Scientists raise alarm over ‘dangerously fast’ growth in atmospheric methane

> a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth.

deposits of solid methane ice can exist trapped on the seafloor [1]. this is possible only at the extreme pressures of the seafloor [2].

so, on its own, a little methane in the atmosphere is not a big deal, because of the short half-life.

except, you have methane ice deposits in the ocean that can melt if the oceans get a little bit warmer.

this can enter into a fun little runaway feedback loop pretty quickly. little bit of methane melts, causing a little bit more ocean warming, causing more methane to melt, etc.

if this feedback loop were to occur, the evidence you would expect to see would be spontaneous release of methane emissions from the ocean, and you would expect it to be happening in places where the warming ocean put methane clathrates right at their melting point for that depth & pressure of seawater. which...is exactly what's happening [3]

> The study, to appear in the journal Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union, shows that of 168 bubble plumes observed within the past decade, a disproportionate number were seen at a critical depth for the stability of methane hydrates.

> "We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater has warmed," said lead author H. Paul Johnson, a UW professor of oceanography. "So it is not likely to be just emitted from the sediments; this appears to be coming from the decomposition of methane that has been frozen for thousands of years."

a similar feedback loop is possible in the Arctic tundra [4], where permafrost can melt and release trapped bubbles of gases that include methane, which in turn will warm the planet a bit and cause more permafrost to melt.

and of course the two feedback loops are able to reinforce each other, because a bit of methane released from the arctic also helps heat the oceans, and a bit of methane released by the oceans also helps melt the permafrost.

0: https://en.wikipedia.org/wiki/Methane_clathrate

1: https://en.wikipedia.org/wiki/Methane_clathrate#/media/File:...

2: https://en.wikipedia.org/wiki/File:Methane_Hydrate_phase_dia...

3: https://www.ocean.washington.edu/story/Bubble_plumes_suggest...

4: https://en.wikipedia.org/wiki/Arctic_methane_emissions

Notice that you can look at the GWP potential over time spans. For methane, over the next 100 years (which is the period that will impact most HNers the most) it is at least 20x as impactful as CO2.

The reason this matters is because the biggest unknown with climate change is positive feed backs. A classic example of this is that as the arctic has less ice it also reduces the albedo of the oceans allowing them to absorb even more heat faster.

Another, methane related, theoretical, positive feed back is methane clathrates which are essentially frozen stores of methane deep in the arctic ocean. If the ocean were to warm up enough this might rapidly release methane leading to a catastrophic runaway warming scenario, leading to what is suspected to have caused rapid climate change in the Quanternary period [1].

It is currently believed by many researchers that, in the specific case of the 'clathrate gun' firing, it is unlikely to happen. The trouble is we don't know for sure. That is just one unknown, potentially devastating positive feed back.

If you read Peter Ward's work (and some others as well) it looks like at various times in the history of the planet there was very rapid, very destructive climate change that was caused by a cascading series of positive feed backs. We don't know exactly where these are, but the more methane we release (and CO2) and the faster the planet warms the more likely we are to find these.

It is important to note also, that these positive feedbacks are not factored into the IPCC report (just like the potential collapse of Thwaites Glacier is not) because the is no way to effectively model this and make predictions about them. It means that if you think the IPCC report sounds bad (or even if you don't) there is a lot of potential risk not mentioned in the various pathways there.

1. https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis