'Astonishing' global temperatures in January 2025 surprised scientists

Last month set a new record for the hottest January ever documented, surprising climate experts who had expected that a developing La Niña would finally start easing a prolonged bout of unusual heat.

According to the Copernicus Climate Change Service, January 2025 was 1.75°C warmer than in pre-industrial times, continuing a notable series of high-temperature records spanning 2023 and 2024. 

Human-generated greenhouse gas emissions have largely driven this persistent warming trend.

A weaker La Niña than anticipated

Most climate scientists anticipated that the exceptional heat wave would lose momentum once an El Niño event – peaking in January 2024 – gave way to La Niña, which typically brings a temporary cooling effect. 

Yet temperatures have remained at, or near, record-breaking levels, prompting discussion about additional factors that may be elevating global warmth beyond forecasts.

Researchers caution that even slight increments in global temperature magnify both the intensity and frequency of extreme weather phenomena such as heatwaves, severe rainfall, and drought.

Concerning jump in January heat

January exceeded the previous monthly record (set in January 2024) by 0.09°C, a margin that Copernicus climate scientist Julien Nicolas described as “sizeable” in the context of global temperature shifts. 

“This is what makes it a bit of a surprise…you’re not seeing this cooling effect, or temporary brake at least, on the global temperature that we were expecting to see,” said Nicolas.

Stefan Rahmstorf from the University of Potsdam pointed out that this is the first time in recorded data that a La Niña phase has yielded temperatures higher than those during the preceding El Niño. 

“This is of serious concern – over the past sixty years, all twenty five La Niña January’s have been cooler than surrounding years,” said Rahmstorf.

This year’s La Niña is predicted to be mild, and Copernicus reported evidence that surface temperatures in parts of the equatorial Pacific may be slowing or stalling the expected move toward cooler conditions. Nicolas noted that the phenomenon could vanish entirely by March.

Surpassing the Paris Agreement goal

Last month, Copernicus announced that the average global temperature for 2023 and 2024 had, for the first time, surpassed 1.5°C above pre-industrial levels. 

Though this does not confirm a permanent breach of the long-term Paris Agreement goal of limiting warming to 1.5°C, it does reveal that the threshold is being tested.

Overall, scientists do not anticipate 2025 to eclipse 2023 and 2024’s record-breaking heat; they predict it will probably rank as the third-warmest year. 

Nonetheless, Copernicus plans to carefully track ocean temperatures in 2025 to learn more about the planet’s evolving climate conditions.

The role of oceans in climate change

Oceans function as a crucial moderator of Earth’s climate and a major carbon sink. Cooler sea waters are able to capture more heat from the air, thereby contributing to reduced atmospheric temperatures. 

Cooler oceans also hold on to around 90 percent of the extra heat produced by the burning of fossil fuels.

“This heat is bound to resurface periodically,” Nicolas said. “I think that’s also one of the questions – is this what has been happening over the past couple of years?”

Astonishing heat in January

Sea surface temperatures have reached notably high levels throughout 2023 and 2024; in January alone, they were the second warmest ever recorded. “That is the thing that is a little puzzling – why they remain so warm,” Nicolas added.

University College London climate researcher Bill McGuire described it as “astonishing and frankly terrifying” that January remained near record highs even after La Niña conditions emerged. 

Meanwhile, Joel Hirschi from the UK’s National Oceanography Center advised restraint when interpreting only one month’s data, remarking that peaks had also been noted after past El Niño phases, even with La Niña underway.

Explanations for record heat 

Scientists generally concur that the long-term rise in global temperatures is primarily caused by burning fossil fuels, though natural climate cycles can influence yearly temperature variations. 

Still, experts say that El Niño alone cannot explain what has transpired in the atmosphere and oceans, meaning other explanations are being explored.

One possibility is that the move toward cleaner shipping fuels that began in 2020 has accelerated warming by curtailing sulfur-based emissions that help form sunlight-reflecting clouds. 

Another study, published in December, questioned whether fewer low-altitude clouds might be letting more heat reach Earth’s surface.

“These are avenues that must be taken seriously, and remain open,” said Robert Vautard, a top researcher with the UN’s Intergovernmental Panel on Climate Change.

Hottest Earth in 125,000 years

Copernicus harnesses billions of measurements from satellites, ships, planes, and weather stations to form its climate estimates. 

Though the agency’s own records trace back to 1940, other climate data sources – like ice cores, tree rings, and coral skeletons – enable scientists to extrapolate findings from a much deeper past.

Based on that broader array of evidence, researchers believe that the current period could well be the hottest Earth has experienced for at least 125,000 years.

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