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close this bookClimate Protection and the National Interest (WRI, 1997, 56 pages)
close this folder2. THE CLIMATE CHANGE PROBLEM
View the document(introduction...)
View the documentThe Cooling Effect of Air Pollution
View the documentSearching for the Signal of Global Warming
View the documentExpected Impacts of Global Warming
View the documentCoping with Climate Change


There is no doubt that Earth has a natural greenhouse effect. Without it, the world would be about 33°C (60°F) colder. Life as we know it would not be possible. The great French physicist Jean Fourier argued 170 years ago that Earth's atmosphere acts like the glass of a greenhouse by admitting the sun's light while impeding the escape of the earth's radiant heat (infrared radiation) back into space.


The buildup of carbon dioxide accounts for about two-thirds of the human sources of excess greenhouse warming from long-lived gases.5 (Figure 1 shows the history of global CO2 emissions.) Each year, the burning of fossil fuels and biomass, along with other activities such as cement making, releases over seven billion metric tons of carbon to the atmosphere in the form of CO2, raising the atmospheric concentration of the gas by about half a percent annually. Figure 2 shows CO2 emissions for the United States for the period 1980 to 1996 while Figure 3 shows the source of emissions for 1994 by sector and fuel. Note that electric-power production and transportation are by far the largest and fastest-growing sources. With current global emissions of some 6.3 billion metric tons per year (1995), fossil fuel combustion is the best quantified and the largest source of CO2 from human activity. Since preindustrial times, the global CO2 concentration has increased almost 30 percent, from 280 parts per million (ppm) to about 360 ppm today. (See Figure 4.) Carbon dioxide stays in the atmosphere 50 to 200 years.6

In 1896 - after performing at least 10,000 hand calculations - the Nobel-prize winning Swedish chemist Svante Arrhenius correctly reasoned that the quantities of water vapor and carbon dioxide (CO2) in the atmosphere absorb enough of the earth's outgoing heat radiation to warm the earth by nearly 33°C (60°F). Arrhenius concluded that a doubling of atmospheric CO2 would raise average global temperatures by 5 to 6°C (9 to 11°F) over the preindustrial temperature3 This is remarkably close to the range of 1.5 to 4.5°C (2.7 to 8.1°F) that climate experts now believe would accompany a doubling of atmospheric CO24.


Methane (the main component of natural gas) has both natural and human sources. Natural sources include peat bogs, termites, swamps, and other wetlands. Human sources include rice paddies, domestic animals, landfills, biomass burning, and the production and burning of fossil fuels. Fossil fuels account for about 20 percent of the total, including leakage from natural gas pipelines, oil wells, and coal seams.7 About 60 to 80 percent of all methane emissions are of human origin. Atmospheric methane concentrations have been increasing in the atmosphere at about 0.6 percent per year8 and have more than doubled from preindustrial levels. Methane stays in the atmosphere 12 to 17 years and accounts for about 20 percent of greenhouse warming from human sources.

Over the past century, human agricultural and industrial activities have led to the buildup of CO2 and other greenhouse gases, including methane, nitrous oxide, ozone, and the halogenated compounds (including the CFCs). These gases are trapping yet more of the earth's outgoing radiation, leading to an enhanced greenhouse effect and, eventually, to a warmer earth. (See the sidebars on pages 5 - 7 for a discussion of the sources, properties, and emission trends of the important greenhouse gases.)

The Cooling Effect of Air Pollution

In addition to the CFC destruction of ozone (see the sidebar on halogenated compounds), a second cooling effect offsets some global warming. Small atmospheric particles (called aerosols) are formed from sulfur dioxide air pollution, biomass burning, and other sources. These aerosols shield the earth - mostly in regions down-wind of industrialized areas - from some of the incoming sunlight and cause cooling both directly, by scattering sunlight, and indirectly, by helping to form reflective clouds13. According to the Intergovernmental Panel on Climate Change (IPCC), these small particles have offset some of the expected global warming over the past several decades. The predicted warming, with and without the aerosol effect, is shown in Figure 5. The cooling effect of the aerosols brings the calculated rise in temperature into closer agreement with the observed changes of the past few decades. Unlike most greenhouse gases, aerosols remain in the air for only a matter of days. As a result, as pollution emissions are reduced, so too will the cooling effect of the aerosols. Given the continued need to cut air pollution emissions to protect health and reduce acid deposition, the task of cutting greenhouse gas emissions becomes increasingly important.



The principal sources of nitrous oxide from human activities are the application of nitrogen fertilizers to agricultural lands, the burning of biomass and fuels, and industrial chemical production. Human sources are about a third of total global emissions. Nitrous oxide is a very stable molecule (lifetime of 120 years) and also contributes to stratospheric ozone depletion.9 This gas accounts for about 5 percent of the human sources of greenhouse warming.

BOX 1 - THE 12 HOTTEST YEARS IN RECORDED HISTORY ( in descending order )

1995,1990,1991,1981,1996, 1988, 1987,1994,1983, 1980, 1989, 1993

Source: Goddard Institute for Space Studies, NASA.


Halogenated compounds contain fluorine, chlorine, bromine, or iodine, and many such compounds are strong greenhouse gases. Halocarbons containing carbon and either chlorine or bromine, such as the CFCs, halons, and HCFCs, also cause stratospheric ozone depletion. CFCs are made for use as aerosol propellants, blowing agents for plastic foams, refrigerants, and solvents. They are particularly damaging as greenhouse gases because of their long lives in the atmosphere and their effectiveness in trapping heat, approximately 20,000-30,000 times that of CO2. Hydrofluorocarbons (HFCs) - substitutes for some CFC applications - are also potent greenhouse gases.

Estimates of the net warming effect of CFCs have recently been reduced. This reduction stems from the cooling effect from the CFC destruction of ozone (a greenhouse gas) in the lower stratosphere.11 CFCs and some other ozone-depleting compounds have been phased out in the industrialized countries by the Montreal Protocol on Substances that Deplete the Ozone Layer but production for essential uses and to meet developing-country needs continues.

Also included in the halo-carbon family are perfluorocarbons (PFCs) and sulfur hexafluoride (SF6), which have lifetimes measured in thousands of years. PFCs are a byproduct of aluminum making and are also manufactured for use in the semiconductor industry. They are exceedingly powerful greenhouse gases. Though presently low, concentrations of the PFCs and SF6 are increasing. Because of their long lifetimes, these compounds represent an essentially irreversible threat to the climate.12 The halocarbons contribute about 10 percent of the warming from human sources.



The problem of climate change is being addressed internationally through the UN Framework Convention on Climate Change (UNFCCC). Important milestones include


166 governments endorse the UNFCCC at the Earth Summit in Rio de Janeiro. The United States ratifies the treaty on October 15, 1992.


By November, 50 nations have ratified the treaty.


UNFCCC enters into force in March.


First meeting of the Conference of the Parties (COP1), in Berlin. "Berlin Mandate" adopted to guide negotiations of a protocol requiring further action for post-2000.


At COP2, in Geneva, United States takes strong position in favor of binding targets and timetables for reducing emissions.


COP3 in Kyoto in December. The goal is to adopt a protocol that will required reductions in greenhouse gas emissions after the year 2000.


Ozone (O3) in the upper atmosphere (stratosphere) acts as a crucial filter that protects life on the planet from many of the harmful effects of ultraviolet radiation. However, ozone in the lower atmosphere (troposphere) is both a greenhouse gas and, in many polluted urban areas, a threat to public health. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are both necessary for ozone formation. VOCs and NOx have both natural as well as man-made sources, but in urban areas, which are prone to ozone formation, combustion is a major source of both.10 As NOx are formed, they combine with VOCs in the presence of sunlight to form tropospheric ozone. Background tropospheric ozone concentrations, the evidence suggests, have approximately doubled in the northern hemisphere since preindustrial times.

Searching for the Signal of Global Warming

Global surface-temperature data indicate that over the past century the earth has warmed by about 1°F (about 0.5°C). Although there is no doubt that greenhouse gases are building up in the atmosphere, there is less certainty about whether the bulk of the observed warming over the past century is a direct result of this buildup or partly die result of a natural fluctuation. Much of the warming has occurred recently: 1995 was the hottest year in the past century, and the next 11 hottest years have all occurred since 1980. (See Box 1.) According to the 1995 IPCC assessment, "the observed warming trend is unlikely to be entirely natural in origin," and "the balance of evidence suggests that there is a discernible human influence on global climate."

Global surface-temperature data indicate that over the past century Earth has warmed by about 1°F. Much of the warming has occurred recently: 1995 was the hottest year in the past century and the next 11 hottest years have all occurred since 1980.


Although the basic principles of enhanced greenhouse warming are scientifically well established, there are still significant uncertainties about the size of regional changes, when they will appear, and what their consequences will be. Climatologists study climate change using complex computer models. When incorporated into these models, the two cooling effects just described - the CFC-ozone connection and the pollution-aerosol effect - go a long way toward explaining why the observed warming over the past few decades is lower than climatologists had predicted based solely on the buildup of greenhouse gases.

The threat of climate change is being addressed through the United Nations Framework Convention on Climate Change, which was adopted at the Earth Summit in 1992. Countries worldwide will meet in December 1997 in Kyoto with the goal of adopting a protocol to reduce greenhouse gas emissions. Important milestones in the treaty process are listed in Box 2.

Many recent studies provide supporting evidence for the IPCC's 1995 conclusion that human-induced warming of the earth is probably occurring. Combining data on droughts, above-normal precipitation in the winter months, drenching rainstorms, and other weather extremes, Thomas Karl and his colleagues at the National Climatic Data Center in Asheville, North Carolina, constructed a Greenhouse Climate Response Index for the United States. Since 1980, the index has been elevated, indicating an above-average number of extreme events. Karl and his colleagues believe there is only a 5 to 10 percent chance that this is a natural fluctuation.14 According to Karl, the trends are indeed those projected for an intensified greenhouse.15 In a warmer world, he says, there will be more precipitation, and it will be more likely to come in more extreme events.16


The conclusion that the observed warming trend is not simply a natural fluctuation is affirmed by research at several institutions. Basing their conclusions on climate model calculations, scientists at the Max Planck Institute for Meteorology in Hamburg, Germany, concluded that the warming of the earth over the past 30 years goes far beyond natural variations, indeed has only one chance in 40 of being natural.17


Several other elements of a "global warming fingerprint" have been observed. Primarily as a result of ocean warming and the melting of glaciers, sea levels are rising slightly more than 2 mm per year (about 1/16 of an inch). They have already risen by 10 to 25 cm (4 to 10 inches) over the past century18. Climate change, including sea-level rise and a more intense hydrological cycle, will increase the vulnerability of some coastal populations to flooding and erosional land loss.19 Already, some 46 million people are at risk of flooding due to storm surges.


Sea ice around Antarctica is melting, and the Arctic ice pack has been shrinking faster during the past two decades.20 Studies by Norwegian scientists show that Antarctic sea ice is declining by 1.4 percent per decade21. The temperature at the South Pole has increased by 2.5°C (4.5°F) over the past 50 years.22 At the North Pole, sea-ice melting has accelerated from 2.5 percent per decade to 4.3 percent.23

Glaciers continue to retreat. According to recent work at the University of Colorado's Institute of Arctic and Alpine Research, the world's total glacier mass has diminished by about 12 percent over the past 100 years as a result of higher temperatures.24 A separate Russian study also shows that the volume of small glaciers has decreased. Australian scientists have reported that the equatorial glaciers on the summit of Mt. Jaya in Indonesia are disappearing rapidly, most likely from Earth's warming.

Expected Impacts of Global Warming

Because CO2 and other greenhouse gases are so long-lived in the atmosphere, enhanced greenhouse warming can be expected to persist for centuries. The impacts - many of which are effectively irreversible25 - will affect everyone on earth. Human health, patterns and intensity of precipitation, water and food supplies, coastal development, energy supplies, the viability of natural systems: all will be affected if Earth's climate continues to change.

Several kinds of health impacts from higher temperatures have been identified, both direct and indirect. The long term will see the predominance of indirect effects, including the spread of vector-borne infectious diseases.26 Several such diseases, including malaria, dengue, and viral encephalitides, are particularly sensitive to changes in climate. The symptoms of dengue, a disease spread by mosquitos, include fever, pain. Its severe form causes widespread hemorrhaging. The disease is spreading north through Mexico and has been recently detected in Texas. In the past 20 years there has been a dramatic increase in dengue and dengue hemorrhagic fever worldwide with 50 to 100 million cases of dengue a year, and several hundred thousand cases in its severe hemorrhagic form. Two species of mosquito capable of spreading the disease have already entered the United States and fanned out across the lower Southeast.

The 1993 outbreak in the Southwestern United States of hantavirus pulmonary syndrome, a sudden respiratory disease, killed 53 percent of the people it struck. It provides a dramatic example of how a subtle climate change, even a temporary one, can promote disease27. The outbreak was traced to a 10-fold increase in the population of deer mice that carry the virus. This increase resulted from six years of drought (which reduced the population of mouse predators) followed by heavy rains in the spring of 1993 (and an abundance of food for the mice). The mice shed the virus in their urine, and contaminated dust spread the disease widely

The 1993 outbreak of hantavirus pulmonary syndrome - a sudden respiratory disease that killed 53 percent of the people it struck - provides a dramatic example of how a subtle climate change, even a temporary one, can promote disease.

More directly, the frequency of heat-related illness and death is expected to increase. Extreme heat waves can bring on heart attacks, strokes, or other fatal ailments in people at risk. Using models that estimate climate change for the year 2020 and 2050, researchers estimate that summer mortality will increase dramatically and winter mortality will decrease slightly.28 (Researchers estimate that perhaps 40 percent of those dying from heat waves would have died soon regardless of the weather.) Other direct health effects include deaths and injury from more extreme weather events (floods, storms, winds).29 Additional warming in urban areas would accelerate the formation of air pollutants such as smog (largely ozone), with negative consequences for human health. In sum, a sizable net increase in weather-related human mortality is expected if the climate warms as the models predict.30

Changing precipitation patterns can also lead to major social upheaval. The disastrous 1996 - 97 winter and spring floods in various regions of the United States illustrate what could lie ahead. The National Oceanic and Atmospheric Administration (NOAA) expects extreme flooding like the December 1996-January 1997 floods in the Northwest to become more frequent across the country due to an increase in precipitation extremes caused by climate change.31 These storms led to 30 deaths, to the evacuation of more than half a million people, and to property losses exceeding several billion dollars (including $1.8 billion in California, $500 million in Nevada, and $125 million of insured losses in Washington state).

A continued warming of the earth will lead to other impacts. Sea-level rise will threaten cities and countries worldwide. The IPCC's best estimate of sea level rise from 1990 to 2100 is about 49 cm (19 inches).32 Ocean levels would continue to rise long after the year 2100, however, until the oceans reach thermal equilibrium. Continued sea-level rise would erode barrier islands and virtually eliminate some island chains, such as the island nation of Maldives in the Indian Ocean. Higher seas would inundate the productive coastal wetlands and estuaries upon which marine fisheries and wildlife resources depend; drive millions of people around the world from their homes; cause saltwater intrusion into coastal groundwater supplies; adversely affect nearby infrastructure such as highways, power plants, sewage treatment plants, beaches, and cultural and historical sites; and increase the severity of storm damage to lagoons, estuaries, and coral reefs.

Highly productive agricultural areas such as the deltas of the Nile, Ganges, Yangtze, and Mekong rivers would be seriously affected by sea-level rise, forcing millions of people to move inland. Continued warming would also lead to shifts in rainfall patterns as global precipitation increases, leading to changes in availability of water for irrigation, hydropower, and navigation. Unable to migrate fast enough to keep up with the changing climate, whole ecosystems would be lost.

Scientists expect impacts on agriculture to be mixed. Their models suggest that if carbon dioxide levels double, agricultural production could be maintained at projected baseline rates, though regional effects would vary widely.33 Still, uncertainties are great and many factors have not been examined for their impacts. The IPCC cautions that the model calculations supporting its conclusions take into account the fertilization effects of CO2 but "do not include changes in insects, weeds, and diseases; direct effects of climate change on livestock; changes in soil and soil-management practices; and changes in water supply caused by alterations in river flows and irrigation." Failure to integrate many key factors into climate models limits the ability of researchers to consider scenarios in which the climate is still changing and to fully address the costs and potential of adaptation.34

Because tropical storms such as hurricanes derive their energy from the oceans, it is possible that as the seas warm, there could be an increase in the number and intensity of such storms. A recent statistical analysis by scientists at the University College London concludes that the record warming of the Atlantic Ocean may have been the primary cause of the exceptional 1995 hurricane season which saw twice the usual number of hurricanes.35 While the years 1995 and 1996 were the two busiest consecutive hurricane seasons on record, and 1997 is also predicted to be above average (six hurricanes are predicted of which two are expected to be intense),36 a three-year period is too short to establish a trend. A natural cycle of increased hurricane activity similar to what occurred in the 1940-1960 period may be starting.


If the number of powerful hurricanes - of natural origin or the result of global warming - does increase, damages could be severe, the result of more people living in more expensive homes in vulnerable coastal regions. It is estimated that a class-5 hurricane striking the northeast United States coastal corridor from Delaware to Connecticut could cause over $50 billion in insured losses (perhaps twice that amount in total losses).37 The prognosis, according to the National Center for Atmospheric Research, is for an increased likelihood of such major storms: "it is only a matter of time before the nation experiences a $50 billion or greater storm, with multi billion-dollar losses becoming increasingly frequent. Climate fluctuations which return the Atlantic basin to a period of more frequent storms will enhance the chances that this time occurs sooner, rather than later."38 The possibility of devastating property losses has spurred the insurance industry to a growing interest in climate change and in options to reduce their vulnerability to these potentially financially disastrous storms.

Coping with Climate Change

Global warming is one of the most important environmental risks affecting long-range planning, particularly in the energy sector. Figure 6 shows several possible "pathways" to various stabilized CO2 concentrations: 450, 550, and 650 parts per million (ppm), respectively. Major reductions would be needed in CO2 emissions to reach any of these goals. According to the IPCC, stabilizing atmospheric CO2 concentrations at twice preindustrial levels (that is, at about 550 ppm) would require eventual reduction of global carbon emissions by at least 60 percent of today's levels. There is no guarantee whatever that a doubling of CO2 concentration in the atmosphere would be a "safe" concentration.