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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

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.