The human race is engaged in the largest and most dangerous experiment in history... It is an experiment to see what will happen to our health and the health of our planet when we change our atmosphere and our climate. This is not some deliberate scientific inquiry. It is an uncontrolled experiment on the environment of the Earth, and we're gambling our children's future on its outcome.
The results of this pollution are already significant. We have increased levels of carbon dioxide (CO2) the primary global warming gas, in our atmosphere by 30% in the last 100 years. Some regions of the world have already warmed by as much as 5 degrees Fahrenheit. Physicians at Harvard University and Johns Hopkins Medical Schools and other medical institutions have issued grim assessments that global warming may already be causing the spread of infectious diseases and increasing heat wave deaths. Extreme weather events have become more common. Plants and animals around the world are shifting their ranges in an effort to escape a changing climate.
The rapid buildup of greenhouse gases in our atmosphere is the source of the problem. By burning ever increasing quantities of coal, oil, and gas we are choking our planet in a cloud of this pollution. If we don't begin to act now to curb global warming, our children will live in a world where the climate will be far less hospitable than it is today.
Global warming is a pollution problem. Gas-guzzling cars and light trucks, such as mini-vans and sport utility vehicles, are major sources of this pollution. Over its lifetime, the average car on the road today will spew out 50 tons of carbon dioxide pollution into the air. Raising the fuel economy standards in the US to 45 mpg for cars and 34 mpg for light trucks would keep millions of tons of CO2 out of the atmosphere.
Global warming also comes from burning coal, oil, and to a lesser extent, natural gas, in our power plants. Coal is especially dirty, producing twice as much carbon dioxide per unit of heat produced as natural gas, and a third more than oil.
Trees "breath" carbon dioxide, and can work to clean part of the pollution we release from the air. But when trees are cut down or burned they release their carbon dioxide back into the air. Over-harvesting of the world's forests is a significant contributor to global warming.
For years powerful computers have been used to project the results of global warming. Grim predictions of sea level rise and the spread of infectious disease raised the issue of global warming in the minds of many Americans. Scientists now are becoming increasingly alarmed as more and more of these predictions come true.
Some events computers have predicted which have come true are:
Major shifts in temperature and precipitation. Some parts of the world have warmed by as much as 4.5 degrees Fahrenheit or more in the last 100 years. The average temperature of the planet has risen about 1 degree Fahrenheit.
Shifting ranges of infectious disease, and increasing cases of infection around the world. Dengue fever infected victims in Texas in 1995, and in recent years malaria infections have occurred as far north as New York, New Jersey, and Michigan.
Sea levels rising almost a foot in the last century, destroying beaches and wetlands around the world. Continued warming may mean an additional rise of 2 feet or more and the flooding of huge portions of low-lying states, such as Louisiana and Florida.
Glaciers melting and snow cover disappearing on 5 continents. In 1994, a 48 by 22 mile chunk of the Larsen ice shelf in Antarctica broke off and melted. In 1997, huge crevasses were found indicating the rest of the shelf will soon follow.
Drastic habitat shifts for plants and animals. Scientists have documented shifting populations and altered migration behavior as animals attempt to adapt to a changing climate. Many species that cannot adapt are in decline.
There is also growing evidence of a link between global warming and the recent pattern of more frequent and severe El Nino events. Scientists warn that as global warming worsens, we can expect:
A global warming of up to 6 degrees Farenheit.
Sea levels rising up to two feet.
Major increases in plant and animal extinctions.
More common and severe winter floods and summer droughts.
More common and brutal storms.
Spreading infectious disease.
The projected 2°C (3.6°F) warming could shift the ideal range for many North American forest species by about 300 km (200 mi.) to the north. If the climate changes slowly enough, warmer temperatures may enable the trees to colonize north into areas that are currently too cold, at about the same rate as southern areas became too hot and dry for the species to survive. If the earth warms 2°C (3.6°F) in 100 years, however, the species would have to migrate about 2 miles every year.
Trees whose seeds are spread by birds may be able to spread at that rate. But neither trees whose seeds are carried by the wind, nor such nut-bearing trees such as oaks, are likely to spread by more than a few hundred feet per year. Poor soils may also limit the rate at which tree species can spread north. Thus, the range over which a particular species is found may tend to be squeezed as southern areas become inhospitably hot. The net result is that some forests may tend to have a less diverse mix of tree species.
Several other impacts associated with changing climate further complicate the picture. On the positive side, CO2 has a beneficial fertilization effect on plants, and also enables plants to use water more efficiently. These effects might enable some species to resist the adverse effects of warmer temperatures or drier soils. On the negative side, forest fires are likely to become more frequent and severe if soils become drier. Changes in pest populations could further increase the stress on forests. Managed forests may tend to be less vulnerable than unmanaged forests, because the managers will be able to shift to tree species appropriate for the warmer climate.
Perhaps the most important complicating factor is uncertainty (see US Climate in the Climate Systems section) whether particular regions will become wetter or drier. If climate becomes wetter, then forests are likely to expand toward rangelands and other areas that are dry today; if climate becomes drier, then forests will retreat away from those areas. Because of these fundamental uncertainties, existing studies of the impact of climate change have ambiguous results.
Two different types of computer models have been employed to estimate the impact of climate change on forests: The "biogeography models" analyze the essential environmental conditions over entire continents, to estimate the type of vegetation that is most likely to cover a given area. The "gap models" simulate all of the dynamic relationships (e.g., large trees shading small trees) for small representative areas. Both types of studies generally report the total leaf area of all the trees in a forest.
The biogeography models provide much more optimistic results than the gap models. Biogeography models suggest that if the beneficial effect of carbon dioxide is disregarded, then 12-76% of the mixed evergreen and deciduous forests in the United States would become thinner (i.e., less leaf area), while 2-49% would experience increases by the year 2100. When the likely effect of CO2 fertilization is included, however, less than 7 percent of the mixed forests are likely to decline, and more than 92 percent of those forests are likely to increase. Studies using the gap models, however, suggest that a large number of areas may no longer be able to support forests, particularly if the climate becomes drier.
The potential impacts of climate change on forest wildlife are poorly understood. If habitats simply shift to cooler areas (i.e., higher latitudes or higher altitudes), many forms of wildlife could potentially adapt to global warming, just as they have adapted to the changes in climate that have occurred over the last several million years. Unlike previous climatic shifts, however, roads, development, and other modifications to the natural environment may block the migration routes. Nature reserves, often established to protect particular species, may no longer be located in a climate hospitable to that species.
Throughout the world, the prevalence of particular diseases and other threats to human health depend largely on local climate. Extreme temperatures can directly cause the loss of life. Moreover, several serious diseases only appear in warm areas. Finally, warm temperatures can increase air and water pollution, which in turn harm human health.
The most direct effect of climate change would be the impacts of hotter temperatures themselves. Extremely hot temperatures increase the number of people who die on a given day for many reasons: People with heart problems are vulnerable because one's cardiovascular system must work harder to keep the body cool during hot weather. Heat exhaustion and some respiratory problems increase.
Higher air temperatures also increase the concentration of ozone at ground level. The natural layer of ozone in the upper atmosphere blocks harmful ultraviolet radiation from reaching the earth's surface; but in the lower atmosphere, ozone is a harmful pollutant. Ozone damages lung tissue, and causes particular problems for people with asthma and other lung diseases. Even modest exposure to ozone can cause healthy individuals to experience chest pains, nausea, and pulmonary congestion. In much of the nation, a warming of four degrees (F) could increase ozone concentrations by about 5 percent.
Statistics on mortality and hospital admissions show that death rates increase during extremely hot days, particularly among very old and very young people living in cities. In July 1995, a heat wave killed more than 700 people in the Chicago area alone. Studies based on these types of statistics estimate that in Atlanta, for example, even a warming of about two degrees (F) would increase heat-related deaths from 78 today to anywhere from 96 to 247 people per year. If people are able to install air conditioning and otherwise acclimatize themselves to the hotter temperatures, the lower estimate is more likely.
Warmer temperatures may decrease the number of people who die each year from cold weather. However, in the United States, only 1000 people die from the cold each year, while twice that many die from the heat. Moreover, of the ten states with the greatest number of cold-related deaths, Alaska and Illinois are the only northern states. For the most part, cold-related deaths occur during occasional cold spells in areas with mild winters where people prepare less for the cold, or during freak events like the severe snow storm that struck Colorado in November of 1997. Global warming is unlikely to reduce either of these situations. Finally, deaths due to the heat are more sensitive to temperature changes than deaths due to the cold; the difference between -20°F and -15°F, for example, has a much smaller impact than an increase from 95°F to 100°F.
Global warming may also increase the risk of some infectious diseases, particularly those diseases that only appear in warm areas. Diseases that are spread by mosquitoes and other insects could become more prevalent if warmer temperatures enabled those insects to become established farther north; such "vector-borne" diseases include malaria, dengue fever, yellow fever, and encephalitis. Some scientists believe that algal blooms could occur more frequently as temperatures warm--particularly in areas with polluted waters--in which case diseases such a cholera that tend to accompany algal blooms could become more frequent.
In spite of these risks, increased mortality is not an inevitable consequence of global warming. Malaria, for example, is rare in the United States even in warmer regions where the mosquito that transmits the disease is found, because this nation has the ability to rapidly identify and contain outbreaks when they appear. Heat-related deaths can be prevented by emergency measures to move vulnerable people to air-conditioned buildings, and by reducing the emissions of photochemical oxidants which cause ground-level ozone. Many of the impacts of climate change on health could be avoided through the maintenance of strong public health programs to monitor, quarantine, and treat the spread of infectious diseases and respond to other health emergencies as they occur. Although air-conditioning and public health programs may impose additional costs on the public and private sectors, they would often be preferable to the impacts on human health that would otherwise occur.
Global warming could have many impacts on fish and other aquatic species. Some bodies of water may become too warm for the fish that currently inhabit those areas; but warmer temperatures may also enable fish in cold ocean waters to grow more rapidly. Global warming may also change the chemical composition of the water that fish inhabit: the amount of oxygen in the water may decline, while pollution and salinity levels may increase. Loss of wetlands could diminish habitat and alter the availability of food for some fish species. Scientists have examined the implications for three types of fisheries: (1) inland freshwater fisheries found in non-tidal rivers, lakes, and streams; (2) coastal fisheries, which extend from tidal freshwater rivers, to estuaries, to coastal ocean fisheries; and (3) deep ocean fisheries.
Higher water temperatures may have the most important implications for inland fisheries. Like plants and birds, most species of fish tolerate--and many require--winter cooling and summer warming by tens of degrees.
Wetland loss, salinity changes, and higher temperatures are all likely to affect finfish and shellfish in the coastal zone. The most vulnerable species are those that either reproduce in coastal wetlands, spend their entire lifetimes in an estuary, or both.
Scientists generally expect fish on the high seas to be less affected by global warming than coastal and inland fisheries.
Relatively little research has been conducted on the possible impact of climate change on deserts. Scientists have focused on a different question: Are deserts likely to expand?
Scientists at NASA have suggested that in the long run, a worldwide expansion of deserts is likely (Rind et al. 1990). Today, deserts tend to be found at latitudes between 20 and 32 degrees. Soils are extremely dry at these latitudes because the potential for evaporation and transpiration is generally greater than the average rainfall. If global temperatures were to rise by 4°C, the potential evapotranspiration (see glossary) would increase 30-40 percent, while precipitation would only increase 10-15 percent. As a result, the area with a deficiency of precipitation would expand poleward and toward the equator.
Studies that focus on what is likely to occur over the next century, however, do not indicate whether deserts are more likely to expand or contract. Studies using the biogeographic models have estimated that desert shrublands could increase by as much as 185 percent or decrease by as much as 56 percent.
Changing climate is expected to increase both evaporation and precipitation in most areas of the United States. In those areas where evaporation increases more than precipitation, soil will become drier, lake levels will drop, and rivers will carry less water.
Lower river flows and lower lake levels could impair navigation, hydroelectric power generation, and water quality, and reduce the supplies of water available for agricultural, residential, and industrial uses. Some areas may experience both increased flooding during winter and spring, as well as lower supplies during summer. In California's Central Valley, for example, melting snow provides much of the summer water supply; warmer temperatures would cause the snow to melt earlier and thus reduce summer supplies even if rainfall increased during the spring. More generally, the tendency for rainfall (see climate system trends) to be more concentrated in large storms as temperatures rise would tend to increase river flooding, without increasing the amount of water available.
Many federal and state agencies are actively engaged in reducing the nation's vulnerability to these types of impacts. In the western United States, where freshwater is scarce, a gradual trend toward allowing farmers to sell water is enabling scarce water to be used more efficiently. Along the Mississippi River and other floodplains, the Federal Emergency Management Agency and others are reviewing structural and land-use measures for reducing vulnerability to floods. Finally, both the Corps of Engineers and the Bureau of Reclamation are developing better ways to manage the federal system of reservoirs in the face of changing mate to meet the competing needs of navigation, hydropower, water supply, recreation, and environmental quality.
Climate change could impair navigation by changing average water levels in rivers and lakes, increasing the frequency of both floods during which navigation is hazardous and droughts during which passage is difficult, and necessitating changes in navigational infrastructure. On the other hand, warmer temperatures could extend the ice-free season.
Changes in the flows of rivers would have a direct impact on the amount of hydropower generated, because hydropower production decreases with lower flows. Because of the ambiguous projections of changes in future river flow, studies of the impacts of climate change show ambiguous effects on hydropower production.
In some parts of the western United States, the most widely discussed potential impact of climate change is the impact on water supply and demand. The potential changes in water supplies would result directly from the changes in runoff and the levels of rivers, lakes, and aquifers.
Decreased river flows and higher temperatures could harm the water quality of the nation's rivers, bays, and lakes. In areas where river flows decrease, pollution concentrations will rise because there will be less water to dilute the pollutants. Increased frequency of severe rainstorms could increase the amount of chemicals that run off from farms, lawns, and streets into the nations rivers, lakes, and bays.
Although the impacts of sea level rise and associated coastal flooding have been more widely discussed, global climate change could also change the frequency and severity of inland flooding, particularly along rivers.
We Can Curb the Global Warming Threat
The good news is that we can slow and eventually stop global warming, but we must act today. The most important step we can take to curb global warming is to improve our nation's energy efficiency. Our cars and light trucks, home appliances and power plants could be made much more efficient by simply installing the best current technology. Energy efficiency is the cleanest, safest, most economical way we can begin to deal with global warming.
No global warming solution will succeed unless we can control emissions from cars. More carbon dioxide pollution comes from America's cars and trucks than from the entire nation of Japan. If we are to make any progress in slowing global warming, we must make our cars go further on a gallon of gas.
While there is no technology to remove C02 from a car's exhaust, we can make them pollute less by making them more fuel efficient. By using today's best technology, car makers could dramatically increase the fuel economy of cars and trucks. In fact, vehicles such as the 1994 Honda Civic VX have shown that with only minor changes today's cars could get over 50 miles per gallon.
Clean up our electrical power plants. We also need to clean up our electrical power plants. Most electric utilities still use coal to produce electricity, spewing millions of tons of carbon dioxide and other pollution into the atmosphere every year. Part of the problem could be solved by converting these plants to burn cleaner natural gas.
We could do much more to save energy in our homes and office buildings. More energy efficient lighting, heating and air-conditioning could keep millions of tons of carbon dioxide out of our air each year.
Step up the use of clean wind and solar energy. Harnessing the clean, abundant energy of the sun and wind is critical to solving the global warming problem. Technological advances have brought the cost of electricity generated by the wind down by 85% since 1981. Solar energy tCechnology has made remarkable progress as new photovoltaic cells have been developed to convert ever greater amounts of sunlight directly into electricity. Today the costs of wind and solar power are approaching that of
dirty coal-fired plants.
Midwestern states in particular hold enormous potential as sources of renewable energy. Renewable sources currently make up less than 1% of the energy market in the US. States like Kansas, Nebraska, North Dakota, and South Dakota hold the potential of becoming the Saudi Arabia of wind power.
AMERICA MUST INVEST IN THE FUTURE
The United states is now entering the 21st century relying on dirty, polluting 19th century fossil fuel technology. It is good for America's environment, economy, health, and climate to use energy more efficiently to develop clean alternative sources of electricity, and to use more efficient methods of transportation. We must begin to look towards a cleaner, healthier future.
Today, action is occurring at every level to reduce, to avoid, and to better understand the risks associated with climate change. Many cities and states across the country have prepared greenhouse gas inventories; and many are actively pursuing programs and policies that will result in greenhouse gas emission reductions.
At the national level, the U.S. Global Change Research Program (USGCRP) coordinates the world's most extensive research effort on climate change. In addition, the Clinton Administration is actively engaging the private sector, states, and localities in partnerships based on a win-win philosophy and aimed at addressing the challenge of global warming while, at the same time, strengthening the economy.
At the global level, countries around the world have expressed a firm commitment to strengthening international responses to the risks of climate change. The U.S. is working to strengthen international action and broaden participation under the auspices of the Framework Convention and in light of the Third Conference of the Parties to the Framework Convention on Climate Change that will take place in Kyoto, Japan this year.
GLOBAL ACTIONS
The U.S. believes that climate change is a global problem that must be addressed by the global community. The U.S. is committed to strengthening international responses to the risks of climate change. The U.S. is working to strengthen international action and broaden participation under the auspices of the Framework Convention.
Through the U.S. Initiative on Joint Implementation, American businesses are encouraged to pursue joint partnership projects abroad that reduce emissions and also help disseminate clean technology. In addition, the U.S. Countries Studies Program, as well as other targeted initiatives, are building capacity for appropriate cost-effective actions in some 50 developing and transition countries.
The IPCC was established jointly by the United Nations Environment Programme and the World Meteorological Organization in 1988. The purpose of the IPCC is to assess information in the scientific and technical literature related to all significant components of the issue of climate change. The IPCC draws upon hundreds of the world's expert scientists as authors and thousands as expert reviewers.
Leading experts on climate change and environmental, social, and economic sciences from some 60 nations have helped the IPCC prepare periodic assessments of the scientific underpinnings for understanding global climate change and its consequences. With its capacity for reporting on climate change, its consequences, and the viability of adaptation and mitigation measures, the IPCC is also looked to as the official advisory body to the world's governments on the state of the science of the climate change issue.