An emerging “La Nina” weather pattern that cools global temperatures was not enough to prevent last month from becoming the hottest January on record, scientists have said.
January 2025 was 0.79°C above the 1991-2020 global average for the month and 1.75°C above pre-industrial levels, scientists from the EU’s Copernicus Climate Change Service (C3S) said. It extends a persistent run of record highs over 2023 and 2024, as human-caused greenhouse gas emissions crank up the global thermostat.
It makes it the 18th month in the past 19 for which average global air surface temperatures were more than 1.5°C above what they were before the industrial era.
Climate scientists had expected this exceptional spell to subside after a warming El Nino event peaked in January 2024 and conditions gradually shifted to a cooling La Nina phase.
But the heat has lingered at record or near-record levels since, sparking debate among scientists about which other factors could be driving global warming to the top end of expectations.
"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 Julien Nicolas, a climate scientist from Copernicus.
Weak cooling effect
La Nina is expected to be weak and Copernicus said prevailing temperatures in parts of the equatorial Pacific Ocean suggested "a slowing or stalling of the move towards" the cooling phenomenon.
Mr Nicolas said it could disappear completely by March.
Overall, it means 2025 is not expected to follow the previous two years into the history books: scientists predict it will be the third-hottest year since records began.
Scientists warn that every fraction of a degree of warming above the 1.5°C threshold increases the intensity and frequency of extreme weather such as heatwaves, heavy rain and drought.
The analysis, using billions of measurements from satellites, ships, aircraft and weather stations around the world, also found the 12-month period from February 2024 to January 2025 was 1.61°C above the estimated temperature for 1850-1900, which is used to define the pre-industrial era.
The record highs come despite the emergence of La Nina pattern in the Pacific, which temporarily cools global temperatures.
The data shows sea-surface temperatures outside the polar regions averaged 20.78°C, making it the second-hottest January after last year’s record.
Temperatures were below average in the central Pacific but close to or above average in the eastern Pacific – suggesting a slowing or stalling of the move to La Nina conditions, while surface temperatures were unusually high in many other oceans and seas.
The average temperature over land in Europe was 1.8°C, which is 2.51°C above the 1991-2020 average for January, making it the second-warmest January for the continent after 2020.
While temperatures were mostly above average over southern and eastern Europe, they were below average in the UK and Ireland, Iceland, northern France and northern Scandinavia.
Samantha Burgess, strategic lead for climate at the European Centre for Medium-Range Weather Forecasts, which runs C3S, said: “January 2025 is another surprising month, continuing the record temperatures observed throughout the last two years, despite the development of La Nina conditions in the tropical Pacific and their temporary cooling effect on global temperatures.
“Copernicus will continue to closely monitor ocean temperatures and their influence on our evolving climate throughout 2025.”
