Yesterday, 215 scientists released a petition in Bali — site of a global confab to talk about whether and how we should talk about a future treaty to reduce greenhouse gas emissions — that “begs” the world to cut greenhouse gas emissions in half by 2050. I was quoted in an AP story on the matter to the effect that scientists are in no position to intelligently dictate such a policy. And as expected, some in the blogosphere howled.

I do not believe in leaving public policy to “guys in white coats” — in any discipline. And that’s not necessarily a proposition that vitiates against environmentally-friendly public policy. Climate scientists do not have the training to tell us whether the costs associated with reducing greenhouse gas emissions are less than, equal to, or greater than the costs of business as usual. And that’s something you would want to know before signing off on greenhouse gas emission reductions. When climate economists have explored that matter, they find little to support such emission reductions even if we accept the prognostications about the future coming out of the IPCC.

Likewise, economic calculations about the same are heavily predicated on how you feel about future costs and benefits. If you believe in valuing dollars and lives in, say, 2150 as much as you value dollars and lives today, then it’s hard to accept IPCC reports and not conclude that GHG emission cuts pass a cost-benefit test. If you apply a discount rate of, say, 3, 5, or 7 percent, then it’s hard to accept IPCC reports and not conclude that GHG emission cuts don’t pass a cost-benefit test. But how you value the future is subjective, and economists have no objectively “better” preference regarding that matter than you or I.

Many have argued that we should value our great grandchildren’s lives and money as much as we value our own. Fine — there is nothing objectively wrong with that belief. But if you do, hand in your Rawlsian membership card. That’s because you’re endorsing a policy that will transfer wealth and well-being from the relatively poor (us) to the very rich (them). That is, even if the Stern Review is correct about the economic costs of climate change, real per capita income in developing countries will be higher than that of the developed world today by 2100. Moreover, if you value the future every bit as much as you value the present — and thus embrace, say, a 0.1% discount rate — then simple math suggests you ought to be saving just about everything you earn.

I do not believe that “the experts” in any field should be dictating climate policy because there are plenty of important value judgments built in to those policies and experts however defined have no objectively better values than you or I. I do believe, however, that any serious reflection on the ethics of reducing greenhouse gas emission will find that the case for such a policy is harder to make than you might think, even if you accept what the IPCC is telling us.