Degrees of Uncertainty in Climate Studies
One Study Says Surge in Global Warming Likely; Another Highlights Unknowns
_____Special Report_____
By Eric Pianin
Washington Post Staff Writer
Friday, July 20, 2001; Page A16
As President Bush and other U.S. officials air their differences this week with European allies over global warming, a study released yesterday concludes there is a high probability the Earth's average temperature will rise between 4 and 7 degrees Fahrenheit over the coming century.
The warming predicted in the study by a U.S. and a British scientist is five times the 1 degree rise that has been observed over the past century.
The estimate of relatively fast-rising temperatures is well within the range predicted early this year in a report by the United Nations' Intergovernmental Panel on Climate Change.
The U.N. panel of hundreds of international scientists concluded that Earth's average temperature was likely to rise between 2.5 and 10.4 degrees Fahrenheit in the coming century, up significantly from the panel's 1995 estimate of 1.4 degrees.
The panel's findings have been the basis of international debate over global warming.
The latest study, prepared by Tom Wigley of the National Center for Atmospheric Research and Sarah Raper of the University of East Anglia in England, found a 9-in-10 chance that the global average temperature will rise 3 to 9 degrees in the coming century, with a 4- to 7-degree increase most likely.
The study, appearing in today's issue of the journal Science, sought to interpret the likelihood of the new estimates, taking into account the wide uncertainties about future human activities and the climate's response to them.
The researchers identified the main sources of uncertainty and estimated the probability of their values falling within defined ranges. They then used these results to drive a simplified computer climate model and combined the various model results into probability ranges for temperature increases.
"We are assigning probabilities to long-term projections to aid policymakers in assessing the risks that might accompany various courses of action or nonaction," Wigley said. "If all scenarios are believed to be equally likely, it's difficult to plan."
Another study published in Science, however, cautions that future emissions of greenhouse gases and their resulting environmental and economic consequences "are subject to large uncertainties."
The study by scientists specializing in global change at the Massachusetts Institute of Technology and the University of North Carolina challenged the U.N. panel's forecast of rising temperatures over the coming century.
"This finding is not accompanied by any quantification of the probability of those projections or the probability bounded by this range, and the reader is left to guess whether the likelihood of exceeding this range is 1 in 10 or 1 in 1,000," the report said.
Absent a clear picture of where the Earth's average temperature is headed, the study concluded, "policy discussion threatens to deteriorate into a shouting match, where analysis results are used both to support calls for urgent action and to justify doing nothing."
Bush has acknowledged that climate change is a serious problem but also has said that substantial doubts remain about the causes and the severity of global warming.
Yesterday, the president vowed to stand firm against the global warming treaty supported by European allies as he opened his second trip to Europe.
British, French and German leaders reportedly will attempt to persuade Bush to relax his opposition to the Kyoto treaty, which sets mandatory targets in cutting greenhouse gas emissions, when they gather today at the Group of Eight summit of leading industrial countries in Genoa, Italy. At the same time, delegates from 180 countries are meeting in Bonn in a bid to salvage the Kyoto protocol, which Bush renounced in March as "fatally flawed."
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