In a comment on the post, Oliver Tickell raised the question of whether boreal forest die back might actually contribute to cooling, if only in the short term, as albedo increases [assuming snow is still falling!]. I said it would surprising if the math(s) has not already been done on this and results published in a major journal, with subsequent blog commentary at RealClimate or elsewhere. If someone knows of this, please enlighten us! [Chris Goodall, meanwhile, notes another recent paper, by Zavala et al, which finds that increase in carbon dioxide compromises plant defense against invasive insects.]
In The pine beetle and carbon cycle feedbacks, Simon Donner doesn't directly address Tickell's question but does advise, "be wary of the hyperbole. Not all positive feedbacks are made equal".
On the second potential feedback, methane hydrates, I wrote, "whether the Russians have evidence to indicate this may happen more quickly than previously thought, and so whether this is really a news story, may remain to be seen." For now, we should bear in mind what Tim Lenton has written in the note on tipping points which I cited:
Under the ocean sediments resides a large reservoir of frozen methane hydrates, perhaps of order ~10,000 PgC. As mentioned above, in the PETM warm event 55 Myr ago, a large amount of carbon may have been lost from this reservoir (and subsequently replenished). However, existing models and understanding suggest that such loss takes the form of lots of small release events rather than one big one. Hence it’s not clear it is a tipping element. Furthermore the release is estimated to occur over many thousands of years and therefore it may fall outside of the ‘ethical time horizon’ considered in present policies, even thought it could be started within the ‘political time horizon’ of this century.Still, even if both these feedbacks prove to be less significant than some fear, there remains plenty to be concerned about, both (as Mitchell Anderson mentioned in his original post) with regard to earth system sensitivities and (as Clive Bates outlines compellingly in his comment on my post) the human capacity to act effectively.
In the 31 March Guardian science podcast the science journalist Fred Pearce said he was optimistic about the human ability to tackle climate change. The technology was there, and the economics made sense, he said. But he was more pessimistic about tackling extreme poverty. And in Can democracy save the planet? (openDemocracy.net, 24 April), Johns Elikington and Lotherington are also optimistic, citing Ian Christie's suggestion of a "People's Kyoto".
Well, maybe. Clearly it is not helpful to talk and feel one's way into hopelessness. As Kenan Malik has said, "It is when we stop thinking of ourselves as conscious agents, with the capacity rationally to change the world...that we unleash the monsters." But optimism needs to come under relentles scrutiny if it is to survive in a strengthened form. See, for example, this.