This visualization shows a long-term warming trend of the Earth, showing temperature changes from 1880 to 2015 as a five-year moving average. Orange colors represent temperatures that are warmer than the 1951-1980 baseline average, and blue represent temperatures cooler than the baseline.
Most of the warming has occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. Last year was the first time global mean temperatures were 1 degree Celsius or more above the middle 1880-1899. Phenomena such as El Niño or La Niña, which warm or cool the tropical Pacific Ocean, can contribute to short-term variations in global mean temperature. A warming El Niño was in effect for most of 2015. "2015 was remarkable even in the context of the current El Niño," said GISS Director Gavin Schmidt. "Last year's temperatures had an El Niño assist, but it is the cumulative effect of the long-term trend that has resulted in the warming record that we are seeing." Climate dynamics often affect regional temperatures, so not all regions of the Earth experienced record average temperatures last year. For example, NASA and NOAA found that the 2015 mean annual temperature for the 48 United States was the second warmest on record.