Kenneth Arrow In Defense of the Stern Review's Estimates

Oover at Project Syndicate (via Political Theory Daily Review):

Critics of the Stern Review don’t think serious action to limit CO2 emissions is justified, because there remains substantial uncertainty about the extent of the costs of global climate change, and because these costs will be incurred far in the future. However, I believe that Stern’s fundamental conclusion is justified: we are much better off reducing CO2 emissions substantially than risking the consequences of failing to act, even if, unlike Stern, one heavily discounts uncertainty and the future.

Two factors differentiate global climate change from other environmental problems. First, whereas most environmental insults – for example, water pollution, acid rain, or sulfur dioxide emissions – are mitigated promptly or in fairly short order when the source is cleaned up, emissions of CO2 and other trace gases remain in the atmosphere for centuries. So reducing emissions today is very valuable to humanity in the distant future.

Second, the externality is truly global in scale, because greenhouse gases travel around the world in a few days. As a result, the nation-state and its subsidiaries, the typical loci for internalizing externalities, are limited in their remedial capacity. (However, since the United States contributes about 25% of the world’s CO2 emissions, its own policy could make a large difference.)

Thus, global climate change is a public good (bad) par excellence.