The Mediterranean Sea broke its daily temperature record

Europe 1 with AFP / Photo credit: Amaury Cornu / Hans Lucas / Hans Lucas via AFP 19:52 p.m., July 25, 2023

The waters of the Mediterranean Sea experienced Monday their highest known daily temperature, announced Tuesday to AFP the main Spanish maritime research center, in the middle of an exceptional heat wave over a large part of the Mediterranean basin, one of the "hot spots" of global warming. "A new record over the period 1982-2023 has been broken for the daily median sea surface temperature in the Mediterranean with 28.71 degrees," said researchers from the Institute of Marine Sciences (ICM) in Barcelona, analyzing satellite data from the European Copernicus observatory.

The previous record of 28.25 degrees was set on August 23, 2003. These data have yet to be confirmed by Copernicus, but "we are convinced that the median will not be very biased and that the indication of the temperature up to the first decimal place is generally correct," said researchers Justino Martinez and Emilio Garcia, joined by AFP. These scientists prefer the median temperature rather than the average (28.40 degrees Monday) because it is less "disturbed by atypical values", that is to say by extreme temperature readings in isolated points of the Mediterranean, they added.

More than 30 degrees locally

Locally waters of more than 30 degrees were recorded (4 degrees above normal) between Sicily and Naples. Such temperatures threaten marine ecosystems. During the 2015-2019 heat waves in the Mediterranean, about fifty species (corals, gorgonians, sea urchins, molluscs, bivalves, posidonia, etc.) experienced massive mortalities between the surface and 45 meters deep, according to a study published in July 2022 in the journal Global Change Biology.

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The Mediterranean region, hit in July by sometimes record temperatures and violent forest fires in Greece, has long been classified as a climate change "hotspot" by the United Nations' Intergovernmental Panel on Climate Change (IPCC). "Since the 80s, a drastic change has taken place within Mediterranean marine ecosystems, with both a decline in biodiversity and the arrival of invasive species," says the IPCC.

Species threatened with extinction

In the scenario of global warming of more than 1.5 degrees since the pre-industrial era, more than 20% of fish and invertebrates exploited in the eastern Mediterranean could disappear locally by 2060 and fishing revenues could decline by up to 30% by 2050, warn these experts. On average, the world is already at about +1.2 degrees.

If the temperature of Mediterranean waters is increasing tendentially, "there is no clear evidence, statistically speaking, of an increase in the frequency of marine heat waves for the Mediterranean basin over the period" 1982-2023, note however the Spanish researchers of the ICM. "It is estimated that the origin of marine heatwaves is mainly – but not only – atmospheric... This is a topic under debate, but if it is, only a mitigation of atmospheric heatwaves will lead to attenuation of marine heatwaves," they comment.