A new paper published appearing Thursday in the prestigious scientific journal Nature presents the worst-case scenario for runaway climate change that could leave the Earth entirely ice-free within a generation.

If global temperatures continue to rise, massive amounts of methane gas could be released from the 10,000 gigaton reserves of frozen methane that are currently locked in the world's deep oceans and permafrost. Passing this climate tipping point would result in global warming that would be far worse and more rapid than scientists' current estimates.

The new paper suggests that exactly this type of cascading release of methane reserves rapidly warmed the Earth 635 million years ago, replacing an

Ice Age with a period of tropical heat. The study's lead author suggests it could happen again, and fast – not over thousands or millions of years, but possibly within a century.

"This is a major concern because it’s possible that only a little warming can unleash this trapped methane," Martin Kennedy, a professor at UC Riverside, said in a release. "Unzippering the methane reservoir could potentially warm the Earth tens of degrees, and the mechanism could be geologically very rapid."

Methane is 25 times more potent than carbon dioxide as a greenhouse gas. And the frozen reserve is twice as large, by volume, as the world's known fossil fuel reserves.

Climate projections, like those produced by the Nobel Prize-winning Intergovernmental Panel on Climate Change, usually look like smooth lines moving up steadily along with carbon dioxide levels, which is a reflection of the linear mathematical models that underpin the graphs. But Kennedy and other geologists, while accepting the importance of anthropogenic greenhouse gas emissions, say that standard climate models can't account for massive climate changes that occur within decades.

"None of this stuff is linear. It's non-linear," Kennedy said.

Kennedy's work in Nature examined a rapid period of deglaciation that occurred 635 million years ago looking for the "trigger" to the explosion of warming across the globe that occurred.

In his study's scenario, methane frozen with water in what's known as a "clathrate" (or gas hydrate) became destabilized at lower latitudes and began to release methane gas. The warming induced by this gas started a cascade of clathrate destabilization running up toward the poles, acting as a runaway feedback mechanism that rapidly changed the earth's climate from glacial to tropical.

Kennedy chose the period known as the Marinoan deglaciation because he sees parallels from that distant event with the rapid rise in temperatures the Earth is now experiencing due to increased so-called radiative forcing from higher levels of greenhouse gases.

"What's going to happen if we double or triple CO2 levels?" he said.

In our world now, clathrates exist in Arctic permafrost and in the ocean near the continents. The professor worries that rising CO2 levels could drive enough warming to destabilize the Earth's clathrate reserves. Based on his analysis of the geological record, that could lead to climate change that is more rapid than most scientists imagine and that would prove difficult for humanity to cope with.

"If the Earth is going to move to a new state, it will do it very rapidly," Kennedy said.

Other geologists share his worry. Jim Kennett, a professor of geology and paleobiology at UC Santa Barbara, said that finding climate triggers and tipping points had become the most important scientific problem of our time.

"Martin Kennedy's work is really important and I think he's on the right track," Kennett said.

Kennett, like Kennedy, argues that the release of methane from clathrates is the only possible trigger for massive climate change over the course of mere decades.

But not all scientists accept that methane ice is a major threat to the climate. Larry Smith, a professor in UCLA's department of earth and space sciences, said that earlier research had allayed many of the fears that methane clathrates would destabilize and release their methane.

"The requirements to destabilize the clathrates didn't seem realistic under likely future scenarios," Smith said.

David Archer, a University of Chicago geosciences professor, argued in a paper (.pdf) last year that methane release appears likely to be "chronic rather than catastrophic" and only on the scale of human fossil-fuel combustion.

Many scientists believe that a variety of other factors, like changes in the albedo (reflectivity) of the Earth could account for the massive, quick climate changes that have occurred through history.

Determining which theory is correct could have a major impact on both research priorities and policy decisions. If Kennedy is right, then rising temperatures in the northern latitudes where permafrost exists would be a very bad sign for the earth's climate.

Indeed, Larry Smith, an expert in permafrost, noted that permafrost temperatures are continuing to rise across the Northern Hemisphere. That led the UN to warn earlier this year that clathrates are a major climate wild card. Last month, Russian scientists presented evidence that the destabilization of hydrates is already occurring in the Arctic Ocean.

Still, the lack of good data on the amount of methane entering the atmosphere from warming permafrost and ocean sources prevents the sort of quantification that drives governments to take notice and change course.

"Methane seeping from permafrost is something that's occurring," Kennedy said. "The challenge with it today is that we can't measure it, so we're just blithely ignoring it."

Image: Courtesy the US Geological Survey. The map shows where clathrates are found across the world.

*J**ournal Citation: Nature Vol 453 | 29 May 2008 | doi:10.1038/nature06961 *