Friday, December 18, 2009

Methane and uncertainty

Another one of the feedback mechanisms that introduces a level of uncertainty into existing climate models is methane gas. If significant quantities of methane are added to the atmosphere as temperatures in the high latitudes increase, the amount of warming predicted by the models may in fact, be a serious underestimate of what actually occurs.

Methane is critical because it is a greenhouse gas like CO2 but it is much more efficient at trapping radiation and transforming it into heat energy than CO2. If a little goes a long way, a lot of methane...well, you get the picture.

So how is this a feedback mechanism? There are two sources of methane that are currently locked away someplace where the atmosphere can't get at it; in permafrost and at the bottom of the Arctic Ocean. You find permafrost - literally ground that remains frozen year round - in the high latitudes because it is so consistently cold that it never completely thaws, even in the summer months. But warming temperatures are actually warming these same areas at a greater rate than warming is occurring elsewhere closer to the tropics. As temperatures begin to increase, permafrost begins to melt and release more of the methane trapped within it back to the atmosphere. This makes it warmer which acts to speed up the melting of the permafrost which makes it warmer. Positive feedback.

The other major source of methane, the Arctic Ocean, is completely unaccounted for in any of the existing climate models simply because no one is quite sure what is going to happen or how quickly it will occur. We know that it is there locked in the ocean floor and that removing the cover (Arctic sea ice) and warming water temperatures is likely to disturb it somehow...I guess we could just wait and see. The Arctic is predicted to be completely free of ice in the summer months somewhere between 2030-2060. As the water temperature increases, this methane sealed as gas hydrates by sub-bottom permafrost is likely to make them unstable, mobilize and rise to the surface. Some have described this store of methane as the largest natural source of methane.

If these gas hydrate deposits of methane indeed become unstable and contribute to the atmospheric concentration of greenhouse gases, they will dramatically increase the heat trapping potential of the atmosphere. Because this mechanism is not accounted for in the existing Global Climate Model's, forecasts of warming temperatures are in all likelihood underestimated. If warming occurs faster in the atmosphere, ancillary changes occurring in the oceans and on land will also be far greater than previously predicted. Positive feedback. Positively feedback.

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