Scientists warn of disastrous effects of warming Mediterranean


MADRID– While holidaymakers could enjoy the summer heat of the Mediterranean Sea, climatologists are warning of dire consequences for its marine life as it burns in a series of severe heat waves.

From Barcelona to Tel Aviv, scientists say they are witnessing exceptional temperature rises ranging from 3 degrees Celsius (5.4 Fahrenheit) to 5 degrees Celsius (9 Fahrenheit) above the norm for this time of year. Water temperatures regularly exceeded 30 C (86 F) on some days.

Extreme heat in Europe and other countries around the Mediterranean has been in the headlines this summer, but rising sea temperatures are largely out of sight and far from mind.

Marine heat waves are caused by ocean currents that create areas of warm water. Weather systems and heat in the atmosphere can also increase the water temperature in degrees. And just like their terrestrial counterparts, marine heat waves are longer, more frequent and more intense due to human-induced climate change.

The situation is “very worrying”, says Joaquim Garrabou, researcher at the Barcelona Institute of Marine Sciences. “We are pushing the system too far. We must act on climate issues as soon as possible.

Garrabou is part of a team that recently published the report on heatwaves in the Mediterranean Sea between 2015 and 2019. The report says these phenomena have led to “massive mortality” of marine species.

About 50 species, including corals, sponges and algae, have been affected along thousands of kilometers of Mediterranean coastline, according to the study published in the journal Global Change Biology.

The situation in the eastern basin of the Mediterranean is particularly dire.

The waters off Israel, Cyprus, Lebanon and Syria are “the hottest hotspot in the Mediterranean, for sure,” said Gil Rilov, a marine biologist at the Israel Institute for Oceanographic Research. and limnology and one of the co-authors of the article. Average summer sea temperatures are now regularly above 31°C (88°F).

These warming seas are pushing many native species to the brink, “because every summer their optimum temperature is exceeded,” he said.

What he and his colleagues are witnessing in terms of biodiversity loss is what is expected to happen further west in the Mediterranean towards Greece, Italy and Spain in the coming years.

Garrabou points out that the seas have served the planet by absorbing 90% of the Earth’s excess heat and 30% of the carbon dioxide emitted into the atmosphere by the production of coal, oil and gas. This carbon sink effect protects the planet from even harsher climatic effects.

This was possible because the oceans and seas were in good condition, Garrabou said.

“But now we’ve driven the ocean into an unhealthy, dysfunctional state,” he said.

While the planet’s greenhouse gas emissions will need to be drastically reduced if sea warming is to be limited, ocean scientists are specifically looking for authorities to ensure that 30% of marine areas are protected from human activities such as fishing, which would give the species a chance to recover and thrive.

About 8% of the Mediterranean Sea area is currently protected.

Garrabou and Rilov said policymakers are largely ignoring Mediterranean warming and its impact.

“It’s our job as scientists to bring this to their attention so they can think about it,” Rilov said.

Heat waves occur when particularly hot weather continues for a number of days, with no rain or little wind. Terrestrial heatwaves help cause marine heatwaves and the two tend to feed into a vicious circle of warming.

Onshore heatwaves have become commonplace in many countries around the Mediterranean, with dramatic side effects like wildfires, droughts, crop failures and excruciatingly high temperatures.

But marine heatwaves could also have serious consequences for countries bordering the Mediterranean and the more than 500 million people who live there if not addressed quickly, scientists say. Fish stocks will be depleted and tourism will be affected as destructive storms could become more frequent on land.

Although it represents less than 1% of the world’s ocean surface, the Mediterranean is one of the main reservoirs of marine biodiversity, containing between 4% and 18% of the world’s known marine species.

Some of the most affected species are essential to maintaining the functioning and diversity of marine habitats. Species like Posidonia oceanica seagrass beds, which can absorb large amounts of carbon dioxide and are home to marine life, or coral reefs, which are also home to wildlife, would be at risk.

Garrabou says mortality impacts on species have been observed between the surface and 45 meters (about 150 feet) deep, where recorded marine heat waves were exceptional. Heat waves affected more than 90% of the surface of the Mediterranean Sea.

According to the most recent scientific papers, the sea surface temperature in the Mediterranean has increased by 0.4 C (0.72 F) every decade between 1982 and 2018. On an annual basis, it has increased by around 0. 05 C (0.09 F) over the past decade with no signs of letting up.

Even fractions of a degree can have disastrous effects on ocean health, experts say.

The affected areas have also grown since the 1980s and now cover most of the Mediterranean, the study suggests.

“The question is not about the survival of nature, because biodiversity will find a way to survive on the planet,” Garrabou said. “The question is, if we continue in this direction, maybe our society, the humans, won’t have a place to live.”


Ilan Ben Zion reported from Jerusalem.


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