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NASA said records show 2009 was tied for the second warmest since 1880 and in the Southern Hemisphere, 2009 was the warmest year on record.
Although 2008 was the coolest year of the decade because of a strong La Nina that cooled the tropical Pacific Ocean, 2009 saw a return to a near-record global temperatures as the La Nina diminished, according to analysis by NASA's Goddard Institute for Space Studies (GISS) in New York. The past year was a small fraction of a degree cooler than 2005, the warmest on record, putting 2009 in a virtual tie with a cluster of other years --1998, 2002, 2003, 2006, and 2007 -- for the second warmest on record.
NASA’s GISS said it uses publicly available data from three sources to conduct its temperature analysis. The sources include weather data from more than a thousand meteorological stations around the world, satellite observations of sea surface temperatures, and Antarctic research station measurements, GISS stated.
NASA also points out that other research groups also track global temperature trends but use different analysis techniques. The Met Office Hadley Centre in the United Kingdom uses similar input measurements as GISS, for example, but it omits large areas of the Arctic and Antarctic where monitoring stations are sparse, NASA stated.
Although the two methods produce slightly differing results in the annual rankings, the decadal trends in the two records are essentially identical, GISS stated.
"There's a contradiction between the results shown here and popular perceptions about climate trends," said James Hansen, GISS director in a statement. "In the last decade, global warming has not stopped."
According to a New York Times story, Hansen has often been attacked by skeptics of global warming for what they charge is selective use of temperature data. The question of whether the planet is heating and how quickly was at the heart of the so-called “climategate” controversy that arose last fall when hundreds of e-mail messages from the climate study unit at the University of East Anglia in England were released without authorization.