The world warmed to yet another monthly heat record in January, despite an abnormally chilly United States, a cooling La Nina and predictions of a slightly less hot 2025, according to 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.

January 2025 globally was 0.09 degrees Celsius (0.16 degrees Fahrenheit) warmer than January 2024, the previous hottest January, and was 1.75 C (3.15 F) 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 Celsius (2.7 Fahrenheit) 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 U.S. 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 civilization.

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 Nino and global temperatures tend to spike. Last year was a substantial El Nino, though it ended last June and the year was even warmer than initially expected, the hottest on record.

El Nino's cooler flip side, a La Nina, tends to dampen the effects of global warming, making record temperatures far less likely. A La Nina 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 Nina 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 Nino like last year, temperatures fall rapidly, but "we've not seen that," Burgess told The Associated Press.

For Americans, news of a record warm January might seem odd given how cold it was. But the U.S. is just a tiny fraction of the planet's surface, and "a much larger area of the planet's surface was much, much warmer than average," Burgess said.

January was unseasonably mild in the Arctic. Parts of the Canadian Arctic had temperatures 54 degrees Fahrneheit warmer than average and temperatures got so warm sea ice started melting in places, Burgess said.

Copernicus said the Arctic this month tied the January record for lowest sea ice. The U.S.-based National Snow and Ice Data Center had it as second-lowest, behind 2018.

February has already started cooler than last year, Burgess said.

But 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 Nino variations and expected climate change since 2020, Hansen said. He noted recent shipping regulations that have resulted in reduced sulfur 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 temperature increases are still within what climate models forecast.

Source