Last decade was the warmest ever, says NASA

From an Agence France-Presse article posted on Grist:

WASHINGTON—The past decade was the warmest ever, according to a new analysis of global surface temperatures released by NASA.

The U.S. space agency also found that 2009 was the second-warmest year on record since modern temperature measurements began in 1880. Last year was only a small fraction of a degree cooler than 2005, the warmest yet, putting 2009 in a virtual tie with the other hottest years, which have all occurred since 1998.

According to James Hansen, who heads NASA’s Goddard Institute for Space Studies, global temperatures change due to variations in ocean heating and cooling. “When we average temperature over five or 10 years to minimize that variability, we find global warming is continuing unabated,” Hansen said in a statement.

A strong La Niña effect that cooled the tropical Pacific Ocean made 2008 the coolest year of the decade, according to the New York-based institute.

In analyzing the data, NASA scientists found a clear warming trend, although a leveling off took place in the 1940s and 1970s. The records showed that temperatures trended upward by about 0.36 degrees F per decade over the past 30 years. Average global temperatures have increased a total of about 1.5 degrees F since 1880.

“That’s the important number to keep in mind,” said Gavin Schmidt, a climatologist with the institute. “The difference between the second and sixth warmest years is trivial because the known uncertainty in the temperature measurement is larger than some of the differences between the warmest years.”

Last year’s near-record temperatures took place despite an unseasonably cool December in much of North America and a warmer-than-normal Arctic, with frigid air from the Arctic rushing into the region while warmer mid-latitude air shifted northward, the institute said.