Without a reduction in greenhouse gas emissions, ocean species could be decimated by 2300, comparable to a mass extinction event about 250 million years ago, warns a study published Thursday in the prestigious journal Science.
But limiting global warming to 2°C compared to the pre-industrial era would avoid this catastrophic scenario, the researchers point out.
The latter used models that analyzed the relationship between global warming, the resulting decline in oxygen levels in water, and the levels of O2 necessary for species survival.
Particularly complicated to study, such projections of extinction risks in the oceans have so far been formulated very little.
But the results are alarming: If emissions of planet-warming greenhouse gases continue to accelerate, the oceans could experience a Permian-like mass extinction by the year 2300.
During this catastrophic event, marine biodiversity was reduced to its absolute minimum under the combined effects of rising temperatures and falling oxygen levels in the oceans, a trajectory that continues today.
In this scenario, the tropical oceans would lose most species, but many species from those areas would migrate to other regions to survive.
On the other hand, the polar species would disappear en masse because they would no longer have a place to go.
Source of hope, a scenario that limits warming to 2°C would allow it to “reduce the severity of species extinctions by 70% and avoid mass extinctions,” according to the study.
Out of range target
The Paris Agreement, the international reference text, aims to limit global warming to “well below 2°C compared to pre-industrial levels” and if possible to +1.5°C.
According to UN climate experts (IPCC), this goal is “out of reach” with current international commitments.
“Because marine extinctions are not as advanced as they are on land, our society has time to turn the tide in favor of ocean life,” scientists wrote in an article accompanying the study.
“Exactly where our future lies between the best and worst scenarios will be determined by the societal choices made,” they added.