Wetlands in the Air
25/05/08 16:09
A study late last week suggested that atmospheric methane emissions are way up. This is disturbing on a number of levels that should have a lot of people very worried.
First, methane is a very powerful greenhouse gas, one that is not found in the same abundance as carbon dioxide but which is much more effective in capturing the sun's energy and enhancing the heat retention abilities of the atmosphere. So simply having more in the atmosphere is a bad sign in itself.
Second, paleoclimatologists have traditionally interpreted methane shifts in ice-core analyses of atmospheric composition from tiny ice bubbles (say, from Greenland or Antarctica) as a sign of the abundance and extent of wetlands globally. That is, wetlands are a major source of atmospheric methane, and when methane levels went up in the past it was often because the number of wetlands also increased. So perhaps the current increase isn't so bad? Aren't we worried about the extent of wetlands from a conservation perspective? Unfortunately, not in this case. Instead, it appears that the most likely explanation is that many wetlands that have been in effect frozen for centuries or millennia at high latitudes are defrosting. Places like Siberia and Alaska are warming quite rapidly, and these frozen peaty areas are beginning to turn into wetlands and giving up their great stores of methane. And that will make setting new emissions agreements just that much harder. The good news is that methane tends to break down in a few decades in the atmosphere. But not before potentially landing us into the next point.
The third and potentially very bad possibility: runaway climate warming, AKA the era of positive climate change feedbacks. Most climate scientists currently agree that we can probably make big reductions in our emissions now (or soon) and atmospheric greenhouse gases should level off and eventually fall, so we can avoid the worst models of climate change. But: there is a big but. The climate in the past has tended to make most big shifts rather suddenly, changing states (from A to Q) rather than gradually (1 then 2 then 3). Our models are better at showing gradual but not generally sudden change, which is a little unrealistic. So what are the mechanisms that drive sudden state-level change? One of the potential atmospherically smoking guns is methane from wetlands. In other words, the atmosphere warms a little, high-latitude frozen muck begins to warm and releases a lot of methane, which makes the atmosphere warm a lot more, which means more methane is released. This is positive feedback, and if that has begun, there's not a lot we can do in terms of climate mitigation. We can only brace ourselves.
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