A Framework for Developing Adaptation Plans
Many analysts recommend using past extreme events as an indicator of the range of risks to prepare for and of the key vulnerabilities of existing systems. They call for planners to develop vulnerability indices that rely on known dangers and hotspots (EEA 2005). This may be a good first step, based on the relatively strong certainty that the frequency of extreme events will increase. However, because climate projections suggest an increase in the intensity, not just frequency, of extreme events (such as worse floods, droughts, or storms), protecting against known dangers is not enough. And changing averages must be considered, which may alter whether something should be built or how something should be managed. For example: Will there be enough water for a hydroelectric power plant? Decision makers will have to choose between competing options, with trade-offs between current costs and potential averted damages. Moreover, they must choose in a context of uncertainty about the probability and magnitude of the changes against which these options are to protect. Climate variability is nothing new, but uncertainty has increased. The probability distributions of extreme weather events are changing, and the extent and speed of this change are unknown. So-called 1,000-year floods (floods of such magnitude that they generally happen only once every 1,000 years) may now be 100-year floods. Such events have become unpredictable, as they no longer follow a known probabilistic pattern.13 Decisions about long-lived infrastructure also must take changing averages into account. Unknown probability implies that traditional cost-benefit analysis or maximum expected value approaches (such as minimax and maximin) cannot be used. The use of subjective probabilities (such as expert opinions) continues to be an object of research (see UKCIP 2003 for an overview). In addition, the possibility of major irreversible events or “unacceptable risks” may imply that cost-effectiveness analysis for a given level of risk is more relevant.14 In other words, the best approach might be to determine what is the socially acceptable level of risk, and then to identify the most cost-effective measures to achieve this level. Multicriteria analysis—which complements techniques that rely on criteria expressed solely in monetary terms—can help to distinguish acceptable from unacceptable options (UKCIP 2003). A focus on “robust strategies”—robust in the face of an unpredictable future (Lempert and Schlesinger 2000)—is well suited for dealing with unknown probabilities. This means answering the question: What actions should we take given that we cannot predict the future? as opposed to What is the best strategy given that we expect a particular state of the world to occur? Climate change policy then becomes a contingency problem rather than an optimization problem.
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