NASA: 2010 Warmest Year On Record

The two years differed by less than 0.018 degrees Fahrenheit. That difference is so small that it puts them in a statistical tie. In the new analysis, the next warmest years are 1998, 2002, 2003, 2006 and 2007, which are statistically tied for third warmest year. The GISS records begin in 1880.

To measure climate change, scientists look at long-term trends, and in this case used a 30-year period. Generally, to establish a change in climate, 30-year periods are used to check if one or more years is a fluke.

This analysis found 2010 approximately 1.34 degrees warmer than the average global surface temperature from 1951 to 1980. The temperature trend, including data from 2010, shows the climate has warmed by approximately 0.36 F per decade since the late 1970s.

If the warming trend continues, as is expected, if greenhouse gases continue to increase, the 2010 record will not stand for long, said James Hansen, the director of GISS in a statement.

The analysis produced at GISS is compiled from weather data from more than 1,000 meteorological stations around the world, satellite observations of sea surface temperature and Antarctic research station measurements. A computer program uses the data to calculate temperature anomalies -- the difference between surface temperature in a given month and the average temperature for the same period during 1951 to 1980. This three-decade period acts as a baseline for the analysis.

The resulting temperature record closely matches others independently produced by the Met Office Hadley Centre in the United Kingdom and the National Oceanic and Atmospheric Administration's National Climatic Data Center.

The record temperature in 2010 is also noteworthy because in the last half of the year there was a move to La Niña conditions, which bring cool sea surface temperatures to the eastern tropical Pacific Ocean.

Global temperature is rising as fast in the past decade as in the prior two decades, despite year-to-year fluctuations associated with the El Niño-La Niña cycle of tropical ocean temperature, Hansen and colleagues reported in the Dec. 14 issue of Reviews of Geophysics.

A chilly spell also struck this winter across northern Europe. That may have been linked to the decline of Arctic sea ice because of warming temperatures at higher latitudes. Arctic sea ice acts like a blanket, insulating the atmosphere from the ocean's heat. When it melts or never forms in the first place, the heat can escape into the atmosphere, increasing local surface temperatures. Regions in northeast Canada were more than 18 degrees warmer than normal in December.

The loss of sea ice may also be driving Arctic air into the middle latitudes. Winter weather patterns are notoriously chaotic, and the GISS analysis finds seven of the last 10 European winters warmer than the average from 1951 to 1980. The unusual cold in the past two winters has made scientists speculate about a potential connection to sea ice changes.

One possibility is that the heat source due to open water in Hudson Bay affected Arctic wind patterns, with a seesaw pattern that has Arctic air downstream pouring into Europe, Hansen said.