2010 ties record for warmest year yet

El Ni±o heated things up even as global temperatures continue to rise

2010 has tied with 2005 as the hottest year on record, according to two new studies.

HOT TIMES Between 2000 and 2009, more of the globe warmed (red) than cooled (blue) compared with average temperatures from the baseline period 1951–1980. Robert Simmon; NASA GISS http://earthobservatory.nasa.gov/IOTD/view.php?id=47628

On January 12 NASA and the National Oceanic and Atmospheric Administration released their independent analyses of global surface temperature data for last year. Both found that 2010 was ever-so-slightly warmer than 2005. But the difference was not statistically large enough to declare 2010 the winner.

The warmth of 2010 is “not surprising, considering that global surface temperatures have been climbing,” says Deke Arndt, chief of the climate monitoring branch of NOAA’s National Climatic Data Center in Asheville, N.C. The last decade has been the warmest since record-keeping began in 1880.

Combined land and ocean surface temperatures across the globe in 2010 were 0.62 degrees Celsius higher than the 20th century average, the NOAA analysis reports. In the continuous United States, temperatures were 0.6 degrees above normal,making it the 23rd warmest year on record for the country. The Northern Hemisphere experienced its warmest year on record, while the Southern Hemisphere saw its sixth warmest.

The NASA analysis, produced by its Goddard Institute for Space Studies in New York City, uses the period from 1951 to 1980 as its baseline and found that, on a global scale, 2010 was about 0.74 degrees Celsius warmer than that average.

Last year saw plenty of meteorological oddities. Early in 2010, North America, Europe and other parts of the Northern Hemisphere experienced bitter cold and severe snowstorms — thanks mainly to a phenomenon known as the Arctic Oscillation, a pattern that lets cold air travel south from the pole. Summer heat waves then baked India, China and especially Russia, where at least 15,000 people died from the heat and related wildfires. Rainfall records show that it was globally the wettest year since 1900.

Hot on the heels of 2010 and 2005 is 1998, ranked by both NOAA and NASA as the third-hottest year on record. “They all kind of looked like each other,” says Arndt. All three years began with a medium-to-strong El Ni±o, a climate pattern characterized by warmer-than-average sea surface temperatures in the eastern tropical Pacific Ocean. And during each of those years, the El Ni±o tapered off, to be replaced by the cooling influence of its counterpart La Ni±a.

In fact, the third main group that analyzes surface temperature trends earlier ranked 1998 as edging out 2005 for the top spot. That group, based at the Met Office Hadley Centre in Exeter, England, has not yet released its final ranking for 2010.

All three groups use slightly different techniques to analyze a host of observations from ground stations, ships, buoys and satellites. For instance, if there is a gap in measurements at a particular station — say, in the Arctic, where monitoring stations are few and far between — the Hadley researchers leave that station blank when doing their analyses. But NASA and NOAA, in slightly different ways from each other, use data from the closest stations to take an informed guess as to what the missing station data might be.

All the bean counting about which particular year is the hottest obscures a more profound point, says Gavin Schmidt, a climatologist at the NASA Goddard center who was not involved in the recent temperature analysis. “The baseline is getting warmer and warmer every year,” he says. Indeed, 2010 was the 34th year in a row in which global temperatures were higher than the 20th century average.

Schmidt predicts that 2011 will not be as toasty as 2010 was, in part because of the La Ni±a that is currently cooling things down. But because levels of heat-trapping greenhouse gases continue to rise in the atmosphere, “it’s almost certain to still be a top-10 year,” he says. “Maybe even a top-five year.”

Alexandra Witze is a contributing correspondent for Science News. Based in Boulder, Colo., Witze specializes in earth, planetary and astronomical sciences.

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