January 2025 was likely the warmest January month on record with an average monthly temperature anomaly of 1.75°C above the pre-industrial (1850-1900) average for the month, according to data from the ERA5 dataset analysed by climate scientists.
The record anomaly is also evidenced by the warmer-than-normal temperatures around the world in the past month, both in the northern (wintertime) and southern hemispheres (summertime).
As recent as on January 31, temperature records were broken in Jamaica in the northern hemisphere and Madagascar in the southern hemisphere, according to data collated and shared on social media platform X by weather historian M Herrera.
The ERA5 dataset is provided by the European Centre for Medium Range Weather Forecasting (ECMRWF) which also implements the Copernicus Climate Change Service (C3S) for the European Commission.
This unusual January warmth happened despite an ongoing La Nina phenomenon in the equatorial Pacific Ocean which generally leads to cooler-than-normal temperatures around the world. This was also the first time that January temperatures were much warmer-than-normal than the surrounding El Nino or neutral years.
“January 2025 was quite unexpectedly the warmest January on record at 1.75C above preindustrial, beating the prior record set in 2024,” wrote Zeke Hausfather, climate scientist at non-profit Berkeley Earth, on social media platform X.
“This is despite the presence of La Nina conditions in the tropical Pacific, with the El Nino event of 2023/2024 long faded,” he added.
The previous three record January months in 2024, 2020 and 2016 happened either during ongoing El Nino phenomenon like in 2024 and 2016 or when sea surface temperatures in the equatorial Pacific Ocean were approaching El Nino like in 2020.
El Nino is the warmer-than-normal phase of the El Nino Southern Oscillation (ENSO) phenomenon when generally global temperatures are warmer-than-normal.
The last El Nino phenomenon was declared by the World Meteorological Organization (WMO) in July 2023 and ended in June 2024.
This was a part of the reason for 2024 being the warmest year on record and crossing the annual average temperature anomaly of 1.5°C above the pre-industrial average. In fact, according to the WMO, the year was 1.55°C warmer than pre-industrial times.
The La Nina conditions began in December 2024, according to the National Oceanic and Atmospheric Administration (NOAA) of the United States and may continue through February to April 2025.
The NOAA expects it to be a short-lived La Nina unlike the three-year-long previous La Nina from 2020 to 2023, which had also witnessed extraordinary heat waves despite the temporary cooling that comes with the phenomenon.
The WMO had, in fact, warned in December 2024 that the fossil fuel led greenhouse gas (GHG) emissions fuelled warming may not relent in 2025, despite the La Nina. Earth’s natural climatic cycles such as the ENSO are increasingly being trumped and even slightly modified by GHG emissions caused warming.
With the ongoing La Nina phenomenon, climate scientists were expecting a cooler 2025. But the temperatures in January indicate that to not be the case.
“Both 2023 and 2024 were exceptionally warm years, at just below and above 1.5C relative to preindustrial in the WMO composite of surface temperature records, respectively,” wrote Hausfather on his website The Climate Brink.
“While we are still working to assess the full set of drivers of this warmth, it is clear that a sizable portion of 2024’s elevated temperatures were driven by a moderately strong El Niño event that peaked in November 2023. For this reason many of us expect that 2025 will be cooler than both 2023 and 2024, and is unlikely to be the warmest year in the instrumental record,” he added.
The world is in modest La Nina conditions that should, all things being equal, result in lower global temperatures, as per Hausfather. But he writes, “Global temperature over the past few months have exceeded or been at the upper end of what we’ve seen after any other El Nino event in the historical record.”
All January months with an ongoing La Nina have been cooler than their surrounding years with El Nino or ENSO neutral conditions, except for January 2025.
“An unexpected record (in January) to start things off may presage higher temperatures this year than many of us thought,” according to Hausfather.