Earth's surface temperatures in 2015 were the warmest since modern-day record keeping began in 1880, two U.S. government agencies reported Wednesday.
Even without naturally occurring warming trends, such as El Nino, 2015 would have been hotter than 2014, also a record-setter, NASA and the National Oceanic and Atmospheric Administration told reporters during a conference call.
Most of the heating is due to the combined effects of deforestation with the burning of fossil fuels, leaving more heat-trapping carbon dioxide and other greenhouse gases in the atmosphere, said Gavin Schmidt, head of NASA's Goddard Institute for Space Studies in New York.
"Even without El Nino, this would have been the warmest year on record," Schmidt said.
El Nino, a tropical Pacific Ocean warming system that kicked in during the last three months of 2015 and remains strong, portends an even warmer 2016.
"If you're going to be betting, you'd bet that it's going to be warmer than 2015," said Thomas Karl, director of NOAA's National Centers for Environmental Information in Asheville, North Carolina.