2015 was hottest year in recorded history: Scientists
WASHINGTON — Scientists reported yesterday that 2015 was the hottest year in recorded history by far, breaking a record set only the year before — a burst of heat that has continued into the new year and is roiling weather patterns all over the world.
In the continental United States, the year was the second-warmest on record, punctuated by a December that was both the hottest and the wettest since record-keeping began. One result has been a wave of unusual winter floods coursing down the Mississippi River watershed.
Scientists started predicting a global temperature record months ago, in part because an El Nino weather pattern, one of the largest in a century, is dumping an immense amount of heat from the Pacific Ocean into the atmosphere. But the bulk of the record-setting heat, they say, is a consequence of the long-term planetary warming caused by human emissions of greenhouse gases.
“The whole system is warming up, relentlessly,” said Dr Gerald A Meehl, a scientist at the National Center for Atmospheric Research in Boulder, Colorado. It will take a few more years to know for certain, but the back-to-back records of 2014 and 2015 may have put the world back onto a trajectory of rapid global warming, after period of relatively slow warming dating to the last powerful El Nino, in 1998.
Politicians attempting to claim that greenhouse gases are not a problem seized on that slow period to argue that “global warming stopped in 1998” and similar statements, with these claims reappearing recently on the Republican presidential campaign trail.
Statistical analysis suggested all along that the claims were false, and the slowdown was, at most, a minor blip in an inexorable trend, perhaps caused by a temporary increase in the absorption of heat by the Pacific Ocean.
“Is there any evidence for a pause in the long-term global warming rate?” said Dr Gavin A Schmidt, head of the National Aeronautics and Space Administration’s (NASA) climate-science unit, the Goddard Institute for Space Studies, in Manhattan. “The answer is no. That was true before last year, but it’s much more obvious now.”
Dr Michael E Mann, a climate scientist at Pennsylvania State University, calculated that if the global climate were not warming, the odds of setting two back-to-back record years would be remote, about one chance in every 1,500 pairs of years. Given the reality that the planet is warming, the odds become far higher, about one chance in 10, by Dr Mann’s calculations.
Two American government agencies, NASA and NOAA, the National Oceanic and Atmospheric Administration, compile separate analyses of the global temperature, based upon thousands of weather stations and ocean buoys scattered around the world. They released their results yesterday, showing 2015 as the warmest year in a global record that began in 1880. Preliminary data from the Japan Meteorological Agency also show record warmth for 2015, and a British monitoring program is expected to report a similar result in coming weeks.
NOAA previously reported that 2015 was the second-warmest year for the continental US, after 2012.
The intense warmth of 2015 contributed to a heat wave in India last spring that turns out to have been the second-worst in that country’s history, killing an estimated 2,500 people.
The strong El Nino has continued into 2016, raising the possibility that this year, too, will set a global temperature record. The El Nino pattern is also disturbing the circulation of the atmosphere, contributing to worldwide weather extremes that include a drought in southern Africa, threatening the food supply of millions.