30 may 2008

Science Briefing: Ice age ‘trigger’
By Clive Cookson

Financial Times May 30 2008

Ice age ‘trigger’ threatens climate

The climate could be even more vulnerable to the release of greenhouse gases than scientists thought, according to a report in the journal Nature.

The most severe ice age in history, a period of total glaciation known as Snowball Earth, ended suddenly 635m years ago when large amounts of methane were released from areas of permafrost.

Each methane molecule is 30 times more potent as a greenhouse gas than carbon dioxide, though methane has caused less global warming so far because it is much less abundant in the atmosphere than carbon dioxide.

That could change if vast quantities of methane are released from frozen deposits called “clathrates”, say geologists at the University of California, Riverside.

Martin Kennedy and colleagues analysed hundreds of samples of ancient marine sediments from south Australia. They concluded that the vast ice sheets covering the planet 635m years ago started to emit clathrates when changes in pressure made them unstable and this led to a runaway greenhouse effect.

“Our findings document an abrupt and catastrophic global warming,” said Prof Kennedy. “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?”

Clathrates exist in large quantities in Arctic permafrost and, under great pressure, beneath oceans.


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