Extreme global warming could see major ocean life extinction

A computer model based on past mass extinctions predicts the percentages of marine organisms that may be lost in best and worst-case scenarios

By Michael Le Page

How badly will ocean animals be hit as Earth warms? A computer model based on the oxygen requirements of marine organisms may provide an answer.

Our oceans already contain about 2 per cent less oxygen than 50 years ago, because the gas is less soluble in warmer water. Many organisms are therefore moving polewards to cooler regions. As the oceans continue to warm, some will be left with nowhere to go, with polar species being hit hardest.

To better understand the scale of the risk, Curtis Deutsch at Princeton University and Justin Penn at the University of Washington in Seattle have developed a model that predicts when animal species may go extinct. This is based on projections of when the amount of suitable habitat available to marine species will fall below a critical level, due to oxygen declines.

They calibrated their model using data from past mass extinctions. The model doesn’t take into account other pressures on marine life, such as overfishing, pollution and the loss of coral reefs from bleaching.

Nevertheless, the model suggests marine extinctions will rise gradually alongside ocean warming, passing 10 per cent once around 6°C of warming on average across the seas is reached. After 8°C, the percentage will increase more rapidly, passing 40 per cent at around 14°C of warming.

One key uncertainty is how quickly marine organisms will colonise new habitats. If they move more quickly than in the median scenario, the proportion of species going extinct would remain well below 5 per cent until around 8°C of warming.

The paper cites the 2021 report by the Intergovernmental Panel on Climate Change (IPCC) to show temperature increases of this magnitude are possible.

“Under the high-emissions scenario, surface air warming could reach… 10° to 18°C over the next three centuries,” the paper states. However, this high-emissions scenario isn’t considered likely and the world is thought to be heading for around 3°C by 2100.

“We aren’t predicting the future or taking anything as a given,” says Deutsch. “We are saying that still plausible projections of the future will result in a mass extinction. Scenarios that mitigate strongly will avoid that outcome.”

Writing in an editorial that accompanies the research, Malin Pinsky at Rutgers University in New Jersey said: “Fortunately, greenhouse gas emissions are not on track for the worst-case scenario.

“How close to the best-case scenario human society can hew, however, remains one of the most pressing questions for the future of life in the oceans.”

Journal reference: Science, DOI: 10.1126/science.abe9039