2025 was not the warmest year on record. Read the three-year average instead
WMO puts 2025 at 1.44°C above pre-industrial, second or third warmest depending on the dataset. The 2023–2025 mean of 1.48°C is the figure that describes exposure.
The World Meteorological Organization released its consolidated global temperature figures for 2025 yesterday, and the headline is a rare one in recent years: the number went down.
The global average surface temperature for 2025 was 1.44°C above the 1850–1900 baseline, with an uncertainty of ±0.13°C [s1]. Of the eight datasets WMO consolidates, two ranked 2025 as the second warmest year in the 176-year record and six ranked it third [s1].
For a health readership, the useful move is to ignore the ranking entirely.
Why the ranking is the least informative part
Year-to-year position in a list is heavily influenced by the El Niño–La Niña cycle, which redistributes heat between ocean and atmosphere. It reports the phase of a natural oscillation, not the trajectory of exposure.
WMO Secretary-General Celeste Saulo made the point directly: 2025 started and ended with a cooling La Niña and was still one of the warmest years on record globally, because of the accumulation of heat-trapping greenhouse gases in the atmosphere [s1].
A cooling phase producing the second or third warmest year in 176 years is a statement about the baseline, not about 2025.
The number that describes exposure
Two figures in the release carry more information than the ranking.
The first is the three-year mean. Averaged across 2023 to 2025, global temperature ran 1.48°C above pre-industrial, with the same ±0.13°C uncertainty [s1]. A multi-year average smooths out the El Niño signal and is therefore closer to what a population actually experiences as a sustained condition.
The second is the streak. All eight datasets agree that the past 11 years — 2015 through 2025 — were the warmest on record [s1].
Eleven consecutive years is not a run of unusual weather. It is the description of a different climate, and it is the timescale on which health systems accumulate the exposures that matter: repeated summer heat episodes rather than one exceptional event, and chronic rather than acute adaptation demands.
The distinction has practical consequences. A single record summer is a surge event — health services absorb it, mortality spikes, and the system returns to baseline. A sustained shift in the distribution is a capacity problem: it changes how buildings need to be built, how occupational limits are set, and how many days a year a given population spends above the threshold at which its most vulnerable members are at risk. The first is managed with an emergency plan. The second requires infrastructure that takes decades to build.
Which of those two a health system is facing is a question the annual ranking cannot answer and the eleven-year streak can.
What ocean heat adds
WMO also reports that ocean heating continues unabated [s1].
Ocean heat content is the least visible of these indicators and the slowest to reverse. That WMO reports it as continuing unabated in a La Niña-influenced year [s1] is the clearest available signal that the underlying accumulation is not tracking the annual headline.
The connection WMO draws
The release links elevated temperatures to extreme weather events including heatwaves, intense rainfall and tropical cyclones, and emphasises the importance of early warning systems [s1].
That framing is worth taking literally rather than rhetorically. The health burden of a heatwave is heavily modified by whether people know it is coming, whether cooling is reachable, and whether health services have pre-positioned. Those are the variables an early warning system moves. The temperature itself is not modifiable on the timescale of a warning; the response is.
What the figure does not tell you
A global mean anomaly is an average over a planet, and no one lives at the global mean. Heat exposure is distributed by latitude, by urban form, by housing quality, by occupation and by age, and the same 1.44°C corresponds to very different local conditions and very different mortality risks.
The global figure is a tracking number for the forcing. It is not, on its own, a health statistic, and it should not be read as one.
What to watch
The three-year average is the line to follow. WMO reports it alongside the annual figure precisely because the annual figure oscillates [s1]. Whether the multi-year mean continues to climb through a La Niña-influenced period is the question that distinguishes a trend from a peak.
Sources
- [s1] WMO confirms 2025 was one of warmest years on record. World Meteorological Organization, 14 January 2026. https://wmo.int/media/news/wmo-confirms-2025-was-one-of-warmest-years-record
Sources
- WMO confirms 2025 was one of warmest years on record — World Meteorological Organization , January 14, 2026
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