A long-controversial scenario has suggested the release of massive amounts of carbon from methane hydrate frozen under the seafloor 56 million years ago caused the greatest change in global climate since a dinosaur-killing asteroid presumably hit Earth 9 million years earlier.
Earth's temperature rose by as much as 10 degrees Fahrenheit, affecting the planet for up to 150,000 years until excess carbon in the oceans and atmosphere was reabsorbed into sediment.
Many species went extinct during this so-called Paleocene-Eocene Thermal Maximum.
Now researchers at Rice University in Houston say their calculations show the controversial scenario is quite possible.
Their numbers show the amount of frozen methane hydrate buried in undersea sediments was sufficient to create the warming event.
"I've always thought of [the hydrate layer] as being like a capacitor in a circuit," Rice earth science Professor Gerald Dickens said. "It charges slowly and can release fast -- and warming is the trigger. It's possible that's happening right now."
That makes it important to understand what occurred 56 million years ago, he said. "The amount of carbon released then is on the magnitude of what humans will add to the cycle by the end of, say, 2500. Compared to the geological timescale, that's almost instant."