MADRID (AP) – While tourists can enjoy the summer heat of the Mediterranean Sea, climate scientists are warning of dire consequences for 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 made headlines this summer, but rising sea temperatures are largely out of sight and out of mind.
Marine heat waves are caused by ocean currents that build up areas of warm water. Weather systems and heat in the atmosphere can also accumulate in degrees at the temperature of water. And, like their terrestrial counterparts, marine heat waves are longer, more frequent and more intense because of human-induced climate change.
The situation is “very worrying”, says Joaquim Garrabou, a researcher at the Institute of Marine Sciences in Barcelona. “We are taking the system too far. We have to act on climate issues as quickly as possible.”
Garrabou is part of a team that recently published the 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 kilometers of Mediterranean coasts, according to the study, published in the journal Global Change Biology.
The situation in the eastern Mediterranean basin 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 and Limnological Research and one of the paper’s co-authors. Average summer sea temperatures are now consistently above 31 C (88 F).
These warm seas are pushing many native species to the edge of the cliff, “because every summer their ideal temperature is exceeded,” he said.
What he and his colleagues are witnessing in terms of biodiversity loss is what is predicted to happen further west of 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 more severe weather effects.
This was possible because the oceans and seas were in healthy condition, Garrabou said.
“But now we’ve taken the ocean to an unhealthy and dysfunctional state,” he said.
While Earth’s greenhouse gas emissions will have to be drastically reduced if sea warming is to be reduced, ocean scientists are specifically looking to authorities to ensure that 30% of maritime areas are protected from human activities such as fishing, that 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 were largely unaware of Mediterranean warming and its impact.
“It’s our job as scientists to bring attention to this so they can think about it,” Rilov said.
Heat waves occur when especially hot weather continues for a certain number of days, with no rain or little wind. Terrestrial heatwaves help to cause marine heatwaves and the two tend to feed off each other in a vicious cycle of warming.
Terrestrial heatwaves have become commonplace in many countries around the Mediterranean, with dramatic side effects such as forest fires, droughts, crop failures and extremely high temperatures.
But marine heat waves can also have serious consequences for countries bordering the Mediterranean and the more than 500 million people who live there if not treated soon, scientists say. Fish stocks will be depleted and tourism will be negatively affected as destructive storms may become more common on land.
Despite representing less than 1% of the global 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 critical to maintaining the functioning and diversity of marine habitats. Species such as Posidonia oceanica seagrass meadows, which can absorb large amounts of carbon dioxide and harbor marine life, or coral reefs, which also harbor wildlife, would be at risk.
Garrabou says the impacts of mortality on the species were 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 articles, the sea surface temperature in the Mediterranean has increased by 0.4 C (0.72 F) every decade between 1982 and 2018. Annually, it has increased by about 0.05 C (0.09 F) over the last decade without any sign of slowing down.
Even fractions of degrees 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 issue is not about the survival of nature, because biodiversity will find a way to survive on the planet,” said Garrabou. “The thing is, if we continue in this direction, maybe our society, humans, don’t have a place to live.”
Ilan Ben Zion reported from Jerusalem.
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