Earth's big "burp" triggered extreme global warming
Margaret Munro
CanWest News Service
http://www.canada.com/saskatoon/starphoenix/features/onlineextras/story.html?id=079b6488-79af-4540-a27e-aa3a958cda2e
Skeptics of global warming, not to mention Hollywood producers looking for plots for their next disaster movie, might want to consider what happened when the Earth let it rip 55 million years ago.
A report in the journal Nature this week suggests that a massive belch of carbon-rich methane gas from the North Atlantic triggered 200,000 years of extreme global warming.
Temperatures soared five to 10 degrees, rivers overflowed due to extraordinary rains, life in the deep ocean died off, and the face of the world was transformed as northern regions warmed and creatures like camels and primates migrated to the Americas.
Scientists say the pre-historic release from the deep could prove a dramatic analogue for what might happen if humans keep pumping massive amounts of carbon dioxide into the air.
"The case is getting stronger that global warming is associated with large hydrocarbon releases, and here's an example where it seems to have happened in the past," says Dr. Roy Hyndman, a senior scientist at the Pacific Geoscience Centre of the Geological Survey of Canada.
"If you put a lot of methane or other hydrocarbon into the atmosphere you can get abrupt and very large global warming and that's what we're doing now," says Hyndman. "The amount we are putting in now is huge in the geological context, very large."
Scientists estimate at least 1,500 gigatonnes of carbon was pumped into the atmosphere at the time of the prehistoric warming, less than the estimated 3,000 to 4,000 gigatonnes humans are expected to release over coming centuries. Man-made emissions of carbon are now released into the atmosphere at a rate of close to 6.5 gigatonnes a year.
Scientists have known for years about the massive prehistoric release because they can see the distinct chemical signature in the geological record. But until now, no one has been able to pin down where the carbon originated.
A European team, lead by Henrik Svensen at the University of Oslo, has discovered ancient "escape conduits" on the floor of the Norwegian Sea. The researchers suggest in Nature that such conduits were common throughout the Northeast Atlantic 55 million years ago as the seafloor literally ripped apart between Greenland and northern Europe.
The European scientists suggest upwellings of molten rock from deep in the Earth heated and cooked organic material in sea sediments, producing extraordinary amounts of methane gas that bubbled out into the atmosphere. Methane is 21 times more potent as a greenhouse gas than carbon dioxide.
Dr. Gerald Dickens, an earth scientist at Rice University in Texas whowrote a commentary accompanying the Nature report, says “it's the first really nice evidence that hydrocarbons were coming out of the seafloor at this time."
Dickens and Hyndman say the ancient warming event is an intriguing, if not yet completely solid, analogue for what humans are doing to the atmosphere today.
"The question is will it just warm steadily as we add more and more carbon, or is there some point where it will warm a lot," says Hyndman. He studies gas hydrates on the seafloor that might be released as the globe warms, triggering even faster warming. Huge stores of methane are trapped in the hydrates under the seafloor off the coasts of Canada and other countries.
If the gas in the hydrates are released, scientists predict that temperatures would soar because methane is such a potent greenhouse gas.
"There is a danger of a sudden or catastrophic big change," says Hyndman.