New York saw a heatwave in early September Gary Hershorn/Getty Images
September was the most abnormally warm month ever observed, smashing the previous high for this month and putting 2023 on track to be the hottest year on record.
The global average surface air temperature last month was 16.38°C (61.48°F), according to the European Union’s Copernicus Climate Change Service. That beat the previous September record by 0.5°C, the widest such margin for any month in records going back to 1940, and exceeded the pre-industrial average for the month by 1.8°C. Zeke Hausfather at the Berkeley Earth research organisation in California called the anomaly “absolutely gobsmackingly bananas”.
“It’s now hard to imagine that global temperatures won’t break the record this year, and probably not by a small amount,” says Jennifer Francis at Woodwell Climate Centre in Massachusetts.
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This year so far has been 1.4°C warmer than the pre-industrial average, well above the anomaly seen in the hottest year, 2016, and a step closer to the threshold of 1.5°C of long-term warming at which severe impacts are predicted.
High temperatures throughout September drove extreme weather worldwide. Record heatwaves struck the UK, the US and Europe. Wildfire season started early in Australia. Cyclone Daniel, fuelled by exceptionally warm Mediterranean waters, killed thousands of people in Libya, and two deadly typhoons hit China in one week.
“It’s all connected,” says Francis. “Warming increases the chances of broken temperature records, but it also means more evaporation of water vapour from land and oceans into the air.”
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This year also saw the hottest July and August on record. Unseasonable warmth is expected to continue with the onset of El Niño, the climate phase in which warm water pools in the eastern Pacific, boosting the global temperature. As October begins, unusual warmth is bringing a “second summer” to swathes of North America and Europe.
Ongoing marine heatwaves are adding even more energy to the mix, with sea surface temperatures across much of the world also setting a September record.
“The ocean is starting from a warmer place for this El Niño event, so 2024 is likely to be even warmer again than 2023,” says Samantha Burgess at Copernicus. “Every fraction of a degree matters, and every action that we take to get closer to net zero matters.”
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