January breaks another heat record despite hopes La Niña would slow global warming

The world warmed to yet another monthly heat record in January, leaving scientists shocked.

It was hoped that the La Niña weather which began in the same month would get 2025 off to a cooler start than 2023 and 2024, which broke heat records. But that did not happen, as confirmed by data from the European climate service Copernicus.

The surprising January heat record coincides with a new study by a climate science heavyweight, former top NASA scientist James Hansen, and others arguing that global warming is accelerating. It's a claim that's dividing the research community.

What is driving up global temperatures?

By far the biggest driver of record heat is greenhouse gas buildup from the burning of coal, oil and natural gas, but the natural contributions to temperature change have not been acting quite as expected, said Samantha Burgess, strategic lead for climate for the European weather agency.

The big natural factor in global temperatures is usually the natural cycle of changes in the equatorial Pacific Ocean waters. When the central Pacific is especially warm, it's an El Niño and global temperatures tend to spike. Last year was a substantial El Niño, though it ended last June and the year was even warmer than initially expected, the hottest on record.

El Niño's cooler flip side, a La Niña, tends to dampen the effects of global warming, making record temperatures far less likely. A La Niña started in January after brewing for months. Just last month, climate scientists were predicting that 2025 wouldn't be as hot as 2024 or 2023, with the La Niña a major reason.

“Even though the equatorial Pacific isn’t creating conditions that are warming for our global climate, we’re still seeing record temperatures,” Burgess said, adding much of that is because of record warmth in the rest of the world's oceans.

Usually after an El Niño like last year, temperatures fall rapidly, but “we've not seen that,” Burgess told The Associated Press.

How hot was January 2025?

January 2025 globally was 0.09 degrees Celsius warmer than January 2024, the previous hottest January, and was 1.75 C warmer than it was before industrial times, Copernicus calculated. It was the 18th month of the last 19 that the world hit or passed the internationally agreed upon warming limit of 1.5 C above pre-industrial times. Scientists won't regard the limit as breached unless and until global temperatures stay above it for 20 years.

Copernicus records date to 1940, but other US and British records go back to 1850, and scientists using proxies such as tree rings say this era is the warmest in about 120,000 years or since the start of human civilisation.

Will 2025 be the hottest year on record?

Don't count 2025 out in the race for hottest year, said Hansen, the former NASA scientist who has been called the godfather of climate science.

He's now at Columbia University. In a study in the journal Environment: Science and Policy for Sustainable Development, Hansen and colleagues said the last 15 years have warmed at about twice the rate of the previous 40 years.

“I'm confident that this higher rate will continue for at least several years,” Hansen told The Associated Press in an interview. “Over the full year it's going to be nip-and-tuck between 2024 and 2025.”

There’s been a noticeable temperature rise even when taking out El Niño variations and expected climate change since 2020, Hansen said. He noted recent shipping regulations that have resulted in reduced sulphur pollution, which reflects some sunlight away from Earth and effectively reduces warming. And that will continue, he said.

“The persistence of record warmth through 2023, 2024 and now into the first month of 2025 is jarring to say the least,” said University of Michigan environment dean Jonathan Overpeck, who wasn't part of the Hansen study. “There seems little doubt that global warming and the impacts of climate change are accelerating.”

But Princeton's Gabe Vecchi and University of Pennsylvania's Michael Mann said they don't agree with Hansen on acceleration. Vecchi said there's not enough data to show that this isn't random chance. Mann said that temperature increases are still within what climate models forecast.