According to independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA), Earth’s 2015 surface temperatures were the warmest since modern recordkeeping began in 1880.
Globally-averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.23°F. Only once before, in 1998 (another El Niño-influenced year), has the new record been greater than the old record by this much.
The 2015 temperatures continue a long-term warming trend, according to analyses by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York (GISTEMP).
NOAA scientists concur with the finding that 2015 was the warmest year on record based on separate, independent analyses of the data. Because weather station locations and measurements change over time, there is some uncertainty in the individual values in the GISTEMP index. Taking this into account, NASA analysis estimates 2015 was the warmest year with 94% certainty.
Phenomena such as El Niño or La Niña, which warm or cool the tropical Pacific Ocean, can contribute to short-term variations in global average temperature. A warming El Niño was in effect for most of 2015.
Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, NASA and NOAA found that the 2015 annual mean temperature for the contiguous 48 United States was the second warmest on record.