By Marc Kaufman
Washington Post Staff Writer
Wednesday, August 15, 2007
NASA has slightly revised its record of average annual temperatures in the United States since 2000 -- modifications that researchers say are insignificant but that some conservative commentators and bloggers have seized upon to assert that global warming has been hyped as a problem.
The revisions, which were first posted on the Web site of NASA's Goddard Institute for Space Studies, stemmed from an error noticed by Canadian blogger and global warming skeptic Stephen McIntyre. James Hansen, director of the institute, said McIntyre brought the error to the institute's attention, and the error was corrected.
Average annual temperatures are based on readings collected from many different sites. To compare these readings over time, scientists adjust them to take into account factors such as urbanization. Hansen said the mistake occurred because NASA scientists thought some readings they used in determining the average annual temperature after the year 2000 had been adjusted, when they had not been.
Hansen said that the corrected figures show that the past six years were 0.15 degrees centigrade cooler than reported. Hansen said that the change is insignificant in terms of global warming and altered the overall global mean temperatures by one-one-thousandth of a degree.
Conservative radio talk show host Rush Limbaugh used reports of the revisions to argue that climate change is a hoax perpetrated by scientists with liberal agendas.
"We have proof of man-made global warming," Limbaugh said on his show last Thursday. "The man-made global warming is inside NASA. The man-made global warming is in the scientific community with false data."
Hansen said that the critics were "making a mountain of a molehill."
"The change does nothing to our understanding of how the global climate is changing and is being used by critics to muddy the debate," he said.
Hansen said that NASA generally does not release or discuss national weather statistics because it is more concerned with global patterns. The agency that pays more attention to American temperature trends is the National Oceanic and Atmospheric Administration, which has said that most of the warmest years in the past century have been in the past 12 years.
Hansen said the revised data do nothing to change that overall trend.
Climate researchers have long known that the mid- and late 1930s were quite warm and that 1934 may have been the hottest year of the century -- although average temperatures in 1998 were statistically just as high. The revised data do not affect the debate over which of those years was warmer.
The Intergovernmental Panel on Climate Change reported earlier this year that global warming is definitely occurring and that greenhouse gases created by humans are the most likely cause.
Staff writer Christopher Lee contributed to this report.