January has surprised climate scientists by setting a new global temperature record, in an early indication that 2025 could see more severe warming than first thought.
It was the hottest January on record at 1.75掳C above the 1850 to 1900 average, beating the previous record set a year earlier, when temperatures were 1.7掳C above pre-industrial levels.
It is a surprise start to a year when global temperatures were expected to start falling. 2023 and 2024 were exceptionally warm years, with last year confirmed as the hottest in human history. Each month from January to June 2024 was warmer than the corresponding month in any previous year on record.
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2025 was expected to have marginally cooler temperatures thanks to the emergence of a La Ni帽a climate pattern in the Pacific Ocean in late 2024. But early data suggests this isn鈥檛 the case, according to , a climate scientist at US software firm Stripe.
鈥淲e鈥檇 generally expect global temperatures to fall the following year as El Ni帽o fades, particularly when modest La Ni帽a conditions develop,鈥� says Hausfather. 鈥淭hat鈥檚 the reason it is so surprising to see a new record this January compared with last January.鈥�
His analysis, published on the science blog is based on daily data from the Copernicus ERA5 temperature record. Copernicus, the European Union鈥檚 climate service, will be publishing its own monthly analysis in the coming week.
at the Met Office, the UK鈥檚 national weather service, says the high temperatures seen in January are 鈥渦nusual鈥� and run counter to what he would have expected for this year. It could be down to a range of factors, he says, including variable atmospheric conditions, a reduction in aerosol pollution and lingering water vapour in the atmosphere from the 2022 Hunga Tonga-Hunga Ha鈥檃pai volcanic eruption. A decline in cloud cover over oceans, which could be a feedback effect of warming, is also a 鈥渨orrying possibility鈥�, says Scaife.
But he cautioned against reading too much into one month of data. 鈥淭his is a wiggle,鈥� he says. 鈥淟et鈥檚 see what happens in the next few months.鈥� The Met Office鈥檚 prediction that 2025 is likely to be slightly cooler than 2024 still stands, he adds.
Warm temperatures may have persisted following the end of El Ni帽o because the oceans are warming at an accelerating rate, says at the University of Reading, UK. Research published last month indicates that the rate of ocean warming has quadrupled since 1985.
鈥淎side from a cooler-than-average band along the equator in the eastern Pacific due to the La Ni帽a conditions, the rest of the sea surface remains remarkably warm,鈥� says Allan. 鈥淎lthough the swing from moderate El Ni帽o to a weak La Ni帽a is having a small cooling effect on the surface of the ocean, heat continues to flood into the climate system as atmospheric greenhouse gases continue to rise and the reflective haze of aerosol particle pollution diminishes in some regions following clean air regulation.鈥�
Worryingly, concentrations of carbon dioxide in the atmosphere are also increasing at an accelerated rate. This may mean the world鈥檚 forests, swamps and other carbon-storing landscapes are losing their ability to absorb carbon as the world warms, says Allan.
The final week of January 2025 saw global temperatures drop below 2024 levels, and temperatures are expected to fall further into February as the northern hemisphere sharply cools. This makes it less likely that February will also set a new record, Hausfather wrote. But given the record warmth of January, he warned that 2025 could be hotter than predictions suggest.
