“I’m very concerned that we’re near the threshold and we’re going to see the tipping point in 20 years,” Kennedy warns. Temperature increases in the Arctic of a just few degrees could unleash the huge storehouse of methane, which some have estimated would be comparable to burning all recoverable stocks of coal, oil, and natural gas.

Kennedy’s Nature article bases his warnings on a long-ago event. Sediment samples gathered in south Australia led Kennedy’s

What concerns some scientists is evidence from past geological eras that sudden releases of methane have triggered runaway cycles of climate upheaval.

team to theorize that a catastrophic era of global warming was triggered some millions of years ago by a gradual — and then abrupt — release of methane from frozen soils, bringing an end to “Snowball Earth,” when the entire planet was encrusted in ice. He sees similarities in the mounting threats of thawing terrestrial and marine permafrost today. The question, he asks, is what will set the process in motion and when.

http://e360.yale.edu/content/feature.msp?id=2081