The National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration estimate with 94 percent certainty that 2015 was the warmest year on record, according to a statement released Wednesday.
The record for the hottest year on Earth was previously held in 2014. Last year's global average temperatures "shattered" that mark by 0.23 degrees Fahrenheit, or 0.13 Celsius. "Only once before, in 1998, has the new record been greater than the old record by this much," NASA's press release states.
According to NASA's analysis, El Niño, one of the strongest in history, likely contributed at least in part to last year's record-breaking temperatures. December 2015 was a particularly hot month in the United States; nearly 30 different states, mostly in the central and eastern parts of the country, experienced their warmest Decembers on record.
Scientists from NASA's Goddard Institute for Space Studies caution against placing the blame for 2015's unseasonable warmth solely on El Niño, however. Longer historic warming trends indicate that carbon dioxide emissions and other anthropogenic greenhouse gases are rapidly warming the planet—so it's not just complex weather systems like El Niño. According to NASA, 15 of the 16 warmest years on record have occurred since 2001.
"2015 was remarkable even in the context of the ongoing El Niño," GISS director Gavin Schmidt said in a statement. "Last year's temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing."
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