GISTEMP data shows that February 2024 was 1.44°C warmer than the 1951-1980 average of global February temperature, making February 2024 the warmest in GISTEMP’s record.

Since February also marks the end of the boreal (or northern hemisphere) winter that starts in December, February’s data effectively also shows that the 2023-2024 boreal winter was the warmest on record. The 2023-24 boreal winter was 1.34°C warmer than the 1951-1980 average.

Even casual observers of global climate might notice that the GISTEMP data cited above does not tell us deviation from pre-industrial averages, which is the basis for the global warming targets of 1.5°C and 2°C. The reason why NASA does not report this is that its estimates only start from 1880. The pre-industrial average is usually taken as the average for the 1850-1900 period.

However, given the sparse temperature records in the pre-industrial period, NASA's is not the only dataset that does not have the 1850-1900 average. Scientists use different approximations to solve this problem. One such approximation is using the HADCRUT5 (Hadley Centre/Climatic Research Unit Temperature) averages for the 1850-1900 period to calculate deviations relative to that period.

Using HADCRUT5 data to adjust GISTEMP shows that February 2024 was 1.76°C warmer than the 1850-1900 average, the sixth consecutive month that was at least 1.5°C warmer than the 1850-1900 average. Even this is not a completely new trend. Earlier, GISTEMP monthly averages crossed the 1.5°C threshold in four consecutive months starting December 2015, and the three consecutive months starting December 2019 and March 2023.

What is more alarming about the February update is that the 12-month running mean of GISTEMP has also gone above the 1.5°C threshold at the end of February. In other words, the year-ending February 2024 was the first year-long period when the 1.5°C threshold was breached in GISTEMP. This had never happened earlier.

Chart: Deviation of monthly global mean temperature in GISTEMP

To be sure, as HT explained earlier, even the average for a whole year crossing the 1.5°C threshold does not mean that the Paris Agreement’s goal has been breached. That must happen for temperatures aggregated over longer time periods, such as a decade.

However, for the average for a decade to cross the 1.5°C threshold, at least one year needs to cross that threshold. The first of those years can now be said to have taken place, as more and more datasets show that the threshold is being breached. The 12-month running mean of global warming relative to the pre-industrial average has crossed the 1.5°C threshold in three of five prominent estimates so far: Berkeley Earth (first time in December), ERA5 of C3S (first time in January), and NASA’s GISTEMP (first time in February).

To be sure, it is likely that HADCRUT5 will also cross this threshold in February when its February data is released. HADCRUT5’s 12-month running mean had reached 1.49°C warming in January. Since the two datasets, GISTEMP and ERA5, show the 12-month running mean increasing in February compared to January, HADCRUT5 is also likely to do so. This is because the general trend of warming is similar in most datasets even if the numbers they report differ depending on the approximations used.

Abhishek Jha, HT’s senior data journalist, analyses one big weather trend in the context of the ongoing climate crisis every week, using weather data from ground and satellite observations spanning decades.