The summary is a purely scientific document and does not offer any recommendations on ways to control the problem. Those are expected in a chapter to be released this year.
The obvious solution would be to cut emissions of carbon dioxide, the most important greenhouse gas, by reducing the use of fossil fuels in automobiles, factories and power plants.
The 1997 Kyoto Protocol was designed to reduce such emissions, but some major countries, including the United States, China and India, have no defined targets. President Bush withdrew the U.S. from the protocol in 2001, arguing that it was an "economic straitjacket" and that it failed to set standards for developing nations.
The earlier IPCC report was heavily criticized by conservative critics and a variety of online bloggers who said it exaggerated the effects of global warming. But a new study reported Thursday in the online version of the journal Science said that the IPCC report actually significantly underestimated both the extent of warming and the extent of the rise in sea levels.
An international team of climate experts said in the Science report that data showed global temperatures had increased by 0.6 degree, at the upper limit of the U.N.'s predictions, and that sea levels had risen 0.13 inch per year, compared with the U.N. report's estimate of less than 0.08 inch per year.
The data show that "IPCC is presenting a consensus view that has been OKd by a very large number of interests, so it tends to err on the side of making cautious statements and not exaggerating," said geochemist Ralph Keeling of the Scripps Institution of Oceanography in La Jolla, one of the authors of the Science study.
The Science study "looks quite solid to me, indicating ... that the climate is changing in a very significant way -- and model projections are not overestimates, as some charge," said atmospheric scientist Michael MacCracken of the Climate Institute, an independent think tank in Washington.
The unexpectedly large rise in sea levels may be at least partially due to the recently observed melting of the ice sheets, the authors of the Science study said.
The increase also may be due in part to a natural variability in sea levels superimposed onto rises produced by global warming, they said. It would be "premature," they concluded, to assume that sea levels will continue to increase at the current rate.
thomas.maugh@latimes.com
The Associated Press and Reuters were used in compiling this report.
