Municipal efforts to plan for the likely impacts of climate change can best be understood as collective risk management.

Let's look at the second part of that phrase first: risk management. The only way communities can determine when, whether, and how to respond to climate change risks is to engage in long-term forecasting and impact assessment (to determine which problems are likely to occur), problem-solving (to decide what steps to take to reduce vulnerability and enhance resilience) and monitoring and revision (to continuously adapt management plans in light of new information).

Now let's return to “collective.” No single individual is empowered to make all these decisions alone. Thus, forecasting needs to be undertaken jointly, problem solving involves complex negotiations, and monitoring requires collective efforts.

These three interconnected steps—undertaken by the right people, engaged in the right processes—compose collective risk management.

Risk Assessment

In general, there are three kinds of calculations that communities have to make before they can formulate collective risk management plans. First, they have to determine the climate change-related hazards they face. Second, they have to calculate the likelihood that each of these hazards will occur. Finally, they have to estimate what the consequences or impacts will be, if and when any of these hazards occur (Kaplan and Garrick 1980).

These last two assessments can be summarized in the term “societal risk”: the probability of a hazard occurring multiplied by the magnitude of the adverse effects if it does occur. But stating societal risk in terms of a formula implies a precision that can't really be realized. Each step in the risk assessment process requires making informed estimates—and given the complexity of the ecological systems involved and the uncertainty inherent in global climate dynamics, only rough estimates are possible. Thus, the process of societal risk assessment depends on making best estimates. It also requires harmonizing or blending a wide range of political, scientific, economic and ecological considerations.