Yes, that was an interesting rather counter-intuitive finding about the reduced effect of permafrost thaw under McDougal et al's model under RCP 8.5.
But really, if we do go that path, the amount that permafrost is contributing will be the least of our worries.
Similarly, by the time we reach methane levels where the saturation feedback becomes relevant, we will already be pretty much toast.
So while these factors are interesting scientifically, they don't help us much in imagining a viable future under worst case scenarios. (Though they do suggest that it will be difficult for the climate to undergo such extreme runaway warming that it approaches Venus levels, for example--some comfort in that, I suppose).
Also note that, iirc, even the Shur paper only considered methane levels at 3% of the total permafrost carbon emissions. The recent study on Methanoflorens microbes seems to suggest that there are a lot more methanogens in thawing permafrost than previously assumed (though I haven't been able to peruse the entire article yet, so I may be off here).
More importantly, the McDougal study, important as it is for at least trying to include some 'slow' carbon feedbacks, also:
>does not include permafrost deeper that three meters (it can be about a mile deep in places), >doesn't include free methane pools that exist at deeper levels,
>doesn't include deposits under ice sheets that will be more and more exposed,
>doesn't include coastal erosion,
>and doesn't include non-terrestrial, sea bed methane sources.
Add all these in and it is clear that we have further heating and higher GHG levels in store for us in future decades and centuries even if we stop all further GHG emissions today (or really, last year). That's why we really don't have any more time--talk of a 'carbon budget' by some is just daft--we're way overdrawn on that account already.
Good point about the boiling frog problem. We do indeed have to move rapidly from an economy that emits carbon to one that actually draws down atmospheric carbon levels. In some ways, this just involves changing the rules of the game (and perhaps changing the stories in our heads about what gives our lives value). But in actuality, such rule changes (and story changes) are beyond revolutionary.
But then, revolutions do happen on occasion.
ETA: And yes, the only thing that worries me more than sudden, massive methane release is the probably more likely slower but inevitable release of all that carbon over centuries to millennia...that would ensure that our initial warming lasts millennia to millions of years longer than it would have otherwise, damning yet more species to certain extinction and probably delaying the period for any potential recovery of complex life on earth, if that ever even has a chance to happen.
