and other related instruments that attempt to weigh the potential outcomes of taking (or not taking) action using a common metric, usually dollars discounted to present values.

All of these approaches present serious drawbacks in the context of climate change. In muddling through, for instance, decisions are generally driven by immediate events and the lessons learned from one’s most recent experiences. Such an approach makes it difficult to thoughtfully consider long-term consequences of climate-related decisions. For instance, with regard to the prospect of irreversible or “tipping point” impacts, it will be too late to change course if one waits until such impacts have begun to unfold.

Analyses based on the precautionary principle or staying the course both reflect a substantial aversion to risk. In the case of the precautionary principle, the goal is to minimize risks of future adverse consequences of climate change with little regard for present costs. In the case of staying the course, the goal is to minimize the risks of incurring costs from responding to climate change with little regard for the risks of climate change. These approaches do not provide a way to decide among competing goals (e.g., minimizing risks of climate change impacts versus minimizing risks to economic growth) or to deal systematically with uncertainty.4

Cost-benefit analysis has been applied in many evaluations of climate change policy5 and can provide some useful insights in some contexts. But using cost-benefit analyses as a primary basis for making climate choices is problematic for a number of reasons. Many of the costs of climate change impacts are difficult or impossible to quantify.6 The sheer diversity and extent of potential costs and benefits of climate change make it very difficult to aggregate costs. Estimates can vary widely, depending on normative judgments about risk aversion and about how to account for equity concerns across generations, social groups, and regions of the world.7 Estimating the costs of actions to address climate change, while seemingly a more tractable task, is also problematic—for instance, because the costs of emission reductions over the coming decades depend critically on the pace of technological change.8

An iterative risk management approach9 for making climate change-related decisions overcomes many of these limitations. This approach can draw upon multiple forms of input—including analyses used under precautionary principle and cost-benefit frame-works—but it is not limited to single criterion (such as risk avoidance or economic efficiency) for making choices. Iterative risk management is a system for assessing risks, identifying options that are robust across a range of possible futures, and assessing and revising those choices as new information emerges. In cases where uncertainties are substantial or risks cannot be reliably quantified, one can pursue multiple, comple-



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