For the second year in a row, Mediterranean Sea temperatures are reaching record levels, threatening fish and marine plants, promoting invasive species and increasing the potential intensity of rainfall in a region particularly affected by the effects of global warming.
On August 11, the daily median temperature of the Mediterranean Sea surface reached 28.67 °C, close to the record of 28.71 °C measured on July 24, 2023, said Justino Martinez, a researcher at the Institute of Marine Sciences (ICM) in Barcelona and the Catalan institute ICATMAR.
These preliminary surveys come from satellite data from the European Copernicus Observatory, which go back to 1982.
For two successive summers, the Mediterranean will have been warmer than during the exceptionally hot summer of 2003, when a daily median of 28.25°C was measured on 23 August, a previous record which had stood for twenty years.
Today, “what is remarkable is not so much reaching a maximum on a given day, but observing a long period of such high temperatures, even without breaking a record,” commented Justino Martinez.
“Since 2022, surface temperatures have been abnormally high over a long period, even when we take into account the context of climate change,” he added.
The record level of 2023 is however reached this year “more than fifteen days later and usually the surface temperatures drop from the end of August”, the scientist tempers.
Locally, water temperatures above 30°C have been recorded since the beginning of August, notably on a buoy off Monaco, another in Corsica, and near Valencia in Spain. “Boiling sea in Campania”, the region of Naples, is the headline in the daily newspaper La Repubblica on Tuesday.
The Mediterranean region, hit in July, as in 2023, by several heatwaves and violent forest fires in Greece, has long been classified as a “hotspot” of climate change by the United Nations Intergovernmental Panel on Climate Change (IPCC).
Blue Crabs and Fire Worms
“Since the 1980s, a drastic change has taken place in Mediterranean marine ecosystems, with both a decline in biodiversity and the arrival of invasive species,” says the IPCC.
During the marine heatwaves between 2015 and 2019 in the Mediterranean, around fifty species (corals, gorgonians, sea urchins, molluscs, bivalves, posidonia, etc.) experienced mass mortality between the surface and 45 meters deep, according to a study published in July 2022 in the journal Global Change Biology.
Exotic tropical species are taking advantage of rising temperatures, such as the blue crab that is devastating shellfish farms in the Po Delta in northern Italy.
In Sicily and Calabria, fishermen are seeing an increase in their nets of fish devoured by fireworms, voracious predators also favoured by the heat of the water.
The average temperature of the Mediterranean has increased by about 1.2 degrees over the past 40 years, according to Federico Betti, an expert on invasive species at the University of Genoa.
Under a scenario of global warming of more than 1.5°C since pre-industrial times, 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, IPCC experts warn. On average, the world is already estimated to be about 1.2°C warmer.
In Nice, the water has been 3 or 4 degrees above normal since July 15, which prevents the air from cooling at night and leaves the population without respite between two often scorching days.
Furthermore, “an abnormally high temperature of the Mediterranean Sea in autumn can make Mediterranean episodes more intense by allowing the atmosphere to store more humidity on its way to the coasts”, but without however causing the occurrence of these devastating rain phenomena, recalls Météo-France.
Heat wave in Antarctica
Antarctica, the coldest continent on the planet, is also experiencing a heatwave during its winter, of exceptionally long duration, according to the British institute specializing in the study of polar regions.
“The duration of this warm spell is unusual,” Thomas Caton Harrison, an expert at the British Antarctic Survey, told AFP.
In July, average temperatures on the southern continent were 3.1 degrees Celsius above seasonal norms, he said. That made it the second warmest July — after July 1981 — since records began in 1979.
Average daily temperatures ranged from -34.68°C on July 15 to -28.12°C on July 31, according to data posted online by the University of Maine. The average temperature across the continent was -26.6°C on August 7, the latest date available.
The anomaly even reached +9 to +10°C in July over a limited region that includes Queen Maud Land and part of the Weddell Sea.
Temperature anomalies are common during the Antarctic winter, but this episode is unusual in its duration, scientists say. It is the prolonged warmth that is “remarkable,” insists Thomas Caton Harrison.
“Very preliminary data suggest that we may be on track for an exceptionally warm Antarctic winter,” he said.
The windswept white continent with no permanent population is the coldest place on Earth. But it is also affected by global warming.
In a study published in June in the journal Nature Geoscience, researchers estimated that a new “tipping point” could be about to be crossed, with Antarctica heading toward “uncontrolled melting” of its ice sheets due to now warmer ocean water.
This poses a risk of rising sea levels as accelerated melting outpaces the formation of new ice on the continent, threatening coastal populations around the world.