A warming climate led to the largest 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 'Great Dying'.
The exact cause of it has been debated for decades, but new research from the US points the finger to global warming.
Scientists at Washington and Stanford universities run models of the ancient Earth, simulating the effects and warming atmosphere they would have on the planet.
They found that the 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 make animals' metabolisms rise – this means they need more oxygen than before, despite most of them disappearing from the water.
"This signature geographic pattern is predicted by the model and then discovered in the fossils," said Justin Penn, Ph.D., a Doctor of Oceanography at the University of Washington.
"The agreement between the two indicates this mechanism of climate warming and oxygen loss was a primary cause of extinction."
The hardest hit in the simulations were creatures living away 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 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 will 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 largest emitter per person, but China emits the most overall.
The study was published on Friday (US time) in the journal Science.