It’s the unknown that grabs attention.
There isn’t some huge bubble of methane waiting to erupt as soon as its roof melts.
We don’t know the total amount of methane frozen deep beneath the ocean, but we suspect it could rival the rest of fossil fuels combined. And we don’t know how much is frozen in the Arctic’s thawing permafrost and lake sediments.
We do know those methane deposits are seeping into the atmosphere, however. And the possibility of a catastrophic release is of, course, what gives methane its power over the imagination. Journalists in particular seem susceptible to doomsday predictions from such a scenario.
We have seen methane bubbling from the sea floor in the Arctic. Lakes provide an escape path for the methane by creating “thaw bulbs” in the underlying soil, and lakes are everywhere appearing and disappearing in the Arctic as the permafrost melts.
Yet so far we haven’t seen iron-clad evidence of greater methane releases due to anthropogenic warming, though such an event is certainly believable for the coming century. This brings us to the key question: What effect would a methane release have on climate?
The impact depends on whether methane is released all at once or in an ongoing, sustained manner.
Let’s pick the most likely scenario: A slow ongoing release.
Methane is a powerful greenhouse gas, trapping 72 times the amount of heat per molecule in the short term compared to carbon dioxide but “burning” to CO2 in the atmosphere in about a decade. We suspect large stores of methane, known as methane hydrates, lie frozen at the bottom of ever-warming oceans, particularly in the Arctic. On land, decomposing organic matter in thawing permafrost is another potential methane source.
I’ve modeled what happens if that methane is released continually for several decades: The atmospheric impact from methane itself only persists for about a decade beyond the methane release, whereas the extra CO2 in the atmosphere persists throughout the simulation of 100,000 years.
The possibility of a catastrophic release is more remote, but it’s a subject that, as journalists say, has legs. A submarine landslide might release a gigaton of carbon as methane, but the effect of that would be small, about equal in magnitude to – but opposite in effect of – a volcanic eruption. Detectable, perhaps, but not the end of humankind as a species.