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.
The independent studies by NASA and NOAA align with previously announced research by British and Japanese scientists, all showing Earth heating up to record levels in 2015.
"Clearly, the 2015 data continues the pattern we've seen over the last four to five decades," Karl said.
The warmer temperatures may impact the frequency, intensity and locations of extreme weather events, such as flooding and hurricanes. Global warming also is tied to Arctic ice melt and rising seas.
"This trend will continue ... because the factors that are causing this long-term trend are continuing to accelerate," Schmidt said.
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"We're mainly physical scientists, so we're just seeing what's going on and predicting what's ahead. It's really up to society and policy makers to decide what to do with that information," he added.
The new studies show that on average, Earth's surface temperature has risen by about 1.8 degrees Fahrenheit since the late-19th century.
Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. Last year was the first time the global average temperatures were 1 degree Celsius or more above the 1880-1899 average, NASA said.
The analysis is based on surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations.