The government agency made the announcement in a press release, noting that global temperatures 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 (GISS) in New York.
“2018 is yet again an extremely warm year on top of a long-term global warming trend,” said GISS Director Gavin Schmidt in the statement.
Collectively, the past five years are "the warmest years in the modern record," NASA added.
The government agency added that since the 1880s, the global temperature has risen approximately 2 degrees Fahrenheit. That's largely due to "increased emissions into the atmosphere of carbon dioxide and other greenhouse gases caused by human activities," Schmidt said.
NASA also said that since weather dynamics are often regional, not every region would experience a similar amount of warming. For the contiguous 48 states, 2018 was the 14th warmest on record.
Conversely, the Arctic region saw the strongest warming trends, with a loss in the Greenland and Antarctic ice sheets contributing to sea level rise. Higher temperatures can add to longer fire seasons and extreme weather events, Schmidt noted.
“The impacts of long-term global warming are already being felt — in coastal flooding, heat waves, intense precipitation and ecosystem change,” he said.
By the end of the century, ocean surface temperatures may rise as much as 4.8 degrees Fahrenheit, assuming a steady increase in carbon dioxide in the atmosphere, according to current climate models.
NASA's analysis came from 6,300 different inputs, including weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations.
Eighteen of the 19 warmest years on record have occurred since 2001, including 2016, which was the warmest year on record, due in part to the El Niño effect, a temporary change in the climate of the Pacific Ocean.
2018 was impacted by La Niña, which represents "periods of below-average sea surface temperatures across the east-central Equatorial Pacific," according to the National Oceanic and Atmospheric Administration.
NOAA also published data on 2018's temperatures, concurring with NASA that last year was the fourth-hottest year on record.