The global average temperature for September broke records by such an absurd margin that climate experts are struggling to describe the phenomenon.
“This month was — in my professional opinion as a climate scientist — absolutely gobsmackingly bananas,” Zeke Hausfather, a researcher with Berkeley Earth, said on the social media platforms Bluesky and X.
The numbers are stark. September 2023 beat the previous record for the month, set in 2020, by 0.5C (0.9F), according to data sets maintained by the Japan Meteorological Agency and the EU’s Copernicus Climate Change Service. The temperature anomaly for the month was roughly 1.7C above pre-industrial levels, which is above the symbolic 1.5C mark set as the stretch goal in the Paris Agreement.
“We’ve never really seen a jump anything quite of this magnitude,” Hausfather said. “Half a degree C is analogous to slightly less than half of all the warming we’ve seen from pre-industrial [temperatures].”
Carbon dioxide emissions from burning fossil fuels are the main driver of rising temperatures. The global average temperature this year has also seen a boost from El Niño, a natural climate shift in the Pacific. Other factors may also be pushing temperatures up incrementally, such as a decline in cooling aerosol pollution from ships.
Hausfather said next September may be unlikely to have all the same compounding factors, and consequently may be not as extreme. But either way, he described September 2023 as a “sneak peek” of what the back-to-school month may feel like in a decade as climate change pushes temperatures higher.
The sizzling September follows what was the hottest summer on record. The widespread and enduring heat means an estimated 1.5 billion people felt “a very strong influence of climate change” every day between June and August, according to an analysis by the nonprofit Climate Central. Relentless warmth continued last month with particularly intense weather in Europe.
Several entities around the world keep track of the world’s global average temperature. Agencies and universities have typically maintained datasets drawn from weather stations, airplanes, satellites, balloons, buoys and ships. These records are published monthly by the likes of NASA, the US National Oceanic and Atmospheric Administration, the University of East Anglia and Berkeley Earth. The differences among these independent analyses are slight — which is partially what gives scientists so much confidence in them. Those organizations’ global temperature analyses for September are expected to be released in the coming weeks.
The Japanese and EU data sets utilize a different process, called reanalysis, which employ powerful weather models to look backwards at what’s happened every hour globally, for decades, instead of forward, to produce forecasts for coming days.
By calling September “absolutely gobsmackingly bananas,” Hausfather, who is both a scientist and a frequent public communicator, has added a new entry into the eternal struggle to describe the scale of observable changes to the climate. It joins other efforts, such as Australia’s addition of a new color representing heat to its weather maps in 2013 and the Spanish city of Seville’s decision to name heat waves.
“Climate scientists are running out of superlatives to describe 2023,” Hausfather said.