Aug. 14 (Bloomberg) -- NASA has revised climate data to show 1934 as the hottest year on record in the U.S., ousting 1998 and challenging the argument that national temperatures are reaching new highs amid global warming.

According to the figures released last week, four of America's 10 warmest years are now in the 1930s, during the Dust Bowl era. Just three years from the past decade remain among the top 10, with 2001 having fallen out entirely.

A flaw in the data, brought to light by a Canadian researcher, led the National Aeronautics and Space Administration to cut mean ``temperature anomalies,'' or deviations from the 30- year average, by 0.15 degree Celsius (0.27 degree Fahrenheit) from 2000 to 2006.

The researcher's Web site wasn't working today because of heavy traffic or an ``attack,'' according to a note on the home page. The site is run by Stephen McIntyre, a former president of Dumont Nickel Inc. and policy analyst with the Canadian government.

While the U.S. revision has only a small effect on worldwide mean temperature readings, skeptics of global warming have seized on it. Rush Limbaugh, the most listened-to radio host in the country, last week called global warming a ``hoax'' supported by shoddy science. The transcript is one the most popular stories on his show's Web site.

NASA climatologist James Hansen, director of the Goddard Institute for Space Studies in New York, dismissed his critics.

`Desperate Characters'

``These are some desperate characters trying to make a mountain out of a molehill,'' he said in an e-mail. ``If one instead looks at the temperature averaged over several years, it is apparent that the U.S. as well as the world has been quite warm in the past decade.''

NASA's Goddard Center lists 2005 as the world's warmest year, followed by 1998, 2002, 2003 and 2006.

Global-warming proponents have sought to link pollution from factories and cars with higher world temperatures, calling for government-imposed caps on so-called greenhouse gases.

The U.S produces about a quarter of the globe's carbon- dioxide emissions, though China will overtake the U.S. as the world's biggest emitter in two years, according to the International Energy Agency.

Two months ago, the U.S. blocked a Group of Eight attempt ago at creating a pledge to halve emissions by 2050, even as the European Union and Japan vowed to go ahead with their own cuts.

To contact the reporter on this story: Demian McLean in Washington at dmclean8@bloomberg.net.

Last Updated: August 14, 2007 17:19 EDT