The temperatures of the Mediterranean Sea in recent days have reached heat records set last summer, the main Spanish maritime research centre told AFP Tuesday, with marine heatwaves in some places exceeding 30 degrees Celsius.

On August 11, the daily median surface temperature of the Mediterranean reached 28.67C, said Justino Martinez, researcher at the Institut de Ciencies del Mar in Barcelona and the Catalan Institute of Research for the Governance of the Sea.

This comes close to July 24, 2023, when the Mediterranean Sea broke its daily heat record with a median temperature of 28.71C.

The preliminary readings for 2024 come from satellite data from the European Copernicus Observatory.

The Mediterranean basin is one of the hot spots of global warming.

For the second consecutive year, its the waters are warmer than the previous record set on August 23, 2003 when the daily median temperature reached 28.25C amid an exceptional heatwave.

"What is remarkable is not so much to reach a maximum on a given day, but to observe a long period of high temperatures, even without breaking a record," said Martinez.

"Since 2022, surface temperatures have been abnormally high for long periods, even in a climate-change environment," he said.

This year, the 2023 level was reached "more than 15 days later and usually the sea surface temperature in the Mediterranean is expected to decrease from the end of August", he added.

Locally, waters above very unusual 30C were recorded (4C above normal) along the coasts of Spain, France and Italy.

Oceans have absorbed 90 percent of the excess heat produced by human activity since the dawn of the industrial age, according to scientists.

This excess heat continues to accumulate as greenhouse gases, mainly from burning oil, gas and coal.

The overheating of the oceans is predicted to impact marine plant and animal life, including on the migration of certain species and the spread of invasive species.

This could threaten fish stocks and thus undermine food security in certain parts of the globe.

Warmer oceans are also less capable of absorbing carbon dioxide (CO2), reinforcing the vicious cycle of global warming.