Both the U.S. space agency NASA and the National Oceanic And Atmospheric Administration (NOOAA) say that Earth's 2016 surface temperatures were the warmest since modern record-keeping began in 1880.

The globally averaged temperatures were 1.78˚F (0.99˚C) warmer than the mid-20th century mean.

Temperature hot spots in Africa.Temperature hot spots in Africa.Not only was 2016 the warmest year, but it was the third year in a row to set new records for global average surface temperatures.

According to scientists at NASA's Goddard Institute for Space Studies (GISS), the 2016 temperatures continue a long-term warming trend. Despite uncertainties in the interpretation of specific year-to-year global mean temperature differences, NASA estimates that their conclusions are valid with greater than 95% certainty.

"2016 is remarkably the third record year in a row in this series," says GISS Director Gavin Schmidt. "We don't expect record years every year, but the ongoing long term warming trend is clear."

Most of the warming has occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001.

Not every region on earth, however, experienced record average temperatures last year. For example both NASA and NOAA found the 2016 annual mean temperature for the contiguous 48 United States was the second warmest on record. In contrast the Arctic experienced its warmest year ever, consistent with a record for low sea ice found in that region for most of the year.

The raw temperature data used by NASA comes from 6300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Arctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions.