Jeff Tollefson in Nature:
It’s official: 2015 was the hottest year on record. Global data show that a powerful El Niño, marked by warmer waters in the tropical Pacific Ocean, helped to drive atmospheric temperatures well past 2014's record highs. Some researchers suggest that broader Pacific trends could spell even more dramatic temperature increases in years to come. Released on 20 January, the global temperature data come from three independent records maintained by NASA, the US National Oceanic and Atmospheric Administration (NOAA) and the UK Met Office. All three data sets document unprecedented high temperatures in 2015, pushing the global average to more than 1 ºC above pre-industrial levels. Although El Niño boosted temperatures late in the year, US government scientists say that the steady increase in atmospheric greenhouse gases continues to drive the longer-term trend. “The reason why this is such a warm record year is because of the long-term trend,” says Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies in New York. “And there is no evidence that this long-term trend has slowed.”
Average global surface temperatures in 2015 were 0.16 °C warmer than in 2014, which was previously the warmest year on record, according to NOAA. Virtually all areas of the globe, including land and oceans, experienced above-normal temperatures. Satellite and balloon records of temperatures in the upper atmosphere showed less warming due to a delayed response to El Niño, but are expected to rise faster in 2016. Overall, global temperatures have increased by 0.1 to 0.2 ºC per decade since the 1970s, says Thomas Karl, director of NOAA’s National Centers for Environmental Information in Ashville, North Carolina. “Clearly the 2015 data continues the pattern,” Karl said. “This trend will continue.”
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