By the year 2300, life in the oceans will face a possible mass mortality comparable to the great extinctions of the Earth if humanity cannot reduce greenhouse gas emissions, warns a study published in the journal Science on Thursday (28).

But limiting global warming to 2°C above pre-industrial levels will prevent such a catastrophe, said the paper's authors, Justin Penn and Curtis Deutsch, both of which are linked to the University of Washington and Princeton University.

Scientists used ecophysiological models to weigh the physical limits of the species in relation to projected sea temperatures and depletion of oxygen levels, a particularly challenging task due to the lack of previous research on the subject.

The results were alarming: if global warming continues as it is, marine ecosystems around the planet could suffer mass extinction comparable to the end of the Permian, known as the "Great Death."

This happened 250 million years ago and led to the disappearance of more than two-thirds of marine fauna due to warming and oxygen depletion, conditions similar to those of today.

While tropical oceans would lose most species, many would migrate to higher latitudes to survive. On the other hand, polar species would disappear en masse, as their habitat types would disappear completely from the planet.

Limiting warming to 2°C, the upper limit of the target set by the Paris Agreement, "would reduce the severity of extinctions by more than 70%, avoiding a marine mass extinction," the document says.

The established target of limiting warming to 1.5°C is impossible to achieve with current international commitments, according to UN climate experts.

"Because marine extinctions have not progressed as far as land extinctions, society has time to turn the tide in favor of marine life," scientists Malin Pinsky and Alexa Fredston wrote in a commentary.

"Exactly where the future lies between the best and worst-case scenario will be determined by the choices society makes not only about climate change, but also about habitat destruction, overfishing and coastal pollution," they said.

Source: GZH Ambiente