Washington, May 29 : An ancient release of methane some 635 million years ago, which caused global warming and an ending of the last "snowball" ice age, might happen again in the future.
Research into this phenomenon was led by scientists funded by the National Science Foundation (NSF).
According to the research, an abrupt release of methane, a powerful greenhouse gas, from ice sheets that extended to Earth's low latitudes some 635 million years ago caused a dramatic shift in climate.
The shift triggered events that resulted in global warming and an ending of the last "snowball" ice age.
The researchers believe that the methane was released gradually at first and then very quickly from clathrates - methane ice that forms and stabilizes beneath ice sheets.
When the ice sheets became unstable, they collapsed, releasing pressure on the clathrates. The clathrates then began to de-gas.
"Our findings document an abrupt and catastrophic global warming that led from a very cold, seemingly stable climate state to a very warm, also stable, climate state, with no pause in between," said geologist Martin Kennedy of the University of California at Riverside (UCR), who led the research team.
According to Kennedy and colleagues, methane clathrate destabilization acted as a runaway feedback to increased global warming, and was the tipping point that ended the last snowball Earth.
The snowball Earth hypothesis posits that the Earth was covered from pole to pole in a thick sheet of ice for millions of years at a time.
"Once methane was released at low latitudes from destabilization in front of the ice sheets, warming caused other clathrates to destabilize," Kennedy said.
Not all of Earth's methane was released millions of years ago. Methane clathrates are present today in Arctic permafrost and beneath the oceans at continental margins. They will remain dormant, unless triggered by warming.
This trigger is a major concern, according to Kennedy, because it's possible that very little warming could unleash this trapped methane.
Uncovering the methane reservoir could potentially warm the Earth tens of degrees, and the mechanism could be very rapid, he added.
"What we now need to know is the sensitivity of the trigger. How much forcing does it take to move from one stable state to the other, and are we approaching something like that today with current carbon dioxide warming?" said Kennedy.
"Today, we're conducting a global-scale experiment with Earth's climate system, and witnessing an unprecedented rate of warming, all with little or no knowledge of what instabilities lurk in the climate system and how they can influence life on Earth," he added.