Climate scientists are confident that greenhouse gases are causing climate change, but it is difficult to predict the severity of future climate change or its local impacts. Unfortunately, we cannot wait for these uncertainties to be resolved before addressing the issue of climate change. Policymakers use two different strategies for setting climate policy in the face of this uncertainty: cost-benefit analysis and the precautionary principle. Although there has been much discussion of these strategies in the abstract, there has been less effort to assess them in operation.

This Article analyzes these strategies and considers their application to climate risks in four case studies: determination of the social cost of carbon, international endorsement of a 2°C ceiling on warming, the Environmental Protection Agency's endangerment finding, and the polar bear listing decision. The precautionary principle requires that feasible steps be taken to control risks in the face of uncertainty. This proposal works well in determining whether to regulate, but gives limited guidance about the appropriate level of regulation. Cost-benefit analysis of climate change is designed to determine the level of regulation, but it also encounters difficulties. Cost-benefit analysts must quantify the harm created by carbon emissions, which can be difficult because of uncertainty about the extent of the impact. Economists are also unsure how to take into account the large time-scale of climate change. Thus both approaches have their problems in practice.

There are some possible ways of combining economic analysis and the precautionary principle, but these have not yet been used in practice. In the meantime, the four case studies indicate that decision makers have managed to make reasonably defensible decisions despite the obstacles.

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