Without greenhouse gas reductions, mass extinction in the oceans is possible

A source of hope, limiting global warming to 2°C compared to the pre-industrial era would make it possible to avoid this catastrophic scenario.

If greenhouse gas emissions are not reduced, species living in the oceans could be decimated by 2300, warns a study published Thursday, April 28 in the journal Science. But limiting global warming to 2°C compared to the pre-industrial era would avoid this worst-case scenario, the researchers point out.

The latter used models analyzing the link between global warming, the resulting drop in the quantities of oxygen in the water, and the quantities of dioxygen (O2) necessary for the survival of species. Particularly complicated to study, such projections of the risks of extinction in the oceans had until now been very little formulated.

But the results are alarming: if emissions of greenhouse gases warming the planet continue to increase, then the oceans could experience a mass extinction comparable to that of the Permian. During this catastrophic event, marine biodiversity was reduced to its bare minimum, under the combined effect of rising temperatures and declining oxygen in the oceans, a scenario also unfolding today.

A source of hope

Under this scenario, the tropical oceans would lose the most species, but many species from these areas would migrate to other regions to survive. The polar species would disappear massively, having no place to take refuge.

A source of hope, a scenario limiting warming to 2°C would “reduce the severity of extinctions by 70%, avoiding a mass extinction”, according to the study.

The Paris Agreement, an international reference text, sets the objective of containing global warming “well below 2°C compared to pre-industrial levels”, and if possible at + 1.5°C. That goal is “out of reach” with current international commitments, according to the UN’s Intergovernmental Panel on Climate Change.

“Because marine extinctions have not progressed as far as those on land, our society has time to turn the tide in favor of life in the oceans,” scientists wrote in a commentary article accompanying the study, however. . “Where exactly our future lies between the best and worst case scenario will be determined by the societal choices made,” they added.