CLIMATE CHANGE State of Knowledge The Office of Science and Technology Policy (OSTP) was established by the National Science and Technology Policy, Organization, and Priorities Act of 1976. OSTP is responsible for advising the President on all questions in which science and technology are important elements, including climate change. CLIMATE CHANGE State of Knowledge October 1997 ground During the 1980s, sdentific evidence about globat climate change an,d its con"uences led to growing concern among. ientisU. ra,akers,,AW the d process, s io countries MEM n on climate economic effects an Ve' ided the scientific understanding needed to help formulate appropriate responses. A series of IPCC reports, incorporating extensive peer review and a commitment to scientific excellence, have provided the most authoritative and comprehensive information available on the science of climate change. In 1996, the IPCC published its Second Assessment Report., whi*F"mmarý m, m, - gpost recent infor gg and the vulnermation o V k" 0". VIM *0,121;M,1_11, Aft g,%r--,, ability of F ds4ffiaaiýýic systems. lPCC Website: http-://www.lpcc.ch/ In 1990. the United Nations (UN) General Assembly established the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change (FCCC). The FCCC was adopted in 1992, and over 160 signatories have now become parties to the agreement. The agreement was signed by the President of the U.S. and ratified by the U.S. Senate in 1992. The ultil" cjim of the FCCC is to staWlize greenhouse,, M'i.k r, entrations "rat a level Vu*,,ý Ood-,pre, anthrosystem. ~r..' -Tw- oW bet within a ti 1) allows ec&yftems to adapt nat I ate change, (2) ensures that food production is not threatened, and (3) enables sustainable economic development to proceed. Introducti"on Burning coal, oil and natural gas to heat our over the last century, and that "the balance homes, power our cars, and illuminate our of evidence suggests that there is a discities produces carbon dioxide (C02) and cernible human influence on global cliother greenhouse gases as by-products. mate." Deforestation and clearing of land for agriculture also release significant quantities of such The IPCC estimates that global surface air gases. Over the last century, we have been temperature will increase another 2 - 6.5* F emitting greenhouse gases to the atmosphere in the next 100 years. The difference in faster than natural processes can remove temperature from the last ice age to now is them. During this time, atmospheric levels of about 9* F. Their "best guess" is that we will these gases have climbed steadily and are pro- experience warming of about 3.5' F by 2100, jected to continue their steep ascent as global which would be a faster rate of climate economies grow. change than any experienced during the last 10,000 years, the period in which modern Records of past climate going as far back as civilization developed. 160,000 years indicate a close correlation between the concentration of greenhouse Warming of this magnitude will affect many gases in the atmosphere and global tempera- aspects of our lives as it changes temperatures. Computer simulations of the climate ture and precipitation patterns, induces sea indicate that global temperatures will rise as level rise, and alters the distribution of fresh atmospheric concentrations of C02 increase, water supplies. The impacts on our health, Thie 1995 report of the Intergovernmental the vitality of forests and other natural Panel on Climate Change (IPCC), which is areas, and the productivity of agriculture are the most comprehensive and thoroughly all likely to be significant. As the risks of reviewed assessment of climate change sci- global climate change become increasingly ence ever produced, concluded that change is apparent, there is a genuine need to focus alread underway.--1-- The IPCC, whc repre-1-__- on acton to reuc our grehos gas-_ _--1-------_ - --_ ---- The Greenhouse Effect and Historical Emissions Life as we know it is possible on Earth because industrialization and population growth, greenof a natural greenhouse effect that keeps our house gas emissions from human activities have planet about 60' F warmer than it otherwise consistently increased. These steady additions would be (Figure 1). Water vapor, carbon diox- have begun to tip a delicate balance, signifiide (CO2), and other trace gases, such as cantly increasing the amount of greenhouse methane and nitrous oxide, trap solar heat and gases in the atmosphere, and enhancing their slow its loss by re-radiation back to space. With insulating effect. ab B nfrared radiation ~itted from the Figure 1. The greenhouse effect naturally warms the Earth's surface. Without it, Earth would be 600 F cooler than it is today - uninhabitable for life as we know it. 2 A wide variety of activities contribute to greenhouse gas emissions. Burning of coal, oil, and natural gas releases about 6 billion tons of carbon into the atmosphere each year worldwide. Figure 2. Burning fossil fuels such as coal, oil, and Burning and logging of forests contributes Figure 2. Burning fossil fuels anoter -2 illon onsannall byredcin gas, add 6 billion metric tons of carbon each year another 1-2 billion tons annually by reducing to the atmosphere. the storage of carbon by trees (Figures 2 and 3). Figure 3. Deforestation worldwide adds 1 to 2 billion metric tons of carbon to the atmosphere each year. 3 The result is that the atmospheric level of C02, The overall emissions of greenhouse gases are the most important human-derived greenhouse growing at about 1 percent per year. For millengas, has increased 30 percent, from 280 to 360 nia, there has been a clear correlation between parts per million (ppm) since 1860 (Figure 4). C02 levels and the global temperature record. Over the same time period, agricultural and Fluctuations of C02 and temperature have industrial practices have also substantially roughly mirrored each other over the last increased the levels of other potent greenhouse 160,000 years (Figure 5). The current level of gases -- methane concentrations have doubled C02 is already far higher than it has been at and nitrous oxide levels have risen by about 15 any point during this period. If current emispercent. These gases have atmospheric lifetimes sions trends continue over the next century, ranging from decades to centuries; today's emis- concentrations will rise to levels not seen on sions will be affecting the climate well into the the planet for 50 million years. 21st century. Figure 4. Since the beginning of the Industrial Revolution in the middle of the 19th century, the concentration of carbon dioxide (C02) in the atmosphere has steadily increased. Beginning in 1957, continual measurements of atmospheric C02 concentrations have been made by scientists at an observatory in Mauna Loa, Hawaii. The seasonal cycle of vegetation in Northern latitudes can be seen in this record: each spring the vegetation "inhales" and absorbs C02, and each autumn most of that C02 is released back to the atmosphere. 4 Figure 5. Data from tiny air bubbles trapped in an Antarctic ice core show that atmospheric C02 concentrations and temperatures from 160,000 years ago to pre-industrial times are closely correlated. Direct measurement of C02 concentration and temperature in recent decades extend this record to the present day, and confirm that C02 concentrations have risen to 360 ppm and temperatures have increased 0.5 degree C (1 degree F) over the last 100 years. 5 Which countries account for the largest pro- tries, some of which are also undergoing rapid portions of C02 emissions? In 1995, 73 per- economic development. Per capita energy use cent of the total C02 emissions from human in the developing countries, which is currently activities came from the developed countries only 1/10 to 1/20 of the U.S. level, will also (Figure 6). The United States is the largest sin- increase. If current trends continue, the develgle source, accounting for 22 percent of the oping countries will account for more than half total, with carbon emissions per person now of total global C02 emissions by 2035. China, exceeding 5 tons per year. Over the next few which is currently the second largest source, is decades, 90 percent of the world's population expected to have displaced the United States as growth will take place in the developing coun- the largest emitter by 2015. Figure 6. In 1995, the industrialized nations of the world contributed nearly three-quarters of the global emissions of carbon dioxide, with the U.S. being the largest single emitter. By 2035, developing nations will catch up and contribute half of the global emissions, with China becoming the largest single emitting country. Rapid population growth, industrialization, and increasing consumption per person in the developing world will contribute to this shift. 6 Asia 6% mrca 4% ca 3 Asa 6% Afia. Othe Asi 14MUA5 Figure~ ~ ~ ~ ~ ~ ~ ~~ ~~W 6.I 95 h nutilzdntoso h olotiue Ealthe-uaropers thhlba msionsocaro dixie wtthU..bighelrstiNAl Mite.B 5 Climate Change Over the Last 100 Years Global surface temperature has been measured parts of the Earth system (the surface, and varisince 1880 at a network of ground-based and ous layers of the atmosphere). In addition to ocean-based sites. Over the last century, the this, a variety of factors, such as the presence of average surface temperature of the Earth has airborne materials from the 1991 eruption of increased by about 1.0' F. The eleven warmest the volcano Mt. Pinatubo, affect each record in years this century have all occurred since 1980, a different way. Satellite observations were iniwith 1995 the warmest on record (Figure 7). tially interpreted as showing a slight cooling, The higher latitudes have warmed more than but more recent analyses accounting for naturthe equatorial regions. al, short-term fluctuations imply warming, just as the ground-based measurements have indiBeginning in 1979, satellites have been used to cated over a longer time period. As more data measure the temperature of the atmosphere up from the satellite record become available, and to a height of 30,000 feet. The long-term sur- as the quality of measurements is improved, face record and the recent satellite observations comparison of these two records should yield differ, but that fact is not surprising: the two additional insights. techniques measure the temperature of different Figure 7. The global average temperature has risen by approximately 10 F over the last century. 7 What does warming do? A warmer Earth Global mean sea level has risen 4 to 10 inches speeds up the global water cycle: the exchange over the last 100 years, mainly because water of water among the oceans, atmosphere, and expands when heated. The melting of glaciers, land. Higher temperatures cause more evapora- which has occurred worldwide over the last tion, and soils will tend to dry out faster, century, also contributes to the rise. Formerly Increased amounts of water in the atmosphere frozen soils (permafrost) in the Alaskan and will mean more rain or snow overall. Siberian arctic have also begun to melt, damaging both ecosystems and infrastructure. We may be seeing the first signs of changes in Melting and tundra warming will also lead to the water cycle. Since the beginning of the cen- decay of organic matter and the release of tury, precipitation in the United States has trapped carbon and methane, creating an addiincreased by about 6 percent, while the fre- tional source of greenhouse gases. quency of intense precipitation events (heavy downpours of more than two inches per day) has increased by 20 percent. Such events can cause flooding, soil erosion, and even loss of life (Figures 8 and 9). In some midcontinental areas, increased evaporation has led to drought because the heavy rains fell elsewhere. There is also evidence that ecosystems are reacting to warming. Between 1981 and 1991, the length of the growing season in the northern high latitudes (between 450 and 700 N) increased by a total of up to twelve days, as documented by satellite imagery. "Greening" in spring and summer occurred up to eight days earlier, and vegetation continued to photosynthesize an estimated four days longer. Figure 8 and 9. Our society is already vulnerable to extreme weather events such as floods. These images show the devastating effects of the 1993 Mississippi River flood on St. Louis, Missouri. Climate change is likely to increase the frequency of severe flood events. Cli*mate Change Over the Next 100 Years Where is the climate headed? If the AmshrcCro ixd ocnrto world proceeds on a "business as175 usual" path, atmospheric C02 concentrations will likely be more than 700 ppm by 2100, and they will still be rising. This is nearly double the cur-70 rent level and much more than double the preindustrial level of 280 ppm (Figure 10). State-of-the-art climate models suggest that this will result in an increase of about 3.*5 F in global temperatures over the next century.60 This would be a rate of climate change not seen on the planet for at least the last 10,000 years. It is the combined threat of elevated concentrations of greenhouse gases and this unprecedented rate of increase that causes great concern.50 What are the projected extent and pattern of warming over the globe? The higher latitude regions will warm relatively more than areas nearer to the equator. The land surface will warm more than the oceans, and there will be less variation in temperature from night to day.Curn Figur 10.The 02 lvel as icreaedLsarpl since ~ ~ ~ ~ ~ ~ ~ ~ ~ 0 th0einn fteInutilEaadi Even if the rate of emissions is slowed enough to limit atmospheric concentrations to about 550 ppm, or roughly double the preindustrial level, the U.S. could experience temperature increases of 5* F to 100 F (Figure 11). These warmer temperatures would lead to soil drying in some regions, with drying estimated at 10 percent to 30 percent for the United States during the summer growing season (Figure 12). Figure 12. The extent of warming indicated in Figure 11 will lead to substantial soil drying throughout the world, causing soil moisture decreases of 10 percent to 30 percent over North America. Figure 11. Even if C02 levels only rise to 560 ppm by the year 2100, U.S. temperatures will eventually be about 5-10 degrees F warmer than today. Higher latitudes will warm more than equatorial regions. 10 Some modeling experiments have examined the consequences of C02 levels well beyond 700 ppm, which are likely to occur after 2100 if current emissions trajectories are not altered. If the C02 concentration were to continue to rise to four times the preindustrial level, or more than 1100 ppm, the estimated temperature increase for the United States would be 15' F to 20* F, and soil drying could approach 30 percent to 50 percent during the growing season (Figures 13 and 14). Figure 13 The extent of warming indicated in Figure 14 would lead to severe soil drying in the U.S., with deficits reaching 30 percent to 50 percent during the growing season. Figure 14. If the C02 levels reach 1100 ppm, U.S. temperatures could be 15 'F to 20 TF higher than current levels. 11 Vulnerabili*ti*es and Potenti*al Consequences The climate changes expected from increased day and night. Today, such events occur about atmospheric concentrations of greenhouse gases once every 150 years. C02 concentrations of50 are likely to have widespread effects, many of ppm (double the pre-industrial level) could mak them negative, on ecological systems, human such events 6 times more frequent. The potenhealth, and socioeconomic sectors. In general, tial increases in the heat index, a calculation people in developing countries are more vulner- combining temperature and humidity, illustrate able to climate change because of limited infra- the magnitude of this threat. Washington, D.C structure and capital and greater dependence on currently has an average July heat index of 85.1F natural resources. Unless otherwise specified, but if C02 levels reach 550 ppm, this could the impacts and vulnerabilities discussed below increase to 95" F, and if concentrations quadruare based on scenarios of doubling of current pled to 1100 ppm, it could increase to 1 10" F. levels of C02 by 2100 (700 ppm). Beyond such Climate change will also exacerbate air quality concentrations, impacts appear to worsen, but problems, such as smog, and increase levels of uncertainty about what will happen increases, airborne pollen and spores that aggravate respia In general, uncertainty cuts both ways: out- tory disease, asthma, and allergic disorders comes could be less dramatic than expected (Figure 15). Because children and the elderlyar based on our current understanding, but could the most vulnerable populations, they are likel just as well be much more severe, to suffer disproportionately with both warmer. temperatures and poorer air quality. Worsening Health Effects - Climate change will impact human health in a variety of ways. Diseases that thrive in warmer climates, such a Warmer temperatures increase the risk of mor- malaria, dengue and yellow fevers, encephalitis tality from heat stress. For example, in July and cholera, are likely to spread due to the 1995, 465 deaths in Chicago were attributed to expansion of the ranges of mosquitos and othe a heat wave with temperatures exceeding 900 F di seas e-carrying organisms and increased rateso transmission. This could result in 50 million to ally exceed 40 inches. A CO2 level of 1100 ppm 80 million additional malaria cases per year could produce a sea level rise of 80 inches or worldwide by 2100. even more, depending on the extent to which the Greenland and Antarctic ice sheets melt. Rising Sea Level - Rising sea level erodes beaches and coastal wetlands, inundates low- * A 20-inch sea level rise would double the lying areas, and increases the vulnerability of global population at risk from storm surges, coastal areas to flooding from storm surges and from roughly 45 million at present to over 90 intense rainfall. By 2100, sea level is expected million, and this figure does not account for to rise by 6 to 37 inches. A 20-inch sea level any increases in coastal populations. A 40 -rise will result in substantial loss of coastal land inch rise would triple the number. in the United States, especially along the southern Atlantic and Gulf coasts, which are subsid- * South Florida is highly vulnerable to sea level ing and are particularly vulnerable. The oceans rise (Figure 16). A third of the Everglades has will continue to expand for several centuries an elevation of less than 12 inches. Salt water after temperatures stabilize. Because of this, the intrusion would adversely affect delicate ecosea level rise associated with CO2 levels of 550 logical communities and degrade the habitat ppm (double pre-industrial levels) could eventu- for many species. Figure 16. Sea level rise could inundate many low-lying coastal areas in Florida, and will increase the vulnerability of all such areas to storm surges. 13 Disruption of the Water Cycle - Among the most fundamental effects of climate change are intensification and disruption of the water cycle. Droughts and floods - Intensification of the water cycle will produce more severe droughts in some places and floods in others. Such events are costly. Damages from the Southern Plains drought of 1996 were estimated at $4 billion, the 1993 Mississippi River flood damages at $10 billion to $20 billion, the Pacific Northwest floods in the winter of 1996-1997 at about $3 billion, the 1997 Ohio River flood at about $1 billion, and the 1997 Red River flood in the Northern Plains at about $2 billion. Water quality and quantity - Areas of greatest vulnerability are those where quality and quanFigure 17. Severe drought will become more frequent in tity of water are already problems, such as the some regions as the precipitation patterns shift. arid and semi-arid regions of the United States and the world (Figure 17). Figure 18. Climatic shifts will force some species to migrate northwards or to higher elevations in order to stay in the appropriate climatic zone. The climatic zone for sugar maple, for example, could shift northwards into Canada. This would compromise the maple syrup industry and the fall foliage colors, both of which make New England famous. 14 * Climate change would likely increase water far faster than the forests can migrate naturally. supply problems in several U.S. river basins, Economically important species, such as the such as the Missouri, Arkansas, Texas Gulf, sugar maple, could be lost from New England Rio Grande, and Lower Colorado. by the end of the next century (Figure 18). * Water scarcity in the Middle East and Africa Such changes could have profound effects on is likely to be aggravated by climate change, the U.S. system of national parks and refuges, which could increase international tension leading to reductions in biological diversity and among countries that depend on water sup- in the benefits provided by ecosystems, such as plies originating outside their borders. clean water and recreation. Wetlands are particularly at risk. The wetlands of the prairie potChanging Forests and Natural Areas - hole region, which support half the waterfowl Climate change could dramatically alter the population of North America, could diminish in geographic distributions of vegetation types. area and change dramatically in character in The composition of one-third of the Earth's response to climate change. The glaciers of forests would undergo major changes as a result Glacier National Park have receded steadily for of climate changes associated with a CO2 level decades (Figure 19). Model projections indicate of 700 ppm. Over the next 100 years, the ideal that all the Park's glaciers will disappear by range for some North American forest species 2030 unless temperatures begin to cool instead will shift by as much as 300 miles to the north, of warm. II 1850 1979 Figure 19. Warmer temperatures have already led to substantial glacier melting and shrinkage in Glacier National Park, Montana. Data indicate that more than 70 percent of some of the glaciers in the National Park have already melted. 15 Challenges to Agriculture and the Food these effects, total global food production is not Supply - Climate strongly affects crop yields. expected to be altered substantially by climate A CO2 concentration of 550 ppm is likely to change, but there are likely negative regional increase crop yields in some areas by as much impacts. Agricultural systems in the developed as 30 percent to 40 percent, but it will decrease countries are highly adaptable and can probably yields in other places by similar amounts, even cope with the expected range of climate changes for the same crop. A warmer climate would without dramatic reductions in yields. It is the reduce flexibility in crop distribution and poorest countries, already subject to hunger, that increase irrigation demands. Expansions of the are the most likely to suffer significant decreases ranges of pests could also increase vulnerability in agricultural productivity (Figure 20). and result in greater use of pesticides. Despite Figure 20. Agricultural production would increase in some areas, and decline in others as the climate warms and the C02 levels in the atmosphere increase. Farmers may need to shift crops, or re-locate agricultural lands. The need for irrigation may also increase. 16 Conclusion As the world's expanding population burns the probable consequences of climate change. large quantities of fossil fuels and simultaneously cuts down large expanses of forests world- On a business as usual path, the world is headwide, the concentrations of CO2 and other ed to concentrations far higher than have been greenhouse gases are building up in the atmos- observed during the time of human civilization phere. There is mounting evidence that this and to levels not seen on the planet for milshift in Earth's atmosphere will lead to global lions of years--and all in one century, a geologic changes and potentially major climatic disrup- "blink of an eye." The faster the rate of change tions. in climate, the less time there will be for both ecological and socio-economic systems to adapt Human and ecological systems are already vul- and the greater the potential for "surprises" or nerable to a range of environmental pressures, unanticipated events. Given the long time lags including climate extremes and variability, between cause and effect and between effect Global warming is likely to amplify the effects and remedy, a prudent course of action is to of other pressures and to disrupt our lives in slow the rate of change. Investing now to pronumerous ways. Significant impacts on.our tect Earth's climate will enable our children and health, the vitality of forests and other natural grandchildren to live in a world that is not draareas, the distribution of freshwater supplies, matically altered by an enhanced greenhouse and the productivity of agriculture are among effect. 17 Credits Figure 1: The Greenhouse Effect Source: ~M. Warford, 1995 Figure 2: Burning fossil fuels photogroph Source: @P. Grabhorn, 1994 Figure 3: Deforestation photograph Source: QP. Grabhorn, 1996 Figure 4: Carbon Dioxide Concentrations, 1860 to present Source: Data from Neftel et a/., 1985; Keeling, 1995 Figure 5: Atmospheric Carbon Dioxide Concentration and Temperature Change Source: Vostok ice core data from Barnola et a/.,, 1987; current data from the Carbon Dioxide Information Analysis Center, 1997, Oak Ridge T Figure 6: Total World Emissions, 1995 and 2035 Source: Carbon Dioxide Information Analysis Center, 1997, Oak Ridge, TN; Edmonds, 1997, Batelle Laboratories, using IPCC IS92A emission scenario Figure 7: Global Average Temperature Source: Data from Hansen et a/.,, 1995, Goddard Institute for Space Studies Figure 8: Mississippi River flood photograph Source: ~P. Grabhorn, 1993 Figure 9: Mississippi River flood Landsat S Thermatic Mapper images Source: (DEOSAT Corporation, 1995, Lanham, MD Figure 10: Atmospheric Carbon Dioxide Concentration and Temperature Changes projected to year 2100 Source: Vostok ice core data from Barnola et al., 1987; current data from the Carbon Dioxide Information Analysis Center, 1997, Oak Ridge TN; 1995 IPCC emission scenarios Figure 11: Surface Air Warming (F), 2xCO2 Source: Manabe and Stouffer, 1994, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ Figure 12: Percent Reduction in June-August Soil Moisture, 2xCO2 Source: Manabe and Stouffer, 1994, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ Figure 13: Percent Reduction in June-August Soil Moisture, 4XCO2 Source: Manabe and Stouffer, 1994, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ Figure 14: Surface Air Warming (F), 4XCO2 Source: Manabe and Stouffer, 1994, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ Figure 15: Urban smog photograph Source: QP. Grabhorn, 1993 Figure 16: South Florida Shoreline Change after a 1 -meter Rise in Sea Level Source: Data from USGS, 1997; Map visualization @C. Grabhorn, 1995 Figure 17: Severe drought in a dry river bed photograph Source: QP. Grabhorn, 1994 Fcmigre 18 Cu r rreont andf Projected Rangeso of Suganr Manpl I AW,,,.. -- o_