We are in the middle of June and it doesn’t seem like it, but the western Mediterranean is burning. And no, it is not an exaggeration: we are talking about a marine heat wave with peaks of surface anomaly greater than 5 degrees in specific areas.
It is what experts call in technical jargon, a gigantic problem. Especially, facing autumn.
A ticking time bomb. The great temptation when we see this type of data is to plot a direct line between sea temperature in June and DANAs in October. But it would be a mistake. The mechanism exists, of course. However, the matter is a little more complex than we might think.
This is because the overheated sea is not a forecast of how much autumn rain we are going to suffer: it is a gauge of the ceiling of intensity that these rains can reach. The effect of an anomalously warm Mediterranean is to charge the atmosphere with water vapor and thus raise the amount of water that a DANA can precipitate.
But, and this is crucial, the trigger is atmospheric. It is useless to have a charged atmosphere without a mass of cold air at altitude that is detached from the general circulation.
What’s new? What is genuinely new is not that the Mediterranean is hot. It is, in fact, from 2022 on a sustained basis. What is new is that we have had a marine heat wave since May. That is, long before the historical calendar and still very far from the warmest moment (August).
Furthermore, whether we want to see it or not, El Niño is just around the corner and, although we hope not to receive its wildest impacts, the heat it will bring to the world makes experts very worried.
Why is it relevant? The data is clear. The Mediterranean basin heats up around 20% faster than the global ocean average and is trailing a streak of unprecedented records: 18 of the 20 highest daily values since 1982 were recorded between 2023 and 2024 (with a maximum of 28.15 °C on August 10, 2024).
The memory of the DANA of Valencia is still fresh and the certainty that the situation is getting worse It is a slab for the national climate conversation.
Are we going to get worse? It’s pure physics: a warmer sea increases evaporation and the water vapor content of the atmosphere (at a rate of 7% more vapor for each degree). The best example is Storm Daniel which, as the researchers showedit would have been much more unlikely without climate change.
That is why it is advisable to be precise and not take things out of context. The current scenario is problematic because if a DANA forms on the Mediterranean coast this autumn, it will have more fuel available to discharge more intense rains than with a cold sea. If it is not formed, nothing has to happen.
Image | Copernicus
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