Thursday, October 7, 2010

Climate Science: Prepare for Increasing Uncertainty

Environment 360, a very useful online magazine, has a new article by Fred Pearce that explains why the next IPCC assessment (AR5) will tell us that the consequences of living with climate change will be even more uncertain than they predicted back in ‘07. Part of this is due to external pressure on IPCC to express uncertainty more honestly than they have in the past, and part is the result of including more feedback processes whose magnitude, and even direction, is not well understood.

Pearce worries about the political fallout from this trend: how will the public respond to the argument that, the more science advances in this field, the less confidence there can be in any particular prediction? I agree, and I think economists are going to have to rethink how they represent the economics of climate change. Point estimates of damages (expected benefits of mitigation) become less relevant to policy as error bars widen; rather quickly, as Weitzman and others have argued, the uncertainty itself becomes the story. Mitigation needs to be seen not as an investment, justified on cost-benefit grounds, but as insurance. What price are we willing to pay to reduce the extreme risks that the next report will include as within the realm of possibility?

4 comments: said...

Weitzman's work on the serious probabiity of extreme outcomes is excellent on all this. He has been widely mentioned for this year's Nobel, and would be a good pick.

Anonymous said...

What is still missing from this discussion is the basic question - why should we believe any of their predictions? Generally in science, what they have constructed is simply an hypothesis. Their models have yet to make a single confirmed prediction. We know that global temperature is higher now than since the start of the 20th century ; what we don't know is what it will be in the future. I am now seeing predictions that we will experience colder temperatures in some part of the world than we have seen in 1000 years. Why are those predictions less compelling that the ones the IPCC is making?

Yes, if temperatures rise many degrees we could see serious problems. But we have no real reason to believe that they will.

Jimbo said...

The Arctic permafrost is melting. The Northwest Passage now exists, etc. etc. Sigh. It's the signal to noise ratio at a global level. Never mind. Anyway, to respond to Prof. Dornan's post, the predominant policy response is "no regrets", which stipulates precautionary measures to address the uncertainty that we have seen. The good thing is that these "no regrets" actions are mostly good investments anyway in a non-fossil fuel, environmentally sustainable future.

jre said...

It is a symptom of the political climate, not the physical climate, that anyone can claim (presumably with a straight face) that "[climate] models have yet to make a single confirmed prediction." The best-developed climate models have been proven right again and again in predicting the aspects of climate we care most about: large-scale temperature trends, geographic distribution of warming, sea surface temperatures and precipitation patterns. The smaller scale and more chaotic aspects of climate, such as clouds and wind patterns, need finer-grained methods -- but these are already pretty good, and getting better all the time. As noted above, phenomena such as disappearing Arctic sea ice have been predicted by climate models and serve as clear indicators of a warming planet.

The problem is not acknowledgment of uncertainty; that is an essential part of honest science. Rather, the problem is the dishonest use of uncertainty, whether out of ideology or self-interest, to foster political paralysis.