The year 2017 was the second-warmest year on record, according to the scientists at NASA.

Since reliable record-keeping began in 1880, scientists have been keeping track of global temperatures. At the end of 2017, scientists at NASA calculated the global temperature and ranked it second on the warmest years list. The hottest year on record was the year prior; 2016.

The National Oceanic and Atmospheric Administration (NOAA), uses a different analytical method for calculating global temperatures, ranked 2017 as the third-warmest year on record.

Previously, the warmest years have occurred during the weather pattern known as El Niño. During El Niño years, the trade winds weaken or reverse causing cold parts of the ocean to warm up. Those warmer water temperatures lead to warmer atmospheric temperatures and a warmer year.

The year 2017 was an exception, because it was a La Niña year. In those years, the trade winds strengthen and the ocean waters are cooler than normal. Despite the extra cooling that should’ve occurred, 2017 still remained warm.

SEE ALSO: UK Watchdogs Call for 70 Percent of New Cars to be Zero Emission by 2030

To determine temperature, both NASA and NOAA use weather stations both on land and at sea. The difference in the final results comes from NASA giving the arctic regions more influence in the final calculation.

Despite differences in how they analyize the data, both NASA and NOAA have said that 17 of the 18 warmest years have occured since 2001. Global temperatures have increased by more than 1 degree Celsius since the beginning of record keeping.

Anthony Barnston, chief forecaster at the International Research Institute for Climate and Society at Columubia University doesn’t believe that 2018 will be a record breaking year. It’s another La Niña year.

“That will probably hold back the average mean temperatures from breaking records again,” Dr. Barnston said.

The New York Times