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Since the asteroid destroyed the dinosaurs – along with half of all other creatures on Earth – life in the ocean has not been so endangered.
Warm waters are cooked creatures in their own habitats. Many species suffocate slowly as oxygen leaks from the seas. Even populations that have withstood the ravages of overfishing, pollution and habitat loss are struggling to survive amid accelerating climate change.
If humanity’s greenhouse gas emissions continue to rise, according to a new study published Thursday, about a third of all marine animals could disappear within 300 years.
The findings, 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 percent of the excess heat created by humans, but their vast expanses and forbidden depths mean that scientists are just beginning to understand what the creatures there are facing.
However, a study by Earth scientists at Princeton University Justin Penn and Curtis Deutsch also highlights how much marine life can still be saved. If the world takes swift action to limit fossil fuel use and restore degraded ecosystems, researchers say, it could reduce potential extinction by 70 percent.
“This is a remarkable article,” said Malin Pinsky, a biologist at Rutgers University who did not contribute to the article. “If we are not careful, we are moving towards a future that I think would look pretty hellish for all of us right now. … This is a very important wake-up call. ”
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The world has already warmed by more than 1 degree Celsius (1.8 degrees Fahrenheit) from the pre-industrial era, and last year the oceans contained more heat than at any time since record-keeping began six decades ago.
These rising ocean temperatures are pushing the boundaries of sea creatures’ comfort zones. Many are fleeing north in search of cooler waters, leading to the “destruction” – or local extinction – of once-common species.
Polar creatures, which can only survive in the coldest conditions, may soon find themselves without a place to go. Species that cannot move easily in search of new habitats, such as fish that depend on specific coastal wetlands or seabed geological formations, are more likely to become extinct.
Using climate models that predict species behavior based on simulated species, Deutsche and Penn found that the number of extirpations or local extinctions of certain species increased by about 10 percent with every 1 degree Celsius warming.
The researchers tested their models, using them to simulate a mass extinction at the end of the Permian period, when catastrophic warming caused by volcanic eruptions destroyed approximately 90 percent of all life on Earth. As the models successfully reproduce events 250 million years ago, scientists were confident in their predictions of what might happen 300 years from now.
Research by Penn and Deutsch has found that most animals cannot afford to lose much more than 50 percent of their habitat – beyond that, the species is heading for irreversible decline. In the worst case scenario, the losses would be equal to the five worst mass extinctions in Earth’s history.
These changes are already beginning to develop. In the 1980s, a heat wave in the Pacific Ocean eliminated a small silverfish called a Galapagos girl from the waters of Central and South America. A hotspot off the coast of Uruguay has led to the mass extinction of shellfish and widespread changes in fishermen’s catches. Japan’s salmon fishing has declined as sea ice recedes and warmer, more nutrient-depleted waters invade the region.
The danger of warming is compounded by the fact that hotter waters are beginning to lose dissolved oxygen – although higher temperatures speed up the metabolism of many marine organisms, so they need more oxygen to live.
The ocean contains only one-sixth of the oxygen in the atmosphere; even less so in warmer regions, where water molecules are less able to retain valuable oxygen from bubbling back into the air. As global temperatures rise, this reservoir shrinks even more.
The warming of the sea surface also causes the ocean to stratify into separate layers, making it difficult to mix warmer, oxygen-enriched waters from above with cooler depths. Scientists have documented the expansion of “shadow zones” where oxygen levels are so low that most lives cannot survive.
Deoxygenation is one of the biggest climate threats to marine life, said Deutsch, one of the co-authors of the study. Most species can expend a little extra energy to cope with higher temperatures or to adapt to increasing acidity. Even some corals have found ways to protect their calcium carbonate skeletons from erosion in more acidic waters.
“But there is no price that organisms can pay to get more oxygen,” Deutsch said. “They’re just stuck.”
Mankind’s greatest ally against climate change is the Earth itself
This climate-induced marine death is just part of a wider global biodiversity crisis. A recent report by the Intergovernmental Panel on Climate Change found that warming has already contributed to the extinction of at least 400 species. A separate UN panel has found that about 1 million additional species are threatened with extinction as a result of overexploitation, habitat destruction, pollution and other human disturbances.
A comprehensive new estimate, published Wednesday in the journal Nature, found that more than 20 percent of reptiles may 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 rely on reptiles for food, pest control, culture and other services can be profound.
“If we start confusing the ecosystems and the services they provide, it has negative effects,” said co-author Neil Cox, manager of the International Union for Conservation of Nature’s biodiversity assessment department. “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 intertwined, added Blair Hedges, an evolutionary biologist at Temple University and a participant in the reptile assessment. Climate change can accelerate the death of populations that are already destabilized by habitat degradation or hunting. Ecosystems that lose key species may be less able to remove carbon from the atmosphere or buffer against climate impacts.
Researchers have highlighted the plight of the Virgin Gorda gecko, a miniature reptile that lives in moist pockets of soil in the Caribbean hills. The creation of national parks on gecko islands has helped prevent habitat loss that could doom the species. But now his home is drying up from climate change, raising the specter of extinction again.
“If you have multiple threats … to work together, often even when you think one of them is under control, then the other is an even bigger threat,” Hedges said.
Although the danger to animals – and the people who depend on them – is undeniably terrible, Pinsky, the Rutgers biologist, urged you not to despair.
In an analysis for Science that accompanies the Penn and Deutsch report, he and Rutgers ecologist Alexa Fredston likened marine animals to canaries in a coal mine, warning humanity of invisible forces – such as dangerous carbon dioxide and ocean oxygen loss – which also threaten our ability to survive. If people can take action to preserve wildlife in the ocean, we will save ourselves.
“It’s scary, but it also gives an opportunity,” Pinsk told The Post.
“What we are doing today and tomorrow, and the rest of this year and next, have really important consequences,” he added. “This is not ‘once in a lifetime’, but perhaps ‘once in a lifetime’.
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