Mothball the polar fleece and break out the T-shirts. Far into the future, the earth is likely to keep getting warmer and warmer as ice caps melt and sea levels rise.
That's the essence of the latest scientific data on global warming, reported this week by the United Nations Intergovernmental Panel on Climate Change. The work of several hundred scientists, who spent three years on the project, the 1,000-plus-page report is filled with complex formulas and intricate data.
But the bottom line is clear and unambiguous: "Anthropogenic [human-caused] climate change will persist for many centuries." What's more, global temperatures could rise by more than 10 degrees Fahrenheit over the next century - as much as they've risen since the last Ice Age 20,000 years ago. That's nearly twice the increase the UN last estimated, in 1995.
While 10 degrees seems barely the difference between one or two layers of thermal underwear on a frosty New England morning, that much warming could bring with it more droughts, thunderstorms, floods in low-lying areas, and water-borne diseases.
Ever since "global warming" entered the political lexicon about a decade ago, questions of whether it exists and what to do about it have been hotly debated. This latest news from the IPCC, billed as the most comprehensive evidence of long-term climate change, is no exception.
Skeptics have already expressed doubts about the report's credibility. Myron Ebell, director of environmental policy at the Washington-based Competitive Enterprise Institute, claims the "scary predictions" are based on discredited computer models.
The report's draft summary, issued by scientists and UN officials meeting in Shanghai this week, "has everything to do with political spin and very little to do with climate science," says Mr. Ebell.
That seems to be a minority view, however. Most experts now acknowledge that the "greenhouse effect" is the cause of perceptible climate change, and that its main source is the carbon dioxide and other heat-trapping gases spewed from factories, furnaces, autos, and other fossil-fueled sources that have mushroomed since the Industrial Revolution.
One reason for this is that scientists have increasing confidence in the ability of computer models to project future climate. The IPCC report, for example, now says that it is "very likely" that this century will experience "higher maximum temperatures and more hot days over nearly all land areas."
This would be a continuation of recent trends. The 1990s was the warmest decade, and 1998 was the warmest year, since instrument recording started in 1861. Snow cover at higher elevations in the Northern Hemisphere has decreased by 10 percent since the 1960s, according to the report, and the thickness of Arctic ice has declined by as much as 40 percent.
While some skeptics say recent global temperature increases are a part of natural cycles, the UN report's authors assert - more firmly than they have in the past - that the main cause is human civilization. Concentration of CO2 in the atmosphere has increased 31 percent over the past 250 years, to a level that has not been exceeded in the past 420,000 years, "and likely not during the past 20 million years."
Until fairly recently, most major industrial fossil-fuel producers and users resisted the notion of global warming and especially what they saw as the dire remedies proposed by environmentalists. But many - including major oil companies and auto-makers - now acknowledge the reality of climate change and are working to reduce their greenhouse-gas emissions.
The US Department of Energy reported last week that in 1999, 201 American companies had undertaken 1,715 voluntary projects that resulted in a total reduction of 226 million metric tons of carbon dioxide and other greenhouse substances - three times as much as in 1994 when the Energy Department's program began. Electric-power producers and waste-treatment facilities accounted for most of that. Still, that reduction represents just 3.4 percent of total US greenhouse gas emissions in 1999.
But what's the solution?
How to get more substantial reductions is one of today's thorniest international issues. In Kyoto, Japan, in 1997, more than 100 countries signed a treaty that included the general requirement that industrialized nations reduce greenhouse-gas emissions 5 percent below 1990 levels by 2010. How to do that has never been settled, however, and the "Kyoto Protocol" has yet to be ratified by any industrialized nation.
Critics (including President George W. Bush) say any agreement must include developing countries as well. Mr. Bush, who worked in the oil industry, generally favors an approach to such issues that is based on more voluntary compliance and a reliance on the market.
In any case, this week's UN report is likely to accelerate efforts to control climate change.
"Although this problem was created inadvertently, its consequences are now quite clear," says Nancy Kete, director of the World Resources Institute's climate, energy, and pollution program. "The responsibility to reduce carbon emissions - either through energy conservation or new, low-carbon energy sources - lies with industrialized countries."
(c) Copyright 2001. The Christian Science Publishing Society