Global climate change and the precautionary principle

The precautionary principle is promoted as a common sense approach that avoids unreasonable delays in taking action. A weak form of the precautionary principle, that action should not wait until all uncertainties are resolved, is indeed common sense and consistent with even the most elementary application of the methods of decision making under uncertainty to the climate change problem. The standard tools of decision analysis imply conclusions consistent with a weak precautionary principle of taking some action before all the evidence is in. Decision theory also reveals what the basis is for stronger recommendations from the precautionary principle, to the effect that action should be based on the most pessimistic possible interpretation of the future. This conclusion is only possible if prior beliefs are so pessimistic and so strong that they would outweigh any possible new scientific evidence.