Statisticians reject global cooling with analysis showing a warming Earth

That led to a sharp rebuke from the Union of Concerned Scientists, which said the book mischaracterizes climate science with “distorted statistics.”

Levitt, a University of Chicago economist, said he does not believe there is a cooling trend. He said the line was just an attempt to note the irony of a cool couple of years at a time of intense discussion of global warming. Levitt said he did not do any statistical analysis of temperatures but “eyeballed” the numbers and noticed 2005 was hotter than the last couple of years. Levitt said the “cooling” reference in the book title refers more to ideas about trying to cool the Earth artificially.

Statisticians say that in sizing up climate change, it's important to look at moving averages of about 10 years. They compare the average of 1999-2008 to the average of 2000-2009. In all data sets, 10-year moving averages have been higher in the last five years than in any previous years.

“To talk about global cooling at the end of the hottest decade the planet has experienced in many thousands of years is ridiculous,” said Ken Caldeira, a climate scientist at the Carnegie Institution at Stanford University.

Ben Santer, a climate scientist at the Department of Energy's Lawrence Livermore National Lab, called it “a concerted strategy to obfuscate and generate confusion in the minds of the public and policy-makers” ahead of international climate talks in December in Copenhagen.

President Barack Obama weighed in on the topic Friday at the Massachusetts Institute of Technology. He said some opponents “make cynical claims that contradict the overwhelming scientific evidence when it comes to climate change, claims whose only purpose is to defeat or delay the change that we know is necessary.”

Early this year, climate scientists in two peer-reviewed publications statistically analyzed recent years' temperatures against claims of cooling and found them invalid.

Not all skeptical scientists make the flat-out cooling argument.

“It pretty much depends on when you start,” wrote John Christy, the Alabama atmospheric scientist who collects the satellite data that skeptics use. He said in an e-mail that looking back 31 years, temperatures have gone up nearly three-quarters of a degree Fahrenheit (four-tenths of a degree Celsius). The last dozen years have been flat, and temperatures over the last eight years have declined a bit, he wrote.

Oceans, which take longer to heat up and longer to cool, greatly influence short-term weather, causing temperatures to rise and fall temporarily on top of the overall steady warming trend, scientists say. The biggest example of that is El Nino.

El Nino, a temporary warming of part of the Pacific Ocean, usually spikes global temperatures, scientists say. The two recent warm years, both 1998 and 2005, were El Nino years. The flip side of El Nino is La Nina, which lowers temperatures. A La Nina bloomed last year and temperatures slipped a bit, but 2008 was still the ninth hottest in 130 years of NOAA records.

Of the 10 hottest years recorded by NOAA, eight have occurred since 2000, and after this year it will be nine because this year is on track to be the sixth-warmest on record.

The current El Nino is forecast to get stronger, which probably will push global temperatures even higher next year, scientists say. NASA climate scientist Gavin Schmidt predicts 2010 may break a record, so a cooling trend “will be never talked about again.”

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