U.S. government scientists have declared 2015 to be the hottest year on record based on surface temperature readings, reaching 0.87 degrees Celsius above the 20th century average.
Last year’s record heat, however, was in part due to the strongest El Niño warming event in 18 years that lasted through most of 2015. Indeed, El Niño was to blame for the freakishly warm weather Americans experienced over the holidays.
Scientists with the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) found 2015 was about 0.13 degrees hotter than 2014 — that year was previously labeled as the warmest on record, but scientists were only 48 percent sure of it. Scientists say there’s only a 5 percent chance another year is warmer than 2015, thanks to a powerful El Niño.
“2015 was remarkable even in the context of the ongoing El Niño,” Gavin Schmidt, a NASA climate scientist, 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.”
El Niños are warming events that heat up the Pacific Ocean for months (sometimes longer) and raise the Earth’s average temperature. El Ninos come pretty regularly every few years, and there are even decades when El Niños are much more prevalent than their cooling counterparts — La Niñas.
There was an El Niño throughout most of 2015, according to NASA. The current El Niño was ranked the strongest such event in 18 years and isn’t expected to weaken until Spring 2016.
But while surface temperature readings showed 2015 to be the warmest on record, satellite temperature readings only found last year to be the third or fourth warmest on record.