Extract from ABC News
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 heatwaves.
Key points:
- Scientists say they are witnessing exceptional temperature hikes in the Mediterranean Sea, ranging from 3C to 5C above the norm
- Warming of even a fraction of a degree can have disastrous effects on ocean health
- Land heatwaves help cause marine heatwaves, and the two tend to feed each other in a vicious, warming cycle
From Barcelona to Tel Aviv, scientists say they are witnessing exceptional temperature hikes, ranging from 3 to 5 degrees Celsius above the norm for this time of year.
Water temperatures have regularly exceeded 30C on some days.
Extreme heat in Europe and other countries around the Mediterranean Sea has grabbed headlines this summer, but the rising sea temperature is largely out of sight and out of mind.
Marine heatwaves 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.
And, just like their on-land counterparts, marine heatwaves 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.
"The question is not about the survival of nature, because biodiversity will find a way to survive on the planet," he says. "The question is if we keep going in this direction maybe our society, humans, will not have a place to live.
"We are pushing the system too far. We have to take action on the climate issues as soon as possible."
Seas no longer effective carbon sinks
Dr Garrabou is part of a team that recently published a report on heatwaves in the Mediterranean Sea between 2015 and 2019, which 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.
The situation in the eastern Mediterranean basin is particularly dire.
The waters off Israel, Cyprus, Lebanon and Syria are "the hottest hot spot in the Mediterranean, for sure", says Gil Rilov, a marine biologist at Israel's Oceanographic and Limnological Research institute, and one of the paper's co-authors.
Average sea temperatures in the summer are now consistently in excess of 31C, driving many native species to the brink "because every summer their optimum temperature is being exceeded", Dr Rilov says.
What he and his colleagues are witnessing in terms of biodiversity loss is what is projected to happen further west in the Mediterranean Sea towards Greece, Italy and Spain in the coming years.
Dr Garrabou points out that seas have been serving the planet by absorbing 90 per cent of the Earth's excess heat and 30 per cent of its carbon dioxide emitted into the atmosphere by coal, oil and gas production.
This carbon-sink effect shields the planet from even harsher climate effects.
However, that's only been possible because the oceans and seas were previously in a healthy condition, Dr Garrabou says.
"Now we have driven the ocean to an unhealthy and dysfunctional state," he says.
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 per cent of sea areas are protected from human activities such as fishing, which would give species a chance to recover and thrive.
About 8 per cent of the Mediterranean Sea area is currently protected.
Dr Garrabou and Dr Rilov say policymakers are largely unaware of the warming Mediterranean and its impact.
"It's our job, as scientists, to bring this to their attention so they can think about it," Dr Rilov says.
Marine heatwaves affect fish stocks, biodiversity, tourism
Heatwaves occur when especially hot weather continues over a set number of days, with no rain or little wind.
Land heatwaves help cause marine heatwaves, and the two tend to feed each other in a vicious, warming cycle.
Land heatwaves have become commonplace in many countries around the Mediterranean, with dramatic side effects such as wildfires, droughts, crop losses and excruciatingly high temperatures.
However, scientists say, marine heatwaves could also have serious consequences for countries bordering the Mediterranean Sea and the more than 500 million people who live there if their causes are not dealt with soon.
Fish stocks will be depleted and tourism will be adversely affected, as destructive storms could become more common on land.
Despite representing less than 1 per cent of the global ocean surface area, the Mediterranean Sea is one of the main reservoirs of marine biodiversity, containing between 4 per cent and 18 per cent of the world's known marine species.
Some of the most-affected species are key to maintaining the functioning and diversity of the sea's habitats.
Species such as the Posidonia oceanica seagrass meadows, which can absorb vast amounts of carbon dioxide and shelter marine life, or coral reefs, which are also home to wildlife, would be at risk.
Dr Garrabou says the mortality impacts on species were observed between the surface and 45 metres deep, where the recorded marine heatwaves were exceptional.
Heatwaves affected more than 90 per cent of the Mediterranean Sea's surface.
According to the most-recent scientific papers, the sea surface temperature in the Mediterranean has increased by 0.4C each decade between 1982 and 2018. It has been rising by some 0.05C on a yearly basis over the past decade, without any sign of letting up.
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 Sea, the study suggests.
AP
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