HTML _ Global Climate Change
8-Mar-2001

Abstract: It is now widely accepted by the scientific community that human activities, such as the burning of fossil fuels, deforestation, and certain land-use practices, are increasing atmospheric concentrations of carbon dioxide (CO2), which, along with increasing concentrations of other trace gases (methane, nitrous oxide, hydrofluorocarbons-HFCs, perfluorinated compounds-PFCs, sulfur hexafluoride-SF6, and trifluoromethyl sulfur pentafluoride-SF5CF3), could affect global climate. Careful monitoring and direct measurement of the concentrations of those gases in the atmosphere, and analysis of ice cores in Greenland and Antarctica that have captured past concentrations of some of those gases, leave no doubt that their global concentrations are increasing. Emissions of CO2 and the other greenhouse gases are not regarded as criteria pollutants (e.g., carbon monoxide, nitrogen oxides, volatile organic compounds, ozone, particulate matter) in terms of direct effects on human health and, therefore, have not been regulated directly in such pollution control laws as the Clean Air Act. In addition, they are emitted by most major productive activities in human societies -- transportation, use of power to heat and cool buildings, industrial activity, etc. Their pervasive nature makes limitations seem potentially restrictive in all these areas. Any specific emissions limits are shaping up to be very controversial.

According to recent projections based on computer models of the atmosphere, if these gases continue to accumulate, a globally averaged warming of 2.7 to 10.8 degrees F could occur over the next 100 years through enhancement of Earth's naturally occurring ¨greenhouse effect¨ -- the process by which the atmosphere traps infrared radiation emitted by the Earth, warming the Earth's surface in a process somewhat analogous to that which occurs in a greenhouse. The potential for impacts of such a climate change -- some positive, some negative -- on natural systems, national economies, and quality of life is uncertain and the subject of intense investigation. Thus far, scientific evidence suggests that, in some regions of the world, climate change could be detrimental for human health, ecosystems, food security, and water resources.

Globally averaged air temperatures at the Earth's surface have warmed by about 0.9 degrees F over the last 100 years. Natural variability of climate is large enough, however, that even the record-setting warmth of some years in the 1980s and 1990s or singular events such as a severe summer drought or seasonal flooding have not allowed a majority of scientists to state with any certainty that a global warming signal attributable to human activities has been identified . . . at least not until now. The Intergovernmental Panel on Climate Change (IPCC), jointly established in 1988 by the United Nations World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP), reported in its Second Assessment (1996) that ¨. . . [such] a change is unlikely to be entirely natural in origin . . . [and that] the balance of evidence, from changes in global mean surface air temperature and from changes in geographical, seasonal, and vertical patterns of atmospheric temperature, suggests a discernible human influence on global climate.¨ And now, the latest report (January 2001), the Intergovernmental Panel's Third Assessment, concedes that a firmer association between human activities and climate seems to have emerged. That is news, because reservations about the source of the past century's warming and whether it bore a human fingerprint are often cited in policy debates, usually in support of deferring actions aimed at mitigating possible global warming. In addition, the IPCC reports a higher range of potential warming - roughly between 3 and 11 degrees Fahrenheit over the next 100 years. [read report]

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