Weather Bee | July's sudden warming surge leads to the warmest day globally on record

The sharp reversal in the past week can be seen by comparing the averages for different periods of the month. The average warming in the month — from July 1 to any date up to July 17 — had hovered between 1.36°C to 1.39°C. This number has increased continuously from July 18 and the average warming for the month was 1.45°C on July 23, the latest day for which this data is available.

While the average warming in July so far is below the level seen last year at this time (average warming of 1.53°C on July 23), the sharp rise in warming in the past week is a big departure from the trend seen in the 30 days before that. Warming had been steady and below the 1.5°C mark every day from June 18 to July 17. This 30-day streak was the longest since June 6 last year, and a break from the trends seen in the past year. The second-longest streak after June 6 last year was a 22-day streak that ended on July 2, 2023. Between August 20, 2023, and May 4, 2024, no streak of under 1.5°C warming had been longer than four days. This suggested that warming in global temperatures may be moderating after the end of El Niño, a periodic warming of the equatorial Pacific Ocean that adds to global temperatures. That may not necessarily be the case.

Chart 1

This increase in warming seen in the past week has also made another temperature record. There is now a new record for the top three warmest days recorded on Earth. The average global temperatures recorded from July 21 to July 23 – 17.09°C, 17.16°C, and 17.15°C — are now the three highest daily temperatures recorded on Earth. This record was held previously by the average temperatures for July 6 (17.08°C), July 7 (17.07°C), and July 5 (17.06°C) in 2023.

To be sure, at least so far, the record for the warmest day is not held by a day when the daily temperature warmed up the most compared to the pre-industrial average. The temperature on July 22 was 1.697°C warmer than the pre-industrial average. While this is a very high level of warming, it is ranked “only” 146th highest in history. The reason July 22 temperature became the warmest on record despite this is that even the pre-industrial average for July 22 is high. This is because July is a summer month in the northern hemisphere and the late June-early August period usually sees the peak of global temperatures in absolute terms. The global average of temperature follows the trends of the northern hemisphere because this is where most of the land on Earth is. Since land warms and cools down faster than water, temperature variations over land drive global temperature variations.

Chart 2

This brings us to the most important question. What led to the change in the warming trends this past week? It is not possible to analyse this independently right now, because the detailed ERA5 data, whose averages were used for this analysis, comes with a lag. The data for the period after July 18 will only become available in the coming days. However, a Copernicus Climate Change Service (C3S) statement has suggested that the sudden spike in warming may be related to high levels of warming over large parts of Antarctica. Warming over Antarctica has been very high in recent years partly because of the effects of global warming. As the Earth warms up, it decreases the extent of ice at the poles. This allows the polar regions to warm up faster because ice reflects sunlight and helps in keeping temperatures cool. As the region warms up because of a lack of ice, it melts even more ice, pushing it into a vicious cycle.

Read together, these trends highlight how unpredictable global weather has become due to the unforeseen levels of warming being recorded since last year. While the end of El Niño might have stopped the additional heat being pumped out from the seas, it was not enough to keep global warming below the 1.5°C mark for more than 30 days.

Abhishek Jha, HT’s assistant editor-data, 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.