In fact, on average it was the fourth-hottest year around the planet since modern record-keeping began in 1880.
According to Schmidt, the warming has been driven in large part by increased emissions into the atmosphere of carbon dioxide and other greenhouse gases caused by human activities.
In 2015, nearly 200 governments adopted the Paris climate agreement to phase out the use of fossil fuels and limit the rise in temperatures between 1.5C to 2C, to avert "dangerous" man-made climate change. "We are seeing more and more warming that is happening at a faster and faster rate".
Weather dynamics mean warming affects regions in different ways. The long-term trends are extremely robust. 2016, boosted by a strong El Nino that normally tips the mercury northwards, remains the hottest year on record.
A total of 6,300 weather stations, ship and buoy observations of sea surface temperatures, and Antarctic research stations were used in NASA's analyses.
The two agencies use much of the same data but perform independent analyses with minor differences in methods that yield slightly different rankings.More news: Sen. Warren's expected 2020 bid banking on populist appeal
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The U.S. temperature in 2018 was the 14th warmest on average, said NOAA climate monitoring chief Deke Arndt.
Below is a statement by Brenda Ekwurzel, director of climate science and senior climate scientist at the Union of Concerned Scientists (UCS).
It was also an expensive year for natural disasters. "That's a clear upward signal".
NASA and NOAA climate scientists said even though 2018 was a tad cooler than the three previous years that was mostly due to random weather variations.
"If there was no warming of average temperatures, there would be about an even chance of a daily record high maximum or daily record low minimum occurring", said Meehl, who was not involved in the report.
Last year was also the third wettest on record in the U.S. Nine eastern states had their wettest years on record, "an exclamation point on a trend of big rain" in the age of climate change, Arndt said. The World Meteorological Organization? and the United Kingdom's Met Office? also found that 2018 was among the top four warmest years.