Is global warming accelerating?

January 2025 sets new heat record globally, sparking debate among scientists on acceleration of global warming.

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 C 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 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.