Weather Bee: Will 2025 be another year of 1.5°C warming?
The average so far does suggest this as a possibility, but the probability of this happening will become clearer later in the year. Here is why.
There is good reason for asking this question. Of the six global temperature datasets tracked by the World Meteorological Organization (WMO), five have published their data up to March for 2025. Despite the cooling effect of a La Nina, a cyclical cooling in equatorial Pacific that cools global average temperature, all five average more than 1.5°C warming relative to the pre-industrial average so far. Does this mean that 2025 will be another year of 1.5°C warming after 2024? The average so far does suggest this as a possibility, but the probability of this happening will become clearer later in the year. Here is why.
The WMO tracks six global temperature datasets. These are the datasets published by National Oceanic and Atmospheric Administration (NOAA), Japan Meteorological Agency (JMA), UK’s Met Office Hadley Centre, National Aeronautics and Space Administration (NASA) of the US government, Copernicus Climate Change Service (C3S) of the European Centre for Medium-Range Weather Forecasts (ECMWF), and Berkeley Earth, which is a US-based non-profit. All except NOAA’s dataset – which generally shows a lower level of warming than the rest – showed warming in 2024 as more than 1.5°C. This made 2024 the first year when there was more than 1.5°C warming in multiple datasets. This had happened only in Berkeley Earth’s data in 2023, a dataset that generally shows a higher level of warming than the others. The 2015 Paris Agreement asked for long-term warming to be kept under 1.5°C.
Of the six organisations listed above, all except the Met Office have also published their updates for 2025 up to March. All five show more than 1.5°C warming in 2025 on average in the first three months of the year. Moreover, C3S, whose ERA5 data is updated daily with a two-day lag, shows 1.5°C warming even in the April so far. However, this does not necessarily indicate that 2025 is headed towards 1.5°C warming, although that is a possibility.
Two reasons for optimism about the expected level of warming in 2025 are somewhat statistical. While the year up to March is has shown 1.5°C warming, and second warmest January-March period in all but Berkeley Earth’s data (where the period is ranked third warmest), the average warming this year is closer to 2016 levels than 2024. 2016 experienced one of three warmest January-March periods along with 2024 and 2025, but ended up with less than 1.5°C warming in all datasets.
Another statistical reason for optimism is that warming was generally higher in non-summer months of the northern hemisphere (June-August) in the past 10 years. This means that the next few months might climb down from the level of warming seen so far in the year.
To be sure, both past statistics and forecasts for the rest of the year do not rule out the possibility of 1.5°C warming at the end of the year. For example, 2023 started with less than 1.5°C warming, but warmed up late in the year (partly because of an El Nino, which has a warming effect on global temperatures) to end up as the second warmest year in most datasets and close or above the 1.5°C threshold.
Late warming, such as in 2023, cannot be ruled out this year, either. While La Nina and neutral conditions (neither El Nino nor La Nina) have relatively higher probability in forecasts for the second half of the year, El Nino also has a significant probability close to 20%. Since forecasts for these events in the Pacific are less certain at this time of the year – the picture clears up around northern hemisphere’s summer – so is the outlook for the post-summer months.
These trends read together mean that although the first quarter of 2024 has shown more than 1.5°C warming, the warming outlook for the year on average is somewhat uncertain right now. If the Pacific’s conditions turn La Nina again at the end of the year, it will certainly help in keeping 2025 under 1.5°C warming, with the first three months trending closer to 2016 than 2024 on average. If the Pacific is headed towards El Nino towards the end of the year, we might get back-to-back years of 1.5°C warming.