Let’s suppose that the Arctic started to degas methane 100 times faster than it is today. I just made that number up trying to come up with a blow-the-doors-off surprise, something like the ozone hole. We ran the numbers to get an idea of how the climate impact of an Arctic Methane Nasty Surprise would stack up to that from Business-as-Usual rising CO2.
Walter et al (2007) says that Arctic lakes are 10% of natural global emissions, or about 5% of total emissions. I believe that was considered to be remarkably high at the time but let’s take it as a given, and representing the Arctic as a whole. If the number of lakes or their bubbling intensity suddenly increased by a factor of 100, and it persisted this way for 100 years, it would come to about 200 Gton of carbon emission, which is on the same scale as our entire fossil fuel emission so far (300 Gton C), or roughly the amount of traditional reserves of natural gas (although I’m not sure where estimates are since fracking) or petroleum. It would be a whopper of a surprise.
Scaling Walter’s Arctic lake emission rates up by a factor of 100 would increase the overall emission rate, natural and anthropogenic, by about a factor of 5 from where it is today. The weak leverage is because the high latitudes are a small source today relative to tropical wetlands and anthropogenic sources, so they have to grow a lot before they make much difference to the sum of all sources.
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