A warming climate led to the biggest mass extinction in Earth's history, scientists have claimed.
Around 252 million years ago - nearly 200 million years before the dinosaurs were wiped out by an asteroid - about 96 percent of all sea life was wiped out in the 'Great Dying'.
The exact cause of it has been debated for decades, but new research from the US points the finger at global warming.
Scientists at Washington and Stanford universities ran models of the ancient Earth, simulating the effects a warming atmosphere would have on the planet.
They found once temperatures at sea level were about 10degC higher than they are today, the oceans lost 80 percent of their oxygen. This sounds bad enough, but the higher temperatures made animals' metabolisms rise - this means they required more oxygen than before, despite most of it disappearing from the water.
"The signature of that kill mechanism, climate warming and oxygen loss, is this geographic pattern that's predicted by the model and then discovered in the fossils," said author Justin Penn, a University of Washington doctoral student in oceanography.
"The agreement between the two indicates this mechanism of climate warming and oxygen loss was a primary cause of the extinction."
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The hardest-hit in the simulations were creatures living far from the tropics. This lined up with the paleontological record.
"Since tropical organisms' metabolisms were already adapted to fairly warm, lower-oxygen conditions, they could move away from the tropics and find the same conditions somewhere else," said co-author Curtis Deutsch, oceanography professor at Washington.
"But if an organism was adapted for a cold, oxygen-rich environment, then those conditions ceased to exist in the shallow oceans."
The scientists say at the current rate of warming, we'll be about 20 percent of the way towards similar conditions by the end of this century. By 2300, we could be halfway there.
"This study highlights the potential for a mass extinction arising from a similar mechanism under anthropogenic climate change," said Mr Penn.
Earlier this week, scientists said this year's carbon emissions would hit a record high, up 2.7 percent on 2017. The United States is by far the biggest emitter per person, but China emits the most overall.
The study was published on Friday (US time) in journal Science.