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Temperatures during the past decade have been the highest recorded

Last year was tied for the second warmest year since modern temperature record keeping began, and was the hottest in the southern hemisphere, according to a new analysis for the National Aeronautics and Space Administration.

Reaffirming the warming trend, NASA confirmed that globally, temperatures during the past decade have been the highest recorded, although the agency noted that accurate instrumentation to chart weather and climate patterns only became widely available in 1880.

In that time, average global temperatures have risen about 1.4 degrees F. (0.8 C), according to the agency. Almost half that increase has occurred in the past 30 years, after a lull in the middle of the 20th Century.

"In the last decade, global warming has not stopped," he said.

Global temperatures during 2009 were fractionally lower than 2005, the hottest overall year on record, according to the report. Last year's heat tied several other years from 1998 to 2007 in the rankings.

In the NASA statement, Hansen said it is more important to look at the trend that at any given year, when variable climate cycles can skew the data.

"There's substantial year-to-year variability of global temperature caused by the tropical El Niño-La Niña cycle," Hansen said. "But when we average temperature over five to 10 years, we find that global warming is continuing unabated."

Another Goddard climatologist, Gavin Schmidt, called the focus on annual numbers a distraction. Such short-term measurements amount to "noise," while the crucial information is the longer trend, he said.

That argument serves a political purpose as well as a scientific one. During the past year, American commentators who question global warming have pointed out that 1998 average temperatures were higher than those in 2008.

But those opinions omit a key fact, since 2008 was a time of strong cooling in the Pacific Ocean, which is susceptible to the surface water current cycles known as El Nino and La Niña. La Niña occurs when upwelling cold water spreads west in the Pacific from the coast of Peru. It tends to depress temperatures.

A La Niña phase ended early in 2009, replaced in the fall by an El Niño effect, which is caused when warm water spreads from the same area off Peru. Scientists predict it will continue this year. If that holds true, NASA said the Goddard group expects 2010 to be the hottest year on record.

Another reason for that projection is that last year's hot weather came in the face of a slight drop in energy output from the sun. Periods when there are few sunspots normally produce a fractional cooling in earthly temperatures.

"In 2009, it was clear that even the deepest solar minimum in the period of satellite data hasn't stopped global warming from continuing," Hansen said.

— JOE TYRRELL, NEWJERSEYNEWSROOM.COM