2015 was Earth's hottest year on record, and it appears the planet is still getting hotter.
Barely three weeks into the new year, climate researchers from NASA and the National Oceanic and Atmospheric Administration are already predicting that the average surface temperature around the planet is likely to be higher in 2016 than it was in 2015. That would mark the first time the average global temperature reached record-breaking heights for three consecutive years.
"It's not unprecedented to have two years in a row of record-breaking temperatures, but in our records, we've never had three years in a row," climatologist Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in New York, said Wednesday. "If 2016 turns out to be as warm as we anticipate, that would be unprecedented in our record book."
One reason scientists expect 2016 to be even warmer than 2015 is that the lingering effects of the El Niño weather pattern should push temperatures skyward through the first half of the year.
"El Niño takes heat out of the oceans and puts it in our atmosphere, and we've just had the biggest El Niño in a generation," said Katharine Hayhoe, an atmospheric scientist at Texas Tech University.
El Niño is partially responsible for the extremely high temperatures recorded around the globe in October, November and December, the NASA and NOAA researchers said. Still, even before the effects of El Niño were felt, the planet was experiencing considerable temperature anomalies.
Data show that 10 out of 12 months in 2015 broke previous temperature records. The only two that didn't were January and April.
"Even without El Niño this would have been the warmest year on record," Schmidt said. "We are looking at a long-term trend, and the factors that cause this long-term trend are continuing to accelerate, namely the increased burning of carbon dioxide fuels and other emissions."
Unusually warm temperatures were seen almost uniformly around the planet in 2015. Temperatures were well above the 20th century average on all six populated continents and in most of the oceans, the government scientists said.
The one exception was a curious region of unusually cool water in the Northern Atlantic, off the western coast of Greenland. Researchers are still trying to understand what's responsible for this cold spot, although the melting of the Greenland ice sheet might have something to do with it.
"It's something to look at going forward," Schmidt said.
On land, Asia and South America both saw their warmest years since official record keeping began there in 1910, while Africa and Europe reported their second-warmest years on record. North America had its fifth-warmest year, and Australia and the rest of Oceania reported its sixth-warmest year.
Two weeks ago, NOAA announced that the average temperature for the contiguous United States last year was 54.4 degrees Fahrenheit, 2.4 degrees above the 20th century average. That made 2015 the second-warmest year in 121 years of record keeping.
The global temperature data are collected by 6,300 land-based weather stations, as well as research stations in Antarctica and a network of ships and satellite-communicating buoys in oceans around the world.
NASA and NOAA have slightly different ways of interpreting surface temperature data, but they found comparable increases in average global temperature between 2014 and 2015. Specifically, NASA recorded an increase of 0.23 of a degree Fahrenheit, while NOAA measured a rise of 0.29 of a degree.
Although these changes may seem small, experts said they are both significant and unprecedented.
"For every 1-degree Fahrenheit increase in temperature, the atmosphere can hold about 4% more moisture," said Kevin Trenberth, a climate researcher at the National Center for Atmospheric Research in Boulder, Colo. "With a quarter-degree increase, that means the atmosphere can hold 1% more moisture in 2015 than in 2014."
One of the consequences of that is increased flooding. Devastating floods in Missouri, central South America and Chennai in southeast India in 2015 could have been the result of the higher global temperatures, Trenberth said.
"A quarter of a degree increase is actually huge," he said. "It's bigger than we've ever seen before."
The first detailed global temperature measurements were recorded in 1880. Since then, nine of the 10 warmest years on record have occurred since 2002, according to NOAA. The one exception is 1998, which ranks as the fifth-warmest year in part because of a particularly strong El Niño phase.
The British national weather service, the Met Office, released similar findings about global temperatures on Wednesday, saying 2015 broke records going back to 1850. The Japan Meteorological Agency has also published preliminary findings that show 2015 was on track to be the warmest year since 1891.
Tom Karl, director of NOAA's National Centers for Environmental Information in Asheville, N.C., said the streak was likely to continue this year.
"The odds favor 2016 being warmer than 2015," he said.
Schmidt said he wouldn't bet against that prediction.
"I'd give you better than even that will be the case," he said.
While most climatologists agree that more record-breaking years are sure to come, not all of them expect 2016 to be warmer than 2015.
Tim Barnett, a marine physicist with the Scripps Institution of Oceanography at UC San Diego, said his models predicted "a whopping cold event in the second half of 2016 that would temper or cancel out some of the effects of the El Niño in the first months of the year."
Regardless of what happens in 2016, scientists who follow the global climate said the announcement that 2015 was the warmest on record did not come as a surprise to them.
"We have this monster El Niño superimposed on a long-term warming trend due to human emissions of carbon dioxide," Texas Tech's Hayhoe said. "We saw this coming months ago.
"What did surprise people was how it surpassed the record — it didn't just break it, it smashed it," she added. "That's what we're going to see going forward. Global warming doesn't mean every year will be successively warmer than the previous one, but we will be breaking the record more and more frequently."
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