Government scientists reported Thursday that 2017 was among the hottest years ever recorded.
The year was the second-hottest in recorded history, NASA said, while scientists from the National Oceanic and Atmospheric Administration reported 2017 was the third-warmest they’ve ever recorded.
The two government agencies use different methodologies to calculate global temperatures, but by either standard, the 2017 results make the past four years the hottest period in their 138-year archive.
2017 achieved a temperature of 1.51 degrees Fahrenheit (0.84 degrees Celsius), above the average temperature seen in the 20th century, according to NOAA’s National Centers for Environmental Information.
The years 2014, 2015, and 2016 had set new all-time temperature records in stepwise fashion — culminating in a dramatic new high in 2016 — and NASA and NOAA agreed on their rankings as they occurred. 2017, in contrast, merely stayed within the elevated temperature range that these prior years had already established.
The difference between the two agencies in ranking 2017 is somewhat driven by the different methodology the two agencies use to measure temperatures in the Arctic, the fastest-warming part of the planet, said Zeke Hausfather, a climate scientist who also closely tracks annual temperatures with Berkeley Earth.
2017 was unequivocally the warmest year on record that was not influenced by the periodic El Nino phenomenon, which releases added warmth from the Pacific Ocean and was present in the record warm years of 2015 and 2016.
1998, for instance, was at the time a record year for global temperatures, as it coincided with a very strong El Nino — but 2017’s temperature now comfortably surpasses it.
“It’s unlikely we’ll ever see temperatures as cool as we had back before 2014 again,” said Hausfather, who commented on the NASA and NOAA numbers and also released his own group’s temperature record Thursday.
The result come in a big year for global climate diplomacy as countries seek to hew to the Paris climate goals of holding warming below 2 or perhaps 1.5 degrees Celsius above preindustrial levels.
2017 was 1.12 degrees Celsius above late 19th century temperatures, according to Gavin Schmidt, who directs NASA’s Goddard Institute for Space Studies. It’s the third straight year in NASA’s records that temperatures have eclipsed 1 degree Celsius above temperatures in the late 19th century.
“This year governments are due to start the process of assessing the size of the gap between their collective ambitions for reducing greenhouse gas emissions and the goals of the Paris Agreement,” said Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics and Political Science, in a statement.
“The record temperature should focus the minds of world leaders, including President Trump, on the scale and urgency of the risks that people, rich and poor, face around the world from climate change.”
NASA and NOAA, which both keep independent records of the Earth’s temperature, have adopted a practice in recent years of jointly announcing their numbers, even though they can differ.
In addition to the official U.S. agencies, a number of additional expert outlets have tracked temperatures and found results consistent with those of NOAA and NASA.
Hausfather’s group, Berkeley Earth, also found that 2017 was the second hottest year on record.
“The Arctic has warmed 2 and a half degrees C since the middle of the century,” he said. “It’s really warming faster than anywhere on earth. So much of the difference in 2017 between the groups that find it in second place and third place has to do with how the Arctic is handled.”
NOAA, NASA, and Berkeley Earth track temperatures at the surface of the Earth, over both land and oceans. But another way to track the planet’s warming is to analyze the temperature of the atmosphere at a significantly higher elevation, in the so-called “lower troposphere” extending from a little above the planet’s surface to several miles into the air.
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