Extreme heat in Europe and other countries around the Mediterranean has grabbed headlines this summer, but the rising sea temperature is largely out of sight and out of mind.
While vacationers might enjoy the Mediterranean Sea's summer warmth, climate scientists are warning of dire consequences for its marine life as it burns up in a series of severe heat waves.
From Barcelona to Tel Aviv, scientists say they are witnessing exceptional temperature hikes ranging from 3 degrees Celsius to 5 degrees Celsius above the norm for this time of year. Water temperatures have regularly exceeded 30 C on some days.
Marine heat waves are caused by ocean currents building up areas of warm water. Weather systems and heat in the atmosphere can also pile on degrees to the water's temperature.
Just like their counterparts on ground, marine heat waves are longer, more frequent and more intense because of human-induced climate change.
Despite representing less than 1 percent of the global ocean surface area, the Mediterranean is one of the main reservoirs of marine biodiversity, containing between 4 percent and 18 percent of the world’s known marine species.
The situation is “very worrying,” says Joaquim Garrabou, a researcher at the Institute of Marine Sciences in Barcelona. “We are pushing the system too far. We have to take action on the climate issues as soon as possible.”
Garrabou is part of a team that recently published a report on heat waves 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 seaweed, were affected along thousands of kilometres of Mediterranean coasts, according to the study, which was published in the Global Change Biology journal.
Oceans, seas in 'dysfunctional' states
Garrabou points out that seas have been serving the planet by absorbing 90 percent of the earth’s excess heat and 30 percent of carbon dioxide emitted into the atmosphere by coal, oil and gas production.
This carbon-sink effect shields the planet from even harsher climate effects. But humans have driven the ocean to "an unhealthy and dysfunctional state," he said.
While the earth's greenhouse gas emissions will have to be drastically reduced if sea warming is to be curtailed, ocean scientists are specifically looking for authorities to guarantee that 30 percent of sea areas are protected from human activities such as fishing, which would give species a chance to recover and thrive.
About 8 percent of the Mediterranean Sea area is currently protected.
Consequences on land
Marine heat waves could have serious consequences for the countries bordering the Mediterranean if it's not dealt with soon, scientists say.
Some of the most affected species are key to maintaining the functioning and diversity of the sea's habitats.
Species like the Posidonia Oceanica seagrass meadows, which can absorb vast amounts of carbon dioxide and shelters marine life, or coral reefs, which are also home to wildlife, would be at risk.