The 2017 results make the past four years the hottest period in their 138-year archive.
2017 was among the hottest years ever recorded, government scientists reported Thursday.
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 have ever recorded.
“The planet is warming remarkably uniformly,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, on a call to share the results with reporters.
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.
The renewed evidence of climate change, driven by human emissions of greenhouse gases, comes as the Trump administration moves to open new areas for oil drilling and rolls back regulations that sought to reduce global warming. The administration said it would withdraw from the Paris climate agreement last year.
2017 was also a year of record breaking disasters affecting the United States, including devastating California wildfires and a trio of hurricanes that cost over $200 billion — events of the sort many experts fear may worsen as the planet warms.
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.
NASA found that 2017 was 1.6 degrees Fahrenheit (.9 degrees Celsius) above the average temperature from 1951 through 1980. 2016 was .99 degrees Celsius higher, and 2015 just .86 degrees Celsius higher, according to the agency.
“The annual change from year to year can bounce up and down. There is year to year variability, but the long term trends are very clear,” said Deke Arndt, who heads the global monitoring branch at NOAA’s National Centers for Environmental Information.
Before 2017, 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 had both agreed on their rankings as they occurred. 2017, in contrast, merely stayed within the elevated temperature range 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 substantially influenced by the periodic El Niño 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 Niño — but 2017’s temperature now comfortably surpasses it.
NASA and NOAA presented the following slide in a briefing Thursday to show the planet has continued to warm throughout fluctuations in this cycle in the Pacific Ocean:
NASA’s Schmidt noted El Nino probably boosted the temperatures of the warmest year on record, 2016, by .12 degrees, but did not affect 2017 at all — suggesting if not for natural variability, 2017 might have been the warmest year on record.
“This kind of analysis really brings it home that the warmth that we’re seeing are independent of this variation in the Pacific,” he said.
In another striking analysis of 2017’s heat, NOAA’s Arndt pointed out that according to his agency, the amount of heat being stored in the upper layer of the global ocean, between the surface and about 700 meters depth, was at its highest on record last year.
“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 NASA’s Schmidt. It is the third straight year in NASA’s records 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 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. 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.
Here, too, assessments of 2017 differ.
Remote Sensing Systems, which studies lower tropospheric temperatures using satellites, found 2017 was the second-hottest year in a record dating back to 1979, a pretty striking finding in that El Niño events tend to be amplified in the troposphere, and 2017 was not one.
“The near-record warmth of 2017 is notable because an El Niño event did not occur in 2017,” wrote RSS physicist Carl Mears. “The other 3 warmest years, 1998, 2010, and 2016, were El Niño years.”
A group of scientists at the University of Alabama-Huntsville who also track tropospheric temperatures by satellite instead put 2017 at 3rd place, rather than 2nd, behind 1998.