I should add that the point of thinking of this as a decision under uncertainty, is that it partially cuts through the political games. If someone came up with a believable policy that would cut greenhouse gas emissions by 90% and cost only 10 million dollars, then everyone ought to support that policy who thinks that there is a non-negligible chance that the AGW thesis is true. (and from what I gather, everyone should believe that there is a non-negligible chance that the AGW thesis is true). I don't know what the level of certainty or the cost should have to be for accepting any particular policy proposal. But being in principle opposed to spending money on greenhouse gas reduction, (or conversely being in principle committed to spending whatever it takes to cut emissions) is not a tenable position. I get the impression from certain right wing pundits that this is the stance they have taken, or at least the eye-rolling behavior every time global climate change gets mentioned indicates as much.