Earth has survived warming before. But life almost didn’t make it through
New simulation shows how climate change can cause a mass extinction
About 252 million years ago, Earth almost died.
In the oceans, 96 per cent of all species became extinct. It’s harder to determine how many terrestrial species vanished, but the loss was comparable.
This mass extinction, at the end of the Permian Period, was the worst in the planet’s history, and it happened over a few thousand years at most — the blink of a geological eye.
On Thursday, a team of scientists offered a detailed accounting of how marine life was wiped out during the PermianTriassic mass extinction. Global warming robbed the oceans of oxygen, they say, putting many species under so much stress that they died off.
And we may be repeating the process, the scientists warn. If so, then climate change is “solidly in the category of a catastrophic extinction event,” said Curtis Deutsch, an earth scientist at the University of Washington and co-author of the new study, published in the journal Science.
Researchers have long known the general outlines of Permian-Triassic cataclysm. Just before the extinctions, volcanoes in what is now Siberia erupted on a tremendous scale. The magma and lava that they belched forth produced huge amounts of carbon dioxide.
Once in the atmosphere, the gas trapped heat. Researchers estimate that the surface of the ocean warmed by about 10 C. Some researchers argue that the heat alone killed off many species. Others believe that the warmth reduced oxygen in the ocean, asphyxiating the species living there. Rocks from the mass extinction appear to have formed when at least some of the ocean was lacking oxygen.
Dr. Deutsch and Justin Penn, a graduate student, recreated the world at the end of the Permian Period with a largescale computer simulation, complete with a heat-trapping atmosphere and a circulating ocean.
As the Siberian volcanoes flooded the virtual atmosphere with carbon dioxide, the atmosphere warmed. The ocean warmed, too — and according to the model, it began losing oxygen.
Some parts lost more than others. On the surface, for example, fresh oxygen was produced by photosynthetic algae. But as the ocean warmed, its circulatory currents also slowed, the model demonstrated.
Oxygen-poor water settled to the bottom of the oceans and before long, the deep was gasping. Rising temperatures and plunging oxygen must have made huge swaths of the oceans uninhabitable. Some species survived here and there. But most disappeared completely.
“Everything was losing a lot of habitat, creating the risk of extinction,” said Dr. Deutsch. “But the risk was actually higher in places that were cold. That was a bit surprising.”
You might expect that animals near the Equator would be at a greater risk, because the water was warm to begin with. But Dr. Deutsch’s model suggested a very different kind of apocalypse.
Animals in oxygen-rich cold water could not handle the sudden drop, while those in tropical waters were already adapted to poor oxygen. And the cold-water species could not find refuge elsewhere.
The new study offers an important warning to humans over the next few centuries.
“The way the Earth system is responding now to the buildup of CO2 is in the exact same way that we’ve seen it respond in the past,” said Dr. Kump.
“Left unchecked, climate warming is putting our future on the same scale as some of the worst events in geological history,” Dr. Deutsch said.
About 252 million years ago, animals in oxygen-rich cold water could not handle the sudden temperature jump of about 10 C.