Five-Year Average Global Temperature Anomalies from 1880 to 2010

NASA's announcement this year - that 2010 ties 2005 as the warmest year in the 131-year instrumental record - made headlines. But, how much does the ranking of a single year matter?

Not all that much, emphasizes James Hansen, the director of NASA's Goddard Institute for Space Studies (GISS) in New York City. In the GISS analysis, for example, 2010 differed from 2005 by less than 0.01°C (0.018°F), a difference so small that the temperatures of these two years are indistinguishable, given the uncertainty of the calculation.

Meanwhile, the third warmest year - 2009 - is so close to 1998, 2002, 2003, 2006, and 2007, with the maximum difference between the years being a mere 0.03°C, that all six years are virtually tied.

Even for a near record-breaking year like 2010 the broader context is more important than a single year. "Certainly, it is interesting that 2010 was so warm despite the presence of a La Niña and a remarkably inactive sun, two factors that have a cooling influence on the planet, but far more important than any particular year's ranking are the decadal trends," Hansen said.