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With Climate Change, Long-Term Trends Are Key

(Originally published on Washington Post's Capital Weather Gang blog)

As the start of the New Year rapidly approaches, you're going to hear conflicting news about whether 2010 was the warmest year in the instrumental record. The first salvo has already been fired.

On Friday, NASA reported that the "meteorological year" spanning from December 2009 to November 2010 was the warmest in that agency's 131 years of record keeping. Never mind that the meteorological year is relevant only to meteorologists - the news still made headlines.

December 2009 to November 2010 surface temperature anomalies (or departures relative to a 1951-80 average) in the preliminary Goddard Institute for Space Studies analysis from NASA. Yellow, orange, and red regions all recorded warmer than average temperatures.

The two other groups that maintain official global surface temperature data - the U.S. National Oceanic and Atmospheric Administration (NOAA) and the UK Met Office Hadley Centre, which works in conjunction with the University of East Anglia Climatic Research Unit - will soon release data that may conflict with NASA somewhat, by ranking 2010 differently. NOAA, for example, currently ranks 1998 as the warmest year on record, rather than 2005, which is in NASA's top spot.

So, what should you, dear readers, make of the varying rankings? And does it really matter if 2010, compared to 2005 or 1998, was officially number one?

The bottom line is that all of the data as measured by land, sea, air, and even from space, shows 2010 has been an unusually warm year globally. This can be partially linked to El Nino conditions that were present up until last spring, but also to increasing concentrations of greenhouse gases in the atmosphere, which scientists say are very likely responsible for a large portion of the long-term warming trend.

This year's warmth is especially noteworthy because 2010 fell in a period of lower solar irradiance, which can help cool the climate. "The new record temperature in 2010 is particularly meaningful because it occurs when the recent minimum of solar irradiance is having its maximum cooling effect," wrote James Hansen, longtime director of NASA's Goddard Institute for Space Studies, along with three colleagues.

Read the full post at Washington Post's Capital Weather Gang blog.

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