Reposted from Richard Tol’s blog
I welcome the inquiry by the Select Committee into the Intergovernmental Panel on Climate Change. The focus of the inquiry is on Working Group I of the IPCC and its Fifth Assessment Report, neither of which are in my core areas of experience and expertise. I was a contributing author to IPCC WG1 AR3; I was a lead author in a few reports of WG2 and WG3; I am currently a convening lead author for WG2 AR5. I will therefore address only a few of the issues raised by the Select Committee.
· How effective is AR5 and the summary for policymakers in conveying what is meant by uncertainty in scientific terms ? Would a focus on risk rather than uncertainty be useful?
The agreed distinction between risk and uncertainty goes back to Knight (1921), with risk characterized by known probabilities (the throw of a dice) and uncertainty by unknown probabilities. Climate change is better described by uncertainty than by risk. In other arenas the IPCC has tried to redefine widely accepted concepts (e.g., vulnerability) which has led to endless, fruitless discussions on semantics. It would be regrettable if the IPCC would repeat this mistake with regard to risk and uncertainty.