2017 Was the Second Hottest Year on Record
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Earth’s global surface temperatures in 2017 ranked as the second warmest since 1880, according to an analysis by scientists at NASA’s Goddard Institute for Space Studies (GISS). Continuing the planet’s long-term warming trend, globally averaged temperatures in 2017 were 0.90 degrees Celsius (1.62 degrees Fahrenheit) warmer than the 1951 to 1980 mean. That is second only to global temperatures in 2016.

In a separate, independent analysis, scientists at the National Oceanic and Atmospheric Administration (NOAA) concluded that 2017 was the third-warmest year in their record. The minor difference in rankings is due to slightly different methods used by the two agencies to analyze global temperatures. The long-term records of the two agencies remain in strong agreement, and both analyses show that the five warmest years on record have all taken place since 2010.

The map above depicts global temperature anomalies in 2017, according to the NASA GISS team. The map does not show absolute temperatures; instead, it shows how much warmer or cooler each region of Earth was compared to a baseline average from 1951 to 1980.

Because the locations and measurement practices of weather stations change over time, there are uncertainties in the interpretation of specific year-to-year global mean temperature differences. Taking this into account, NASA estimates that the 2017 global mean change is accurate to within 0.1 degree Fahrenheit, with a 95 percent certainty level.

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“Despite colder than average weather in any one part of the world,” said GISS Director Gavin Schmidt, “temperatures over the planet as a whole continue the rapid warming trend we have seen over the last 40 years.”

The animated figure above shows global temperature anomalies for every month since 1880, a result of the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) model run by NASA’s Global Modeling and Assimilation Office. Each line shows how much the global monthly temperature was above or below the annual global mean from 1980–2015. The column on the right lists each year when a new global record was set.

Earth’s average surface temperature has risen a little more than 1 degree Celsius (about 2 degrees Fahrenheit) during the past century or so, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. 2017 was the third consecutive year in which global temperatures were more than 1 degree Celsius (1.8 degrees Fahrenheit) above late 19th-century levels.

Phenomena such as El Niño and La Niña—which warm and cool the tropical Pacific Ocean and cause corresponding variations in global wind and weather patterns—contribute to short-term variations in global temperatures. Also, weather dynamics affect regional temperatures, so not every region on Earth experienced similar amounts of warming last year. Warming trends are strongest in the Arctic regions.

The NASA GISS team assembles its analysis from publicly available data acquired by roughly 6,300 meteorological stations around the world; from ship- and buoy-based instruments measuring sea surface temperature; and from Antarctic research stations. This raw data is analyzed using methods that account for the distribution of temperature stations around the globe and for urban heating effects that could skew the calculations. (For more explanation of how the analysis works, read World of Change: Global Temperatures.)

Analyses from the United Kingdom Met Office and the World Meteorological Organization also ranked 2017 among the top three warmest years on record. Scientists from NOAA, WHO, and the UK Met Office use much of the same raw temperature data, but with different baseline periods or slightly different methods to analyze Earth’s polar regions and global temperatures.

NASA Earth Observatory images by Joshua Stevens, based on data from the NASA Goddard Institute for Space Studies. Caption by Kate Ramsayer, NASA Goddard Space Flight Center, with Mike Carlowicz.

In situ Measurement

2017 Was the Second Hottest Year on Record

January 19, 2018
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