BEIJING, Aug. 21 (Xinhuanet) -- Global warming skeptics were provided ammunition recently when a former mining executive who manages a website dedicated to global warming noticed temperatures in NASA data made an odd jump between 1999 and 2000.

The blogger, Stephen McIntyre, reported the discrepancy to NASA scientists on Aug. 4, and they had corrected the data discovered in Goddard Institute for Space Studies data by the following Tuesday, thanking McIntyre via email for pointing out the error.

The discrepancy occurred because the source of U.S. temperature data was changed between 1999 and 2000. It was thought that the data were matched across the two sources, but there turned out to be a very subtle mismatch between the temperature records.

The adjustments that were made to the data were fairly small — the net effect was to reduce the U.S. temperature anomalies for the period between 2000 and 2006 by 0.15 degrees Celsius, on average, noted climatologist Gavin Schmidt of NASA Goddard (who is not directly involved with the temperature analyses) in the climate science blog he co-runs, RealClimate.org.

However, some blogging skeptics now assert these adjustments cast doubt on the conclusions of warming temperatures, because some of the anomalies were reduced such that certain years might not have been as warm as was originally thought. Numerous comments have been posted on RealClimate and global warming skeptic sites debating the import of the adjustments.

"Do you think we can now be "99 percent certain" that 1934 was the warmest year in the last 1,000 years, or are we still 99 percent certain that it was 1998. How certain are we of ANYTHING that [climate scientists] say, now?" wrote one poster on RealClimate.

"This particular issue didn't change the global mean except to the third decimal place," Schmidt said, as compared to the 0.1 to 0.2 degrees Celsius of warming observed per decade over the globe.

Schmidt also noted that with the numerous other lines of evidence that show that global warming is taking place, including melting sea ice, changing migratory patterns among animals and rising sea levels, small adjustments like that made to the GISS U.S. temperature series are insignificant.

"There's not going to be any statistical problem that's going make [global warming] go away," he said.

(Agencies)