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There is an enormous amount of methane (CH4) on earth frozen into a type of ice called methane hydrate. Hydrates can form with almost any gas and consist of a ‘cage’ of water molecules surrounding the gas. (The term ‘clathrate’ more generally describes solids consisting of gases are trapped within any kind of cage while hydrate is the specific term for when the cage is made of water molecules). There are CO2 hydrates on Mars, while on Earth most of the hydrates are filled with methane. Most of these are in sediments of the ocean, but some are associated with permafrost soils.
Methane hydrates would seem intuitively to be the most precarious of things. Methane hydrate melts if it gets too warm, and it floats in water. Methane is a powerful greenhouse gas, and it degrades to CO2, another greenhouse gas which accumulates in the atmosphere just as fossil fuel CO2 does. And there is a lot of it, possibly more than the traditional fossil fuel deposits. Conceivably, climate changes could affect these deposits. So what do we know of the disaster-movie potential of the methane hydrates?
There have been a few mentions of the ‘early anthropocene’ hypothesis recently (cf. the EPICA CO2 results, and Strange Bedfellows). We therefore welcome Bill Ruddiman to RealClimate to present his viewpoint and hopefully stimulate further discussion – gavin.
[Addendum: For a non-technical backgrounder on the 'early anthropocene' hypothesis and its significance in the context of anthropogenic climate change, see Bill Ruddiman's article "How Did Humans First Alter Global Climate?" from the March 2005 issue of "Scientific American" (first two paragraphs available for free; full article must be purchased). -mike]
Guest posting from Bill Ruddiman, University of Virginia
The hypothesis (Ruddiman, 2003) that early agriculture caused large enough emissions of greenhouse gases millennia ago to offset a natural climatic cooling remains controversial. The centerpiece of the hypothesis was a comparison of the increases of CO2 and CH4 values in Vostok ice during the current (Holocene) interglaciation versus the (natural) drops during similar portions of the three previous interglaciations. More »
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