Climate crisis threatens to wipe out almost all sea life, scientists warn
- A paper published in the journal ‘Science’ found that accelerating greenhouse gas emissions could culminate in a mass extinction not seen for 250 million years
- Limiting the temperature rise to 2 degrees Celsius would reduce the risk of mass extinction by more than 70 per cent, the scientists said
Accelerating greenhouse gas emissions could “culminate in a mass extinction rivalling those in Earth’s past”, stated a peer-reviewed paper published on Thursday in the journal Science.
There is still time, though, to forestall such a global catastrophe, the scientists said. Limiting the temperature rise to 2 degrees Celsius would reduce the risk of mass extinction by more than 70 per cent, according to the paper.
“The future isn’t yet written,” said Justin Penn, an associate research scholar at Princeton University and lead author of the study. “It’s not too late to reverse the greenhouse gas emissions trends to avoid mass extinction in the ocean from climate change.”
If the future remains a blank page, the past consequences of extreme climate change are written in the marine fossil record. In a 2018 study, Penn and co-author Curtis Deutsch created a computer model to simulate the warming of the world in the late Permian Period 250 million years ago when volcanic eruptions released huge quantities of greenhouse gases into the atmosphere.
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They found ocean surface temperatures increased by more than 10 degrees, triggering a nearly 80 per cent decline in marine oxygen levels. An examination of the fossil record confirmed that oxygen-depleted warming seas killed off up to 96 per cent of marine species.
Today, ocean temperatures are rising to record highs and oxygen levels are falling. “The same mechanism that would be driving species losses from human-induced climate change has been shown to have caused extinction in the geologic past,” Penn said.
He and Deutsch, a professor of geosciences at Princeton, built on that research for their new paper. To estimate extinction probabilities, they created a model that simulated future climate change and incorporated current assessments of marine animals’ vulnerability to human-related threats such as pollution and overfishing. The researchers then calculated the levels of oxygen depletion that would render the ocean uninhabitable for various species.
The scientist found that if global temperatures increase around 4.9 degrees by the end of the century and continue to rise, it would trigger a mass extinction on par with the end of the Permian Period.
Under a low-emissions scenario that keeps temperature rise to 2 degrees, they projected that extinction rates would range from about 4 per cent – the natural rate – to 10 per cent.
“That’s still an awful lot of species in absolute numbers,” said Penn, noting that even absent climate change, the researchers estimated that 10 per cent to 15 per cent of species are at risk of extinction from the industrialisation of the ocean and other human-caused threats.
Nathalie Butt, a research fellow at the University of Queensland in Australia, said in an email that extinction of species even under the low-emissions model could be devastating to ocean health and fisheries.
“One big potential, and likely, impact will be the loss of ecosystem function in some marine ecosystems, and ecosystem cascading effects, even with only a small proportion of species lost,” said Butt, who studies the consequences of climate change on biodiversity and was not involved in the research.
For instance, the loss of a prey species could lead to declines in predators that regulate the health of marine ecosystems on which humans depend for food.
The paper noted that the regions of the ocean most vulnerable to climate-driven extinction are low-oxygen areas home to some of the world’s most productive fisheries.
“The projected impact of accelerating climate change on marine biota is profound, driving extinction risk higher and marine biological richness lower than has been seen in Earth’s history for the past tens of millions of years,” it concluded.
