September 2024 was the planet’s second-hottest on record — and flooding risk is rising

The planet’s average temperature in September reached 16.17 °C, just shy of the record 16.38 °C set in September 2023. The European Union’s Climate Change Program reported the figure. Scientists say human-driven greenhouse gas emissions are behind the temperature anomalies. The Copernicus Climate Change Service (C3S) in Bonn reported that September 2024 was 1.54 °C warmer than the 1850–1900 average, the pre-industrial benchmark. “September 2024 became the second warmest month on record, both globally and in Europe,” said Samantha Burgess, deputy director of C3S.

Burgess said higher air temperatures made September exceptionally humid because warmer air holds more moisture, which leads to stronger rainfall and flooding. “The extreme downpours we are witnessing this month, which are becoming increasingly frequent, have intensified due to atmospheric warming; in just a few days, we received a month’s worth of rainfall,” she said. The risk of extreme precipitation will continue to climb as temperatures rise, but “the sooner we achieve net-zero emissions, the quicker we can reduce this risk,” she added.

Overall, the climate trend is worrying. Although this September wasn’t as hot as last year’s, C3S experts remain concerned about the warming trend pushing up the global average. The average global temperature over the past 12 months (October 2023–September 2024) is the second highest on record for any 12-month period. C3S climatologists say temperatures over the last year were 0.74 °C higher than the 1991–2020 average and 1.62 °C above the 1850–1900 pre-industrial average.

In Europe, last month’s temperature was 1.74 °C above the 1991–2020 September average, making it Europe’s second-warmest September after 2023, when temperatures were 2.51 °C above normal. Like the rest of the world, Europe saw above-average rainfall across much of the continent, according to the Daily Mail. Storm “Boris” brought heavy rain, flooding, and related destruction to Central and Eastern Europe in the middle of the month.

Outside Europe, temperatures ran above normal in Canada, the central and western United States, South America, northeastern Africa, China, and Japan. C3S also reported that the global average sea surface temperature in September reached 20.83 °C, the second-highest value on record after September 2023.