theNational Academy of Sciences to assessour current understanding of climatechange by answering several key ques-tions related to the causes of climatechange, projections of future change,and critical research directions toimprove understanding of climatechange. Climate Change Science: AnAnalysis of Some Key Questionsresponded directly to those questions.The report’s often-cited conclusion is that“changes observed over the last severaldecades are likely mostly due to humanactivities” with some contribution fromnatural variability.

How do we know this to be true? Therole of atmospheric carbon dioxide inwarming the Earth’s surface was firstdemonstrated by Swedish scientistSvante Arrhenius more than 100 yearsago. Scientific data have since estab-lished that, for hundreds of thousands ofyears, changes in temperature have

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Figure 3. As recorded in ice coresfrom Vostok, Antarctica, the temperature near the South Pole has varied by more than 20º F duringthe past 350,000 years, and the temperature has corresponded closelywith CO2 concentrations. There havebeen peaks of warmth approximatelyeach 100,000 years. The rise and fallof temperatures constitute the iceage/interglacial cycle. Image courtesyof the Marian Koshland ScienceMuseum of the National Academy of Sciences.

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closely tracked with atmospheric carbondioxide (CO2) concentrations (see Figure

3). The burning of fossil fuels (oil, naturalgas, and coal) releases carbon dioxide tothe atmosphere. About 80% of the energyused in the United States is derived fromfossil fuels. The recent rapid rise in bothsurface temperature and CO2 is one ofthe indications that humans are respon-sible for some of this unusual warmth. In addition, model predictions of temper-ature change have been shown to closely match observed temperaturechanges when data from both naturaland human-induced causes are usedtogether (see Figure 4).

There are several factors that contributeto Earth’s warming and cooling. To compare the contributions of variousfactors, scientists have devised the con-

Figure 5. Various climate drivers, or radiative forcings,act to either warm or cool the Earth. Positive forcings,such as those due to greenhouse gases, tend to warm the Earth, while negative forcings, such as aerosols from industrial processes or volcanic eruptions, tend on average to cool it. If positive and negative forcingsremained in balance, there would be no warming or cooling. Source: Intergovernmental Panel on Climate Change.

Figure 4. Model predictions of temperature change much more closely match observed

temperature changes when data from both natural and human-induced causes are used together.

Source: Intergovernmental Panel on Climate Change.

cept of “radiative forcing.” Radiativeforcing is the change in the balance ofradiation (heat and energy) coming intothe atmosphere and radiation going backout. Positive radiative forcings, such asexcess greenhouse gases, tend on averageto warm the Earth, while negative radiative

forcings, such as volcanic eruptions and

many human-produced aerosols, on aver-

age tend to cool the Earth (see Figure 5).

Radiative Forcing of Climate Change:

Expanding the Concept and Addressing

Uncertainties (2005) takes a close look athow climate has been changed by a rangeof forcings. A key message from the reportis that it is important to quantify howthese forcings cause changes in climatevariables other than temperature. Forexample, climate-driven changes in precipitation in certain regions couldhave significant impacts on water avail-ability for agriculture, residential andindustrial use, and recreation. Such region-al impacts will be much more noticeablethan projected changes in global averagetemperature of a degree or more.

Warming will continue, but itsimpacts are difficult to project.The Intergovernmental Panel on ClimateChange (IPCC), which involves hundredsof scientists from the United States andother nations in assessing the state of cli-mate change science, concluded in a 2001report that, by 2100, average global surfacetemperatures will rise 2.5 to 10.4oF (1.4to 5.8oC) above 1990 levels. IPCC also

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WHAT WARMS AND COOLS THE EARTH?The Sun is Earth’s main energy source. Its output appears nearly constant, but small changes during an extended period of time can leadto climate changes. In addition, slow changes in the Earth’s orbit affecthow much of the Sun’s energy reaches the Earth, creating another variable that must be considered.

Greenhouse gases warm the planet:

Water vapor (H2O), supplied from oceans and the natural biosphere,accounts for two-thirds of the total greenhouse effect, but acts primarily as a feedback; water vapor introduced directly to the atmosphere from agricultural or other activities does not stay there very long, and so does not have much warming effect.

Carbon dioxide (CO2) has natural and human sources. CO2 levels are increasing due to the burning of fossil fuels.

Methane (CH4) has been rising from human-caused increases in raising livestock, rice-growing, the production of natural gases, landfills, and other sources.

Ozone (O3) has natural sources especially in the stratosphere, wherechanges caused by ozone-depleting chemicals have been important;ozone also is produced in the troposphere when hydrocarbons and nitrogen oxide pollutants react.

Nitrous oxide (N2O) has been rising from agricultural and industrial sources.

Halocarbons, including chlorofluorocarbons (CFCs), remain from refrigerants in appliances made before CFCs were banned and various similar gases were developed as CFC replacements.

Some aerosols warm the planet:

Black carbon particles or “soot,” produced when fossil fuels or vegetation are burned, have a greenhouse effect, and can enhance absorption of solar radiation.

Some aerosols cool the planet:

Sulfate (SO4) aerosols from burning fossil fuels reflects sunlight back to space.

Volcanic eruptions emit gaseous SO2, which, once in the atmosphere,forms sulfate aerosol and ash. Both reflect sunlight back to space.

Changes in land cover and ice extent can warm or cool the Earth:

Deforestation produces land areas that reflect more sunlight back to space; replacement of tundra by coniferous trees that create darkpatches in the snow cover may increase absorption of sunlight.

Sea ice reflects sunlight back to space; reduction in sea ice extent allows more sunlight to be absorbed into the dark ocean, causing warming.

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Figure 6. More vapor or more clouds? This schematic illustrates just two out of the dozens of climate feedbacks identi-fied by scientists. The warming created by greenhouse gases leads to additional evaporation of water into the atmos-phere. But water vapor itself is a greenhouse gas and can cause even more warming (steps 2-4 are repeated). Scientistscall this “positive water-vapor feedback.” On the other hand, if the water vapor leads to the formation of more clouds,some warming may be counteracted because clouds reflect solar radiation (steps 5-8). Clouds also trap heat in theatmosphere. A major research question is how many and what type of clouds will form—low clouds tend to cool(reflect more energy than they trap) and high clouds tend to warm (trap more energy than they reflect).

concluded that the combined effects ofmelting ice and sea water expansionfrom ocean warming will likely causethe global average sea-level to riseapproximately 0.1 to 0.9 meters between1990 and 2100. Uncertainties remainabout the magnitude, rate, and impactsof future climate change, largely due togaps in understanding climate scienceand the difficulty in predicting futuresocietal choices.

One of the major scientific uncertaintiescurrently being investigated is how

climate could be affected by what are known as “climate feedbacks.”Feedbacks can either amplify or dampenthe climate response to an initial radia-tive forcing (see Figure 6). During a feed-back process, a change in one variable,such as carbon dioxide concentration,causes a change in temperature, whichthen causes a change in a third variable,such as water vapor, which in turn caus-es a further change in temperature.Understanding Climate Change Feedbacks(2003) examines what is known and notknown about climate change feedbacks

and identifies important research avenuesfor improving our understanding.

Another uncertainty is exactly how cli-mate change will affect different regions.Although scientists are starting to projectregional climate impacts, their level ofconfidence is less than for global climateprojections. In general, temperature iseasier to predict than changes such asrainfall, storm patterns, and ecosystemimpacts. It is very likely that increasingglobal temperatures will lead to highermaximum temperatures and fewer colddays over most land areas. Some scientistsbelieve that heat waves, such as thoseexperienced in Chicago and centralEurope in recent years, will continue andpossibly worsen.

Evidence shows that the climate hassometimes changed abruptly in thepast—within a decade—and could do so again. Abrupt changes, such as the Dust Bowl drought ofthe 1930s that displaced hundreds of thousands ofpeople in the AmericanGreat Plains, take place sorapidly that humans and ecosystems have difficulty adapting to them. AbruptClimate Change: InevitableSurprises (2002) outlinessome of the evidence forand theories about abruptchange. One theory is thatmelting ice caps could

“freshen” the water in the North Atlantic, shutting down the naturalocean circulation that brings warmerGulf Stream waters to the north andcooler waters south again (see Figure 7).This shutdown could make it muchcooler in northern Europe.

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Figure 7. A key mechanism in the circulation of water through theworld's oceans is the sinking of cold saltwater. Large oceanic currentstransport warm, saline water to the North Atlantic where the watersbecome denser as they are cooled by cold Arctic air. The chilled seawater sinks to the bottom, forming a southward-moving watermass that flows around Antarctica and fills the world ocean basins.Gradually the water warms, becoming less dense, and returns to thesurface, completing the cycle as it travels northward again. It hasbeen hypothesized that less dense “freshened water” from melting icecaps could disrupt ocean circulation by preventing the formation ofchilled salty water. Such a disruption could trigger a climate changethat would make it cooler in northernEurope. Images courtesy of theMarian Koshland ScienceMuseum of the NationalAcademy of Sciences andthe IntergovernmentalPanel on ClimateChange.

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H O W T H E S C I E N C E I S D O N E

Our ability to look at the Earth as

a whole and model the complex

interactions of the Earth, the

ocean, and the atmosphere is a

very young science, barely 20 years

old. Only in the past few years have

we been able to start making the

links in our science across climate

change, climate variability, regional

climate impacts, to changes in

extreme and episodic events.

—Antonio Busalacchi, Professor,

University of Maryland

Observations and data are the foundation of climate change science.In 1958, long before the idea of human-induced climate change was prevalent, ascientist named Dr. Charles Keeling begancollecting canisters of air a couple times aweek at the Mauna Loa Observatory onthe big island of Hawaii. Keeling’s goalwas to measure carbon dioxide concen-trations to better understand the carboncycle—essentially how carbon isexchanged between plants, animals, theocean, and the atmosphere. This remark-able 50-year dataset has been a boon forclimate change science, and similar obser-vations are now routinely made at stationsacross the globe (see Figure 8).

Unlike many other sciences, where meas-urements can be carefully controlled in the

laboratory, climate change research requiresobservations of numerous naturally occur-ring phenomena over long periods of timeand on a global basis. Climate scientistsmust rely on data collected by a wide arrayof observing systems—from satellites to surface stations to ocean buoys—operated byvarious government agencies and countries,as well as indicators of past climate from icecores, tree rings, corals, and sediments thathelp reconstruct past changes (see Figure 9).

Data should be collected andarchived to meet the uniqueneeds of climate change science.Most of the observing systems used tomonitor climate today were establishedto provide data for other purposes, suchas predicting daily weather; advisingfarmers; warning of hurricanes, torna-does, and floods; managing water

resources; aiding ocean and air trans-portation; and understanding theocean. Collecting climate data, howev-er, is unique: higher accuracy is oftenneeded to detect slow climate trends, theobserving programs must be sustainedover long periods of time and accommo-date changes in observing technology,and observations are needed at bothglobal scales and at local scales to servea range of climate information users.

Many National Academies’ reports on climate change recommend improve-ments to climate observing capabilities.A central theme of Adequacy of ClimateObserving Systems (1999) is the need todramatically upgrade our climateobserving capabilities. The report presents 10 climate monitoring princi-ples that form the basis for designing climate observing systems, includingmanagement of network change, care-ful calibration, continuity of data col-lection, and documentation to ensurethat meaningful trends can be derived.

Another key concept for climate changescience is the ability to generate, ana-lyze, and archive long-term climate datarecords for assessing the state of theenvironment in perpetuity. Climate Data

Records from Environmental Satellites

(2004) defines a climate data record as a time series of measurements of suffi-cient length, consistency, and continuityto determine climate variability andchange. The report identifies several ele-ments of successful climate data recordgeneration programs that range fromeffective, expert leadership to a long-

Figure 8. Collected with the intent of better understanding the carbon cycle,Charles Keeling’s Mauna Loa Curve provides a remarkable set of data onatmospheric carbon dioxide (CO2) concentrations that are now an integral partof climate change science. The steady upward trend shows increases in annualaverage CO2 concentrations due to fossil fuel emissions, and the saw-tooth lineshows the yearly cycle in CO2 concentrations due to seasonal changes inNorthern Hemisphere vegetation. Source: Scripps Institution of Oceanography,University of California, 1998.

Figure 9. (left) Weather balloons, one of theinstruments known as radiosondes, measure temperature, humidity, gases, and other properties throughout the vertical extent of the atmosphere. Image © University Corporation forAtmospheric Research. (top right) Ice is one of Earth’s best record keepers,revealing features of the climate when theice was deposited. Tree rings and sedimentsalso hold past climate information. (bottom right) The Landsat satellite seriesprovides the longest continuous record ofthe Earth's continental surfaces—datingback to 1972—providing critical informa-tion for global change research. Image courtesy of the NASA Goddard Space Flight Center.

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term commitment to sustaining observa-tions and archives.

Models integrate our knowledgeand data on climate change.An important concept that emerged fromearly climate science was that Earth’snatural climate is not just a collection oflong-term weather statistics, but ratherthe complex interactions or “couplings”of the atmosphere, the ocean, the land,ecosystems, and human life. Climatemodels are built using our best scientificknowledge, first modeling each compo-nent separately and then linking themtogether to simulate these couplings.

Climate models are important tools forunderstanding how the climate operatestoday, how it may have functioned dif-

ferently in the past, and how it mayevolve in the future in response to forc-ings from both natural processes andhuman activities. Climate scientists canbetter characterize uncertainty aboutfuture climate by running models withdifferent assumptions of future popula-tion growth, economic development,energy use, and policy choices, such as those that influence how nations sharetechnology. Such models offer a range ofoutcomes based on differing assump-tions (see Figure 10).

Modeling capability and accuracykeep improving. Since the late 1960s and 1970s whenclimate models were pioneered, theiraccuracy has improved as the numberand quality of observations have

Figure 10. Climate models are often used tohelp inform policy decisions. The figureshows the projected global mean temperature change for several different scenarios of future emissions based onassumptions of future population growth, economic development, life style choices, technological change, and availability ofenergy alternatives. Each line represents theaverage of many different models run for thesame scenario. Each model incorporates different assumptions to handle uncertaintiesin our understanding of natural climateprocesses. Source: Intergovernmental Panelon Climate Change (IPCC)

increased, as computational abilitieshave multiplied, and as our theoreticalunderstanding of the climate system hasgrown. Today’s models are very sophisti-cated and able to simulate hundreds ofclimate processes.

The long time scales of climate changemake it difficult to verify models againstactual climate conditions. In contrast, theaccuracy of weather models that forecastconditions only days to weeks in advancecan more easily be checked againstobserved conditions and improved.Climate scientists are now using models towork toward “seamless” predictions fromweather (days) to long-term climatechange (centuries). Successful predictionsof multiyear variabilities known to influ-ence weather, such as the El Niño phenomenon—a natural variation thataffects weather during a 3-7 year cycle—could provide a needed link to moreconfidently projecting climate changesto a decade or longer.

Improving Effectiveness of U.S. ClimateModeling (2001) offers several recom-mendations for strengthening climatemodeling capabilities, some of whichhave already been adopted in the UnitedStates. At the time the report was pub-lished, U.S. modeling capabilities werelagging behind several other nations.The report identified a shortfall in computing facilities and highly skilled technical workers devoted to climatemodeling as two primary causes. Federal

agencies have begun to centralize theirsupport for climate modeling efforts at the National Center for AtmosphericResearch (NCAR) and the GeophysicalFluid Dynamics Laboratory (GDFL).However, as recommended in PlanningClimate and Global Change Research(2003), the United States could stillmake good use of additional resourcesfor climate modeling.

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FEDERALLY COORDINATED RESEARCH ON CLIMATE CHANGEMore than a dozen federal agencies are involved in producingand using climate change data and research. The first efforts ata coordinated government research strategy culminated in thecreation of the U.S. Global Change Research Program (GCRP) in1989. The GCRP coordinated research at these agencies with theaim of “understanding and responding to global change,including the cumulative effects of human activities and natu-ral processes on the environment.” GCRP made substantialinvestments in understanding the underlying processes of climate change, documenting past and ongoing global change,improving modeling, and enhancing knowledge of El Nino andthe ability to forecast it.

In February 2002, President George W. Bush formed the U.S.Climate Change Science Program (CCSP) (http://www.climate-science.gov/) as a new management structure intended toincorporate the work of the GCRP as well as a new ClimateChange Research Initiative (CCRI) that was created to focus onpriority research areas and provide useful information for poli-cy decisions. In fall 2002, the CCSP asked the NationalAcademies to review its draft 10-year strategic plan for climateand global change research. Planning Climate and GlobalChange Research (2003) offered many recommendations forimproving the draft plan. The revised plan, reviewed inImplementing Climate and Global Change Research (2004),was found to be significantly improved.

Climate change impacts will beuneven. Climate change will affect ecosystemsand human systems—such as agricultural,coastal, transportation, and health infra-structure—in ways that we are only beginning to understand (see Figure 11).There will be winners and losers fromthe impacts of climate change, evenwithin a single region, but globally thelosses are expected to far outweigh thebenefits. The larger and faster thechanges in climate, the more difficult itwill be for human and natural systems toadapt without adverse effects.

Unfortunately, the regions that will bemost severely affected are often theregions that are the least able to adapt.Bangladesh, one of the poorest nationsin the world, is projected to lose 17.5%of its land if sea level rises about 40inches (1 meter), displacing millions of people. Several islands throughout the South Pacific and Indian oceans will beat similar risk of increased flooding and

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H O W T H E S C I E N C E I N F O R M S

D E C I S I O N - M A K I N G

Policymakers look to climate change

science to answer two big questions:

what could we do to prepare for

the impacts of climate change, and

what steps might be taken to slow it?

—Richard Alley, Professor,

Pennsylvania State University

The Chinstrap penguin: a regional winner.Even within a single regional ecosystem, there will be winners and losers.

For example, the population of Adélie penguins has decreased 22% during the last 25 years, while the Chinstrap penguin population increased by 400%. The two species depend on different habitats for

survival: Adélies inhabit the winter ice pack, whereas Chinstraps remain in close association with open water. A 7–9° F rise in midwinter temperatures

on the western Antarctic Peninsula during the past 50 years and associated receding sea-ice pack is reflected in their changing populations.

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vulnerability to storm surges. Coastalflooding will likely threaten animals,plants, and fresh water supplies. Tourismand local agriculture could be severelychallenged.

Many developed nations, including theUnited States, are also threatened.Nations with wealth have a betterchance of using science and technologyto anticipate, mitigate, and adapt to sea-level rise, threats to agriculture, andother climate impacts. Adaptations couldinclude revising construction codes incoastal zones or developing new agricul-tural technologies. The developed worldwill need to assist the developing nationsto build their capacity to meet the chal-lenges of adapting to climate change.

We can better prepare for climate change.Climate information is becomingincreasingly important to public and pri-vate decision making in various sectors,such as emergency management, waterquality, insurance, irrigation, power production, and construction. MakingClimate Forecasts Matter (1999) identi-fies research directions toward more use-ful seasonal-to-interannual climate fore-casts and how to use forecasting to bet-ter manage the human consequences ofclimate change.

One way to begin preparing for climatechange is to make the wealth of climate

data and information already collectedmore accessible to a range of users whocan apply it to make informed decisions.Such efforts, often called “climate services,” are analogous to the efforts ofthe National Weather Service to provideuseful weather information. A ClimateServices Vision (2001) outlines principlesfor improving climate services: climatedata should be made as user-friendly asweather information is today, and the gov-ernment agencies, businesses, and univer-sities involved in climate change data col-lection and research today should estab-lish active and well-defined connections.

Another way to prepare for climatechange is to develop practical strategiesthat could be used to reduce economicand ecological systems’ vulnerabilities tochange. Such “no-regrets” strategies pro-vide benefits whether a significant climate change ultimately occurs or not,

Figure 11. Climate changes could have potentially wide-ranging effects on both the natural environment and human activities and economies.

Source: U.S. Environmental Protection Agency.

potentially reducing vulnerability at littleor no net cost. No-regrets measurescould include low-cost steps to improveclimate forecasting; to slow biodiversityloss; to improve water, land, and air qual-ity; and to make our health care enter-prise, financial markets, and transportationsystems more resilient to major disruptions.

Steps can be taken to reducegreenhouse gases in the atmosphere.Despite remaining unanswered ques-

tions, the scientific understanding of cli-mate change is now sufficiently clear tojustify taking steps to reduce the amountof greenhouse gases in the atmosphere.Because carbon dioxide and some othergreenhouse gases can remain in theatmosphere for many decades, centuries,or longer, the climate change impactsfrom concentrations today will likelycontinue well beyond the 21st centuryand could potentially accelerate. Failureto implement significant reductions innet greenhouse gas emissions will makethe job much harder in the future—bothin terms of stabilizing their atmosphericabundances and in terms of experienc-ing more significant impacts.

Governments have proven they can worktogether successfully to reduce or reversenegative human impacts on nature. Aclassic example is the successful interna-tional effort to phase out of the use ofchlorofluorocarbons (CFCs) in aerosolsand refrigerants that were destroying theEarth’s protective ozone layer. At the pres-ent time there is no single solution thatcan eliminate future warming. As early as1992, Policy Implications of GreenhouseWarming found that there are manypotentially cost-effective technologicaloptions that could help stabilize green-house gas concentrations. Personal,national, and international choices couldhave an impact; for example driving less,regulating emissions, and sharing energytechnologies could be beneficial.

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Climate and Human HealthClimate change will likely affect human health in the future.Potential impacts include heat stress, increased air pollution,and lack of food due to drought or other agricultural stresses.Climate change can also influence the spread of infectious diseases. Temperature, precipitation, and humidity can affectthe lifecycle of many disease pathogens and carriers, modifying the timing and intensity of disease outbreaks. Forexample, some studies have predicted that global climatechange could lead to a widespread increase in malaria trans-mission by expanding mosquito habitat and range.

Current strategies for controlling infectious disease epidemicsrely primarily on surveillance and response. Under theWeather: Climate, Ecosystems, and Infectious Disease (2001)recommends a shift toward prediction and prevention, such asdeveloping early warning systems. The report recommendsthat, in order to better understand the linkages between climate change and disease, efforts should be focused onimproving disease transmission models and epidemiologicalsurveillance programs, and increasing interdisciplinary collaboration among climate modelers, meteorologists, ecolo-gists, social scientists, and medical and health professionals.Overall vulnerability to infectious disease could be reducedthrough water treatment systems, vaccination programs, andenhanced efforts to control disease carriers.

Meeting energy needs is the single greatest challenge to slow-ing climate change.Energy—either in the form of fuels useddirectly (such as gasoline) or as electricityproduced using various fuels (such as fos-sil fuels, nuclear, solar, wind, and oth-ers)—is essential for all sectors of theeconomy including industry, commerce,homes, and transportation. Worldwideenergy use continues to grow with eco-nomic and population expansion.Developing countries, China and India inparticular, are rapidly increasing their useof energy, primarily from fossil fuels, andconsequently their emissions of CO2 (see

Figure 12). Carbon emissions from energycan be reduced by using it more efficient-ly or by switching to alternative fuels.

Energy efficiency in all sectors of theU.S. economy could be improved. Gainsmade in response to the oil price shocksof the 1970s slowed as energy prices fell,but many technologies could be imple-mented, especially if current high pricesprove permanent. Effectiveness andImpact of Corporate Average FuelEconomy (CAFE) Standards (2002) eval-uates car and light truck fuel use andanalyzes how fuel economy could beimproved. Steps range from improvedengine lubrication to hybrid vehicles.Energy Research at DOE: Was It Worth It?(2001) addresses the benefits of increas-ing the energy efficiency of lighting,refrigerators, and other appliances. Many

of these improvements are cost-effectivemeans to significantly reduce energy use,but are being held back by market con-straints such as consumer awareness,higher initial costs, and the lack of indus-try incentives and effective policy.

Electricity can be produced without sig-nificant carbon emissions using nuclearpower and renewable energy technolo-gies, such as solar, wind, and biomass. Inthe United States, these technologies arecurrently too expensive or have environ-mental or other concerns that limit broadapplication; however, this could changeif new technologies develop or as thecosts of fossil fuels increase. Replacingcoal-fired electric power plants withmore efficient, modern natural-gas-firedturbines would reduce carbon emissionsper unit of electricity produced.

Another way to reduce emissions is tocollect CO2 emitted to the atmospherefrom fossil-fuel-fired power plants, andthen sequester it in the ground or the ocean. Novel Approaches to CarbonManagement: Separation, Capture,

Personal, national, and international choices could havean impact; for example, driving less, regulating emissions,

and sharing energy technologies could be beneficial.

18

Figure 12. The two panels compare CO2 emissions per nation in 2000 and projections for 2025. In 2000, the largest emitter of CO2 was the UnitedStates, which is responsible for 25% of global emissions. In 2025, China and the developing world may significantly increase their CO2 emissionsrelative to the United States. Image courtesy of the Marian Koshland Science Museum of the National Academy of Sciences.

Sequestration, and Conversion to UsefulProducts (2003) discusses the develop-ment of this technology. If successful,carbon sequestration could weaken thelink between fossil fuels and greenhousegas emissions.

Capturing CO2 emissions from thetailpipes of vehicles is essentially impos-sible, which is one factor that has led toconsiderable interest in hydrogen as afuel. However, as with electricity, hydro-gen must be manufactured from primaryenergy sources. Significantly reducingcarbon emissions when producinghydrogen from fossil fuels (currently theleast expensive method) would requirecarbon capture and sequestration.Substantial technological and economicbarriers in all phases of the hydrogenfuel cycle must first be addressedthrough research and development. TheHydrogen Economy: Opportunities,Costs, Barriers and R&D Needs (2004)presents a strategy that could lead eventu-ally to production of hydrogen from a vari-

ety of domestic sources—such as coalwith carbon sequestration, nuclear power,wind, or photo-biological processes—andits efficient use in fuel-cell vehicles.

Continued Scientific Efforts toAddress a Changing ClimateAlthough society’s understanding of climate change has advanced signifi-cantly during the past few decades,many questions remain unanswered.The task of mitigating and preparing forthe impacts of climate change willrequire worldwide collaborative inputsfrom a wide range of experts, includingnatural scientists, engineers, social scientists, medical scientists, businessleaders and economists. Society facesincreasing pressure to decide how bestto respond to climate change and associated global changes, and appliedresearch in direct support of decisionmaking is needed. In particular, researchshould explore response options andevaluate the costs and benefits of adapt-ing to and slowing climate change.

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Thinking Strategically: The Appropriate Use of Metrics for the Climate Change Science Program (2005)Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005)Climate Data Records from Environmental Satellites (2004)Implementing Climate and Global Change Research: A Review of the Final U.S. Climate Change Science

Program Strategic Plan (2004)A Vision for the International Polar Year 2007-2008 (2004)The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs (2004)Understanding Climate Change Feedbacks (2003)Planning Climate and Global Change Research: A Review of the Draft U.S. Climate Change Science

Program Strategic Plan (2003)Novel Approaches to Carbon Management: Separation, Capture, Sequestration, and Conversion to Useful

Products (2003)Abrupt Climate Change: Inevitable Surprises (2002)Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (2002)Climate Change Science: An Analysis of Some Key Questions (2001)Improving the Effectiveness of U.S. Climate Modeling (2001)A Climate Services Vision: First Steps Towards the Future (2001)Energy Research at DOE: Was It Worth It? (2001)Reconciling Observations of Global Temperature Change (2000)Adequacy of Climate Observing Systems (1999)Making Climate Forecasts Matter (1999)Policy Implications of Greenhouse Warming (1992)

For more studies and related information see http://dels.nas.edu/ccgc and http://www.nationalacade-mies.org/basc. National Academies reports are available from the National Academies Press, 500 FifthStreet, NW, Washington, DC 20001; 800-624-6242; http://www.nap.edu. Reports are available onlinein a fully searchable format.

SELECTED CLIMATE CHANGE AND RELATEDREPORTS FROM THE NATIONALACADEMIES

About the National AcademiesThe National Academies are nongovernment, nonprofit organizations that were set up to pro-vide independent scientific and technological advice to the U.S. government and nation. TheNational Academies includes three honorary societies that elect new members to their rankseach year—the National Academy of Sciences, National Academy of Engineering, andInstitute of Medicine—and the National Research Council, the operating arm that conductsthe bulk of the institution's science policy and technical work. The Academies enlist com-mittees of the nation's top scientists, engineers, and other experts, all of whom volunteer theirtime to study specific issues and concerns.

The National Academies offers the following e-mail newsletters and notifications related toclimate change:

Earth & Life Studies at the National Academies, http://dels.nas.edu (immediate notification of new projects, committee postings, reports, and events)

Climate and Global Change at the National Academies e-update, http://dels.nas.edu/ccgc (monthly)

The Board on Atmospheric Sciences and Climate Newsletter, http://dels.nas.edu/basc (quarterly)

For more information, contact the Board on Atmospheric Sciences and Climate at 202-334-3512 or visit http://dels.nas.edu/basc. This brochure was prepared by the National ResearchCouncil based on National Academies’ reports. It was written by Amanda Staudt, NancyHuddleston, and Sandi Rudenstein and was designed by Michele de la Menardiere. Supportfor this publication was provided by the Presidents’ Circle Communications Initiative of theNational Academies.

OCTOBER 2005. COPYRIGHT 2005 THE NATIONAL ACADEMY OF SCIENCES.

At a time when responding to our changing climate is one of the nation’s

most complex endeavors, reports from the National Academies provide

thoughtful analysis and helpful direction to policymakers and stakeholders.

These reports are produced by committees organized by the Board on

Atmospheric Sciences and Climate, its Climate Research Committee, and

numerous other entities within the National Academies. With support from

sponsors, the National Academies will continue in its science advisory role

to the agencies working on understanding changing climate, documenting its

impacts, and developing effective response strategies.

U N D E R S T A N D I N G A N D R E S P O N D I N G T O

CLIMATECHANGE

H i g h l i g h t s o f

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Institute of MedicineNational Research Council