Record Heat in the Mediterranean Could Have Devastating Consequences for Ecosystems

Sea surface temperatures in the Mediterranean have reached their highest level ever recorded for June. According to data collected by the European Union’s (EU) Copernicus Climate Change Service (C3S) and analysed by Meteo-France, sea surface temperatures reached 26.01 degrees Celsius on June 29. Overall temperatures are currently running 3 degrees Celsius above average, with some places along the coasts of France and Spain experiencing increases exceeding 4 degrees Celsius.

The most intense warming has been observed in the western Mediterranean Basin, including the Balearic and Tyrrhenian Seas. Given current weather conditions, scientists say temperatures are unlikely to drop any time soon.

The Region Could Change Beyond Recognition

The Mediterranean is considered one of the world’s most vulnerable “climate change hotspots” , warming much faster than the global average. Experts warn that marine heatwaves – long periods when ocean temperatures are abnormally high – could change the region beyond recognition unless action is taken to curb climate change.

A persistent and growing marine heatwave is gripping the region, with “severe” and “extreme” conditions emerging off the coast of southeastern Spain and northern Morocco.

Marine scientists warn that the resulting situation could have devastating effects on biodiversity, fisheries, aquaculture and even weather in southern Europe and north Africa.

Coral Populations Have Already Declined by 90%

“Marine heatwaves of this magnitude in the Mediterranean have had major impacts on marine life,” said Dr Kathryn Smith, of the UK’s Marine Biological Association. “We have seen mass mortality of invertebrate species, die-offs in seagrass beds and disease outbreaks in mussel farms in the past. We are likely to see similar impacts from this event.”

These events have already reduced coral populations by 90% and pushed the fan mussel to the brink of extinction. Warmer waters hold less oxygen, leading to mass fish kills, as seen in Tuscany in 2024. As fish dive deeper to escape the heat at the surface, they are out of reach of seabirds, which are dying en masse.

Warm Seas Fuel Extreme Weather

The effects of marine heatwaves also spread to land. Warmer seas fuel extreme weather, as seen in Storm Daniel, which killed an estimated 6,000 people in 2023. This storm is 50 times more likely and 50% more severe due to higher sea surface temperatures in the Mediterranean.

Floods in Valencia in 2024, which killed more than 200 people, were also partly linked to higher sea surface temperatures. Marine heatwaves are now 10 times more intense and three times longer than in the pre-industrial era.

“Responsible Climate Change”

“Climate change is responsible for the global increase in the frequency, duration and intensity of marine heatwaves,” said Dr Alistair Hobday, research director of the Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) Sustainable Marine Future Programme.

The Mediterranean has been warming steadily since the 1980s and has accelerated sharply in the last 10 years. Over the last 40 years, there has been an average of four heat waves per year covering almost the entire sea, compared to one marine heat wave per year in defined areas. Temperatures have been consistently above average for the last five years.

“The widespread heatwave emerging in the western Mediterranean now requires close attention,” warned Dr. Karina von Schuckmann, senior advisor at Mercator Ocean International.

Scientists stress that this trend can only be stopped with rapid global emissions cuts. Without urgent action, this climate hotspot could become a permanent phenomenon.