2015 was the hottest year in the historical record, easily breaking the mark set only one year earlier. The unusually large El Niño weather pattern is releasing enormous amounts of heat from the Pacific Ocean into the atmosphere, but climate scientists say that the bulk of the record-setting heat is due to the long-term warming effects of greenhouse gas emissions. The global land surface temperature was 1.6°F above the 20th century historical average. That’s a huge jump from 2014, which was 1.3° above average. That may sound like very little, but for the planet as a whole, it is extremely large.