The year 2023 was the warmest on record, according to analyses of global temperatures from NASA and NOAA. Scientists aren’t sure why temperatures were so anomalous.
“We’re frankly astonished.”
“We’re frankly astonished,” said Gavin Schmidt, an author on NASA’s temperature analysis and a climate scientist at NASA’s Goddard Institute for Space Studies, at a press conference.
NASA’s and NOAA’s analyses, as well as a report from climate research nonprofit Berkeley Earth, all released Friday, concur that 2023 was a scorcher. NASA and NOAA scientists found that average temperatures were 0.15°C–0.16°C (0.27°F–0.29°F) warmer than temperatures in 2016, the previous hottest year ever recorded.
That’s a huge jump, because most records are set on the order of hundredths of degrees Celsius, said Russell Vose, a climate scientist at NOAA and an author on the agency’s analysis, at a press conference.
Berkeley Earth’s report concluded that 2023 was the first year to breach the 1.5°C (2.7°F) warming limit set by the Paris Agreement, a legally binding international treaty on climate change. NOAA’s and NASA’s analyses did not find that 2023 breached the 1.5°C limit, but “things are starting to approach that threshold,” Vose said at a press conference.
The European Union’s Copernicus Climate Change Service reported similar results Tuesday. Analyses from Berkeley Earth, NOAA, NASA, and the Copernicus Climate Change Service generally agreed, Vose said at a press conference.
“We’re still continuing to put greenhouse gases into the atmosphere,” Schmidt said. “As long as we continue to do that, temperatures will rise.”
The Berkeley Earth report suggested that the record-breaking temperatures in 2023 were driven by an El Niño event, in which the Pacific Ocean warmed and trade winds weakened.
The state of the La Niña–El Niño cycle, also called the El Niño–Southern Oscillation, or ENSO, in the spring is usually the best predictor of the year’s temperatures, Schmidt said at a press conference. In February and March of 2023, the world was still in the La Niña phase, leading scientists to think the rest of the year would be relatively cool.
“We’ve had bigger El Niños before. And they’ve never had that kind of impact on the global mean temperature.”
“The expectation we had about how ENSO affects the global temperature…was totally reversed [last] year,” Schmidt said at a press conference.
El Niño alone is also not enough to explain last year’s high temperatures, Schmidt said, and scientists don’t have a clear explanation. “We’ve had bigger El Niños before. And they’ve never had that kind of impact on the global mean temperature,” he said at a press conference.
Water vapor released into the atmosphere from the Hunga Tonga–Hunga Ha‘apai eruption in January 2022 could have contributed, Vose said at a press conference, adding that a slight decrease in aerosols may have also played a role.
The 2023 anomaly should be a “wake-up call” for climate scientists that there’s still much to learn about how the global climate functions, Schmidt said.
“It remains to be seen if 2023 is merely an unusual outlier or if it is an indication of unexpected changes ahead,” said Robert Rohde, a climate scientist at Berkeley Earth and an author on the report, in a statement.
“Our normal explanation for what’s going on does not work this year, and I think that there is a lot more work that needs to be done to really understand what happened in 2023,” Schmidt said at a press conference.
—Grace van Deelen (@GVD__), Staff Writer