|2011-02-22 16:49:44||Prudent Risk|
I drafted up Prudent Risk for Prudent Path Week. As always, feedback is appreciated.|
That's a really good post that draws the threads together nicely.
I was confused by a couple of things, which may say more about my lack of understanding than any mis-statement on your part.
1) You say "carbon cycle feedbacks make the higher climate sensitivity values entirely plausible" Carbon cycle and other long-term feedbacks, being neglected in conventional estimates of climate sensitivity, can't argue for higher values of sensitivity in the PDFs. The carbon cycle feedbacks could certainly lead to worse outcomes but that's through increasing CO2, not changing the CO2 concentrations. This is a definition problem and I may well have it wrong.
2) You say that the skeptics "contradicted themselves by an order of magnitude. Twice!". Firstly, while it's true that they contradict themselves, it's a sign problem, not by an order of magnitude. Secondly, I don't see how they have minimized the effects of climate by an order of magnitude (ie, ten times) even once, Although it's undoubtedly true that they have grossly misrepresented uncertainty in several instances of cherry-picking and wishful thinking (I corrected my original typo of cheery-picking, which may actually be apt). My concern here is that some people could read your words as an exaggeration, implying that climate change will be one hundred times worse than the skeptics claim.
3) You mention the home/car insurance metaphor at the end. Insurance is arranged for compensation after things go wrong. What you are arguing for is for preventative measures that reduce the chance of things going wrong in the first place, like replacing the old electrical wiring in your home or fixing the brakes or steering on your car.
Thanks Andy. I think I see your point on #1 - that CO2 may increase faster than we expect, but that doesn't mean sensitivity is higher than we expect.
On #2 these are the two order of magnitude contradictions:
Aerosols - Lindzen argues the net aerosol forcing is close to zero. Well, he argues that the uncertainty is so large that the sign is unknown, as you say. But in his calculations he treats the forcing as zero, as I've previously discussed (Case Study trilogy). The NIPCC says the forcing is larger than the IPCC value, which is -1.2 W/m2. So they differ by roughly an order of magnitude (call it -0.2 vs. -2 W/m2).
Sensitivity - NIPCC puts it at around 0.3–0.5 W/m2, Idsos put it at larger than the IPCC 3 W/m2. That's an order of magnitude as well.
On #3, it's true that the insurance analogy isn't perfect. But you pay a small amount for the insurance up front. You're right that it's not preventative, but there are similarities in that they're both small up-front costs to do something about a potentially bad scenario in the future.
I'd be happy to change this if somebody could come up with a better analogy. The car brakes is a pretty good one - I might use that instead.