Weather Bee | January 2025 all set to be the warmest January month on record

ERA5 data is not the only global temperature dataset. The World Meteorological Organization tracks six global temperature datasets, for example. However, the daily ERA5 data has a lag of just two days, which allows one to get an early estimate of global temperature trends from this dataset.

The data from ERA5 for January 2025 are available up to January 28. This shows that the average warming in the month relative to the pre-industrial average is 1.75°C, the highest ever for this part of the month. The previous record for the highest global temperature for the first 28 days of January was held by January 2024, which was 1.63°C warmer than the pre-industrial average.

Daily data shows that only four dates in January this year were cooler than January 2024 (January 1-2 and January 27-28). It is largely the middle part of the month that has made January 2025 shoot past the warming seen last year. Given the high warming in the middle of the month, it is not likely that warming in January this year will fall behind last year’s level although the temperatures have converged towards the end of the month. The difference between the warming for January taken in its entirety and the warming for the first 28 days of January in the past 10 years has been at most 0.02°C. In comparison, the month so far is warmer than the first 28 days of January 2024 by 0.12°C.

Given the trends described above, and the fact that data for only four days needs to be finalized, it is even less likely that January 2025 will show less than 1.5°C warming. This means that this will be the fourth January month when warming in global temperature is at least 1.5°C. This will also make January 2025 the sixth consecutive month when warming has been more than 1.5°C.

What do the trends seen in January mean? One: They are in line with the UK Met Office's forecast that 2025 is likely to be among the three warmest years on record, along with 2024 and 2023, which hold the record for the two warmest years so far.

Secondly, the January trends also mean that La Nina (a cyclical cooling of the equatorial Pacific that has a cooling impact on global temperatures) that started in mid-December is yet to have an impact on air temperatures (or what is simply known as temperature).

To be sure, temperatures in the Pacific are expected to have an impact on air temperatures only with a 2-4 month lag (this was discussed in detail here). However, there is still reason to worry about January temperatures. El Nino (cyclical warming in the equatorial Pacific that gives a bump to air temperatures) ended in April 2024. That global average temperature continues to reach record or near-record levels even eight months after El Nino suggests that sea temperatures explain only a fraction of the warming we are seeing currently. This means that the final conclusion one can draw from January temperatures is that the level of long-term warming is high enough now to negate the impact of cyclical factors.