As bad as the more obvious effects of global warming may be (e.g., drought, rising sea levels, and the like), the less-well-known effects are the ones that could prove the most worrisome in the long run. Take frozen methane, for example. We've discussed the role of methane in climate change before -- it's 21 times more powerful a greenhouse gas than CO2, but cycles out of the atmosphere far more quickly. The major risk from methane comes from large amounts being released in a relatively short period. Such large amounts exist frozen beneath the Siberian permafrost and deep in the oceans.
RealClimate explores in some detail today just how the frozen methane could melt, and what the result could be if it does so. The situation, as RealClimate sees it, could be disastrous, but there's still a great deal more research that needs to be done. Unfortunately, the article's key points are obscured by unusually dense prose. For example:
The juiciest disaster-movie scenario would be a release of enough methane to significantly change the atmospheric concentration, on a time scale that is fast compared with the lifetime of methane.
This would generate a spike in methane concentration. For a scale of how much would be a large methane release, the amount of methane that would be required to equal the radiative forcing of doubled CO2 would be about ten times the present methane concentration. That would be disaster movie. Or, the difference between the worst case IPCC scenario and the best conceivable 'alternative scenario' by 2050 is only about 1 W/m2 mean radiative energy imbalance. A radiative forcing on that order from methane would probably make it impossible to remain below a 'dangerous' level of 2 deg above pre-industrial. I calculate here that it would take about 6 ppm of methane to get 1 W/m2 over present-day. A methane concentration of 6 ppm would be a disaster in the real world.
What this boils down to is that the warming of the atmosphere and oceans has the potential to release large amounts of now-frozen methane. If it's released slowly, the most important result would be the methane being oxidized into CO2 -- less powerful of a greenhouse gas than the methane, but lasting a lot longer in the atmosphere. If it's released quickly, the result would be much worse, much faster -- but how much worse and how much faster really depends upon the amount of frozen methane released into the atmosphere. A fast release of 10 gigatons could be enough to push atmospheric carbon concentrations to seriously dangerous levels. The oceans hold the most frozen methane ("thousands of gigatons") but these would melt very slowly under most scenarios; the permafrost methane could be released much faster, but estimates of the amount trapped in Siberia ranges from 7.5 to 400 gigatons.
This is all fairly complex, relatively uncertain, and well off the radar of most people thinking about (and worrying about) global warming. It's also a subject that could end up being at least as important as increased storm strength or climate-related global pandemics, possibly a great deal more so. It's going to be hard to make frozen methane exciting -- we're not likely to see a methane hydrate Day After Tomorrow -- but it's important for all of us who talk about changes to the climate to be aware of their potential impact.
