Climate change could cause mass marine extinction, study finds

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Not since an asteroid wiped out the dinosaurs – along with half of all other beings on Earth – has life in the ocean been so threatened.

Warm waters cook creatures in their own habitats. Many species are slowly suffocating as oxygen escapes from the seas. Even populations that have managed to withstand the ravages of overfishing, pollution and habitat loss are struggling to survive in the face of accelerating climate change.

If humanity’s greenhouse gas emissions continue to rise, according to a new study published Thursday, around a third of all marine animals could disappear within 300 years.

The results, published in the journal Science, reveal a potential mass extinction looming beneath the waves. The oceans have absorbed a third of the carbon and 90% of the excess heat created by humans, but their vast expanse and impressive depths mean scientists are only just beginning to understand what the creatures are up against.

Yet the study by Princeton University Earth scientists Justin Penn and Curtis Deutsch also highlights how much more marine life could still be saved. If the world takes swift action to reduce fossil fuel use and restore degraded ecosystems, researchers say, it could reduce potential extinctions by 70%.

“This is a landmark paper,” Malin Pinsky, a Rutgers University biologist who did not contribute to the paper, said in an interview. “If we’re not careful, we’re heading into a future that I think for all of us right now would seem pretty hellish. … This is a very important warning signal.

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The world has already warmed by more than 1 degree Celsius (1.8 degrees Fahrenheit) since pre-industrial times, and last year the oceans contained more thermal energy than at any time since records began six decades ago.

These rising ocean temperatures are shifting the boundaries of comfort zones for sea creatures. Many are fleeing north in search of cooler waters, causing the “disappearance” – or local disappearance – of once-common species.

Polar creatures that can only survive in the most icy conditions may soon find themselves with nowhere to go. Species that cannot move easily in search of new habitats, such as fish that depend on specific coastal wetlands or geological formations on the sea floor, will be more likely to disappear.

Using climate models that predict species behavior based on simulated organism types, Deutsch and Penn found that the number of extinctions, or local extinctions of particular species, increases by about 10% with each degree Celsius warming.

The researchers tested their models by using them to simulate a mass extinction at the end of the Permian period, when catastrophic warming triggered by volcanic eruptions wiped out around 90% of all life on Earth. Because the models successfully replicated events 250 million years ago, scientists were confident in their predictions of what might happen 300 years from now.

Penn and Deutsch’s research found that most animals cannot afford to lose more than 50% of their habitat – beyond that number, the species slides into irreversible decline. In worst-case emissions scenarios, losses would be equivalent to the five worst mass extinctions in Earth’s history.

These changes are already starting to happen. In the 1980s, a heat wave in the Pacific wiped out a small, silvery fish called the Galapagos damselfish from the waters off Central and South America. A hotspot along the Uruguayan coast has led to mass shellfish kills and widespread changes in fishermen’s catches. Japan’s salmon fisheries have plummeted as sea ice recedes and warmer, nutrient-depleted waters invade the region.

The danger of warming is compounded by the fact that warmer waters begin to lose dissolved oxygen – even though higher temperatures speed up the metabolism of many marine organisms, so they need more oxygen to live.

The ocean contains only one sixtieth more oxygen than the atmosphere; even less so in warmer regions where water molecules are less able to keep precious oxygen from bubbling up in the air. As global temperatures rise, this reservoir shrinks even further.

Warming sea surfaces also cause the ocean to stratify into distinct layers, making it harder for the warmer, oxygenated waters above to mix with the colder depths. Scientists have documented the expansion of “shadow zones” where oxygen levels are so low that most life cannot survive.

Deoxygenation poses one of the biggest climate threats to marine life, said Deutsch, one of the study co-authors. Most species can expend a little extra energy to cope with higher temperatures or adapt to increased acidity. Even some corals have found ways to keep their calcium carbonate skeleton from eroding in more acidic waters.

“But there is no price organisms can pay to get more oxygen,” Deutsch said. “They’re just sort of stuck.”

Humanity’s greatest ally against climate change is the Earth itself

This climate-driven marine mortality is just one element of a broader biodiversity crisis affecting the entire world. A recent report by the Intergovernmental Panel on Climate Change revealed that global warming has already contributed to the disappearance of at least 400 species. A separate UN panel has found that around 1 million more species are at risk of extinction due to overexploitation, habitat destruction, pollution and other human disturbances of the natural world.

A comprehensive new assessment published Wednesday in the journal Nature showed that more than 20% of reptile species could disappear. Turtles and crocodiles are the most endangered, with more than half of each group at least vulnerable to extinction in the near future.

The consequences for communities that depend on reptiles for food, pest control, culture and other services could be profound.

“If we start messing up ecosystems and the services they provide, that has repercussions,” said co-author Neil Cox, head of the biodiversity assessment unit at the International Union for Conservation. of nature. “I think the threats to biodiversity are as serious as climate change, we just underestimate them.”

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Yet the two crises are closely linked, added Blair Hedges, an evolutionary biologist at Temple University and a contributor to Reptile Assessment. Climate change can accelerate the disappearance of populations already destabilized by habitat degradation or hunting. Ecosystems that lose key species may be less able to extract carbon from the atmosphere or protect against climate impacts.

Researchers have pinpointed the fate of the lesser Virgin Gorda gecko, a thumbnail-sized reptile that lives in moist pockets of soil on Caribbean hillsides. The creation of national parks on the islands where the gecko is found has prevented the loss of habitat that could have doomed the species. But now her home is drying up due to climate change, once again raising the specter of extinction.

“If you have multiple threats…working together, often even when you think one of them is under control, the other turns out to be even more of a threat,” Hedges said.

While the danger to the animals — and the humans who depend on them — is undeniably grave, Pinsky, the Rutgers biologist, urged not to give in to despair.

In an analysis for Science that accompanied Penn and Deutsch’s report, he and Rutgers ecologist Alexa Fredston compared marine animals to canaries in a coal mine, alerting humanity to unseen forces – such as the dangerous buildup of carbon dioxide and oxygen loss in the oceans – which also threaten our capacity. to survive. If people can take action to save marine wildlife, we will eventually save ourselves.

“It’s scary, but it’s also empowering,” Pinsky told the Post.

“What we do today and tomorrow and the rest of this year and next year will have really big consequences,” he added. “It’s not ‘once in a lifetime’ but maybe ‘once in a lifetime’.”

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Teresa H. Sadler