The Hot Zone

Bull in China Shop

Posted by Alison Hawkes on March 6, 2010
Category : Climate Science and Scientists, The Oceans

By Alison Hawkes

Methane first came to the world’s attention in relation to global warming in the form of a snicker. Flatulating cattle were what we were supposed to fearful of? Vegetarians cited it as proof that a meat obsessed diet was ruining the planet, while almost everyone else with a sense of humor paused and then returned to worrying about seemingly more serious sources of greenhouse gas emissions.

But this week attention was turned back to methane in a study published in the journal Science. Evidence of methane releases were observed coming from the permafrost under the ocean bed off northeastern Siberia. Here beneath the shallow waters of a 620 mile wide continental shelf, permafrost that had formed during the last ice age trapped large amounts of organic carbon and methane, creating a “megapool” of carbon in the shallow reservoir. Most research into Arctic methane releases has focused on land permafrost. But lead researcher Natalia Shakhova from the University of Alaska Fairbanks headed to the sea and recorded supersaturated methane in the surface waters above. The levels were 100 times higher than expected, presumably because the permafrost is melting under warmer Arctic waters.

Shakhova and her colleagues write that sea-bed permafrost is potentially more vulnerable to thawing than land-based permafrost. The average temperature of bottom seawater is 22 to 30 degrees Fahrenheit higher than the surface temperature above land-based permafrost.

How scared should we be? In the case of the Eastern Siberia Arctic Shelf, the researches estimate a release of about 8 million tons of carbon a year, a small fraction of the 440 million tons in global emissions. So for the moment a methane geyser isn’t about to shoot off. “But will this persist into the future under sustained warming trends? We do not know,” wrote Martin Heimann of the Max Planck Institute in Germany in an accompanying commentary. Modeling suggests sustained releases that will build up over time.

The danger is that sea-bed permafrost and other natural sources of methane will be hard to stop once they start emitting. Human induced sources of methane – yes, cattle count in this category – can theoretically be curtailed. But set off the natural sources, which currently comprise some 40 percent of global emissions, and you’ve got a bull in a china shop. Minus, of course, the actual bull.

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