Another feedback. It's not negative, I'm positive

[Vergent]

http://qz.com/108534/the-one-thing-nature-did-to-fight-climate-change-is-no-longer-working/

[wili]

Thanks for that link, V. I first saw that phenomenon, of trees actually exuding CO2 instead of (net) taking it in, at minute 40 of the video:

http://channel.nationalgeographic.com/channel/videos/six-degrees-could-change-the-world/

Interesting (and terrifying) as this development is, I wonder if we might expand this to a discussion of all major feedbacks (perhaps mostly to the exclusion of the possible rapid release of sub-sea methane hydrates, which is already the subject of vigorous debate on a neighboring thread)?

[ccgwebmaster]

Thanks for that link, V. I first saw that phenomenon, of trees actually exuding CO2 instead of (net) taking it in, at minute 40 of the video:

Just to ask the obvious question - how can a tree net exude carbon dioxide for any prolonged length of time without... dying? I understand they store a certain amount of energy they can metabolise in this way, but don't see how it could be sustained over an extensive period of time - that notion seems somewhat contrary to my mental picture of how trees work.

A dead or burned tree will continue to release carbon dioxide, of course.

Interesting (and terrifying) as this development is, I wonder if we might expand this to a discussion of all major feedbacks (perhaps mostly to the exclusion of the possible rapid release of sub-sea methane hydrates, which is already the subject of vigorous debate on a neighboring thread)?

With 1 in 100 droughts in 2005 and 2010 and substantial associated tree mortality, I think the Amazon is already starting to look shaky, notwithstanding IPCC forecasts that it wouldn't die back or burn down until later in the century. I think it alone is good for adding another ~110ppm carbon dioxide - but that's off the top of my head, so corrections welcomed.

Other forest systems now exposed to pests (pine beetles) and drought and fire above historic norms may well contribute significant additional amounts too (the Amazon isn't the only place likely to go away).

Plus land based permafrost - microbial activity counters the methane far more effectively here than in shallow seabed, but still an awful lot of carbon dioxide waiting to come out to play. The recent Vaks paper suggested 1.5C warming for widespread deterioration of permafrost (well within currently committed climate outcomes) but I would argue there is already widespead signs of permafrost decay - it'll just be an awful lot worse by 1.5C (indeed, deep enough to influence the caves they used to assess what was happening).

What are your criteria for major? Both of the above feedbacks (and the clathrates) have the potential to add more greenhouse gas than the total historic human contribution still resident in the atmosphere, if I understand them right.

[wili]

Thanks for the insights, ccg.

Of course you're right that sea bed methane and permafrost melt are the big kahunas as far as potential for massive feedback.

But there are so many others at play and it seems like no one is even trying to tally them all up, much less try to figure out how they might interact.

I think it is always possible to look at just one of these and say--oh, that might not develop very quickly, or perhaps there will be some countervailing process that will minimize it. And all of those possibilities should be carefully considered.

But we are talking about a whole globe here, one full of all sorts of processes that all feedback on each other.

I don't have a set definition of "major" feedback. It may be too premature to even try to make such a distinction. I guess I meant that for now we don't have to considered feedbacks that have very limited carbon stored and so won't likely play a major role on the global scale, even if some will be locally devastating.

It seems like it is exactly in blogs like this that we can bring collective expertise and interests together to try to see bigger pictures, beyond just the Arctic, or beyond just individual feedbacks.

Just a though, though. I posted a shortish list of what I considered potentially major feedback on the other thread. That might be a good place to start. Maybe I will go ahead and start a separate thread for them.

But any further thoughts, suggestions, insights would be most welcome.