Confirming Long-Term Trend, 2018 Was Fourth Warmest Year on Record
Earth’s global surface temperatures in 2018 were the fourth warmest since modern record keeping began in the 1880s, according to independent analyses by NASA and the National Oceanic and Atmospheric Administration.
The 2018 temperatures rank just behind those of 2016, 2017 and 2015, and 2014 was the fifth warmest. Eighteen of the warmest 19 years have occurred since 2000; the other one was 1998.
Global temperatures in 2018 were 1.5 degrees Fahrenheit (0.83 degrees Celsius) warmer than the 1951 to 1980 mean, according to scientists at NASA’s Goddard Institute for Space Studies, an affiliate of Columbia University’s Earth Institute. “2018 is yet again an extremely warm year on top of a long-term global warming trend,” said Goddard Institute director Gavin Schmidt.
Since the 1880s, the average global surface temperature has risen about 2 degrees Fahrenheit (1 degree Celsius). According to scientific consensus, this warming has been driven in large part by increased emissions into the atmosphere of carbon dioxide and other greenhouse gases caused by human activities.
(Animation courtesy of NASA)
Weather dynamics often affect regional temperatures, so not every region experienced the same degree of warming. The NOAA analysis found the 2018 annual mean temperature for the contiguous 48 United States was only the 14th warmest on record; in other places, it was much hotter.
The analyses found that warming trends have been consistently strongest in the Arctic, where 2018 saw continuing loss of sea ice. In addition, mass loss from the Greenland and Antarctic ice sheets continued to contribute to sea level rise, and increased temperatures contributed to longer and more intense fire seasons, ranging from California to Australia.
“The impacts of long-term global warming are already being felt — in coastal flooding, heat waves, intense precipitation and ecosystem change,” said Schmidt.
NASA’s temperature analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations.
These raw measurements are analyzed using an algorithm that adjusts for the varied spacing of temperature stations around the globe and “heat island” effects produced by urban infrastructure that absorbs and then gives off large amount of solar energy.
Because weather station locations and measurement practices change over time, the interpretation of specific year-to-year global mean temperature differences has some uncertainties. Taking this into account, NASA estimates that 2018’s global mean change is accurate to within 0.1 degree Fahrenheit, with a 95 percent certainty level.
NOAA scientists used much of the same raw temperature data, but with a different baseline period and different interpolation into the earth’s polar regions and other data-poor areas. NOAA’s analysis found 2018 global temperatures were 1.42 degrees Fahrenheit (0.79 degrees Celsius) above the 20th century average.
Other major research institutions including the British and Japanese meteorological agencies came up with similar analyses late last month. Normally, the yearly NASA and NOAA announcements come out around the same time as the others’, but this year’s reports were delayed due to the partial U.S. government shutdown.