The odds are dead even that the world's average temperature will increase at least 5 degrees by the end of the century, enough to trigger flooding, famine and drought across much of the globe, according to a new study.
It's the first time scientists have computed the likelihood that Earth would get warmer by specific degrees. The study addresses a key criticism about the issue of global warming, that of scientific uncertainty, which the Bush administration has cited for its go-slow approach to the issue.
The study, in today's issue of the journal Science, is done by Tom Wigley, a senior scientist at the U.S. National Center for Atmospheric Research in Boulder, Colo., and Sarah Raper of the University of East Anglia in England. Their findings were published as world leaders meet in Germany to work on a controversial 1997 Kyoto treaty to fight global warming.
Their study concluded that there is a 90 percent chance global warming will increase Earth's temperature 3 to 9 degrees by 2100. Wigley and Raper consider a 5-degree increase most likely.
Scientists are beginning to use these probability studies to try to understand what global warming might mean in the future.
The 5-degree increase by 2100 crosses a key threshold for climate scientists. That would make it hot enough to cause more tropical diseases, droughts, floods, heat waves and severe weather in general.
Effects for the United States would be milder than for countries that already have tropical or semi-tropical climates.