The uncontrolled greenhouse gas emissions that are raising global temperatures are also warming the oceans. And as the water temperature rises, the availability of oxygen decreases, which threatens to cause a mass extinction of marine biodiversity in the coming centuries. This is the conclusion of at least one study conducted by researchers at the universities of Washington and Princeton (United States), and published in the magazine Science.
According to the authors of this work, if emissions are not reduced and continued at the current rate, this marked reduction in marine life abundance will would be similar to what happened 250 million years agothe so-called Permian-Triassic mass extinction, also called the Great Dying, when more than two-thirds of marine life has disappeared. Thus, tropical waters would experience the greatest loss of biodiversity, while polar species would be the most likely to disappear.
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The extinction of the sea: the result of warmer water
Professors Justin L. Penn and Curtis Deutsch, authors of the study, combined existing physiological data on marine species with patterns of climate change to predict how changes in habitat conditions will affect marine animal survival, as reported by Princeton University.
They then compared their model projection of future marine biodiversity to past mass extinctions, known primarily from the fossil record. And they found that their model, the Permian-Triassic extinction, and the distribution of species we see now follow similar dynamics: Climate warming is linked to the loss of oxygen from the oceans, and this phenomenon ultimately leads to a drastic reduction of marine life.
This is because warm water contains less oxygen than cold water, causing slower ocean circulation that reduces the supply of this vital element at depth. Paradoxically, the metabolic rates of the species increase with water temperature, so oxygen demand increases as supply decreases. “Once the available oxygen is less than what the species needs, we expect significant losses,” Penn explained. To this we should add that warmer water itself is a risk factor for living things adapted to colder climates.
Also other research by Penn and Deutsch, also published in Science in 2018, showed that an increase in metabolic oxygen demand coupled with temperature, along with reduced oxygen availability caused by volcanic eruptions, could explain the geographic patterns of mass loss of species during the Permian-Triassic extinction event.
Limited adaptability
Marine animals have physiological mechanisms that allow them to cope with environmental changes, but only to a certain extent, the study repeated by Princeton University points out. In that sense, the authors indicate that polar species are more likely to become extinct because they wouldn’t have a suitable habitat to move to.
in contrast, tropical marine species would fare better because they have characteristics that allow them to adapt to warm water with little oxygen. However, the equatorial ocean is already so hot and so low in oxygen that a further increase in temperature – resulting in a decrease in this chemical element – could make it uninhabitable for many species.
Still in time to avoid a mass extinction of the sea
Despite everything, Professors Penn and Deutsch believe we still have time to turn the situation around and highlight possible solutions. “The future isn’t set in stone,” says Penn, en cutting greenhouse gas emissions could “reduce extinction risk by more than 70%”according to the research, helping to preserve the marine biodiversity built up during the last 50 million years of evolutionary history.
That is why both experts are urging action. “Rapid and aggressive reductions in greenhouse gas emissions are essential,” says Deutsch. In the same sentence, Penn manifests: “There is still plenty of time to change the trajectory of carbon dioxide emissions and avoid the size of the warming that would cause this mass extinction.”
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