Scenarios

Using Scenarios to Structure Uncertainties

Scenarios are a decision making tool that policy makers can use to model the range of possible consequences associated with particular actions or events. The European Environmental Agency explains that scenarios are "based on 'if-then' propositions" and are not intended to be used as predictions or forecasts. These stories can help decision makers explore assumptions, test hypotheses, and ultimately, develop robust strategies capable of managing the irreducible uncertainties of global environmental change. Although many types of scenarios exist (i.e., high resolution scenarios, global climate model scenarios, and analogue scenarios), scenario building typically involves the following components:

1. Identifying a decision;
2. Describing the current state of affairs;
3. Describing any changes that are likely to occur; and
4. Describing the future consequences of those changes.

Additional information is available under "Environmental Scenarios" in the Recommended Links section.

Simple Scenarios

Simple scenarios, such as those referenced in the scenario tree, can be useful in grappling with uncertainties in climate adaptation decisions. If time and information were free, it would be desirable to have complete, detailed forecasts of climate change (downscaled to an appropriate location). However, in practice the range of alternatives available in a given context are highly constrained and there may be little value of information associated with more detailed climate scenarios in selecting among these limited alternatives. Hence, simple scenarios can help and should be the first step in thinking through uncertainties for climate change.

Sockeye Salmon Climate Scenario

We recently conducted a workshop to help characterize and quantify how vulnerable sockeye salmon are to climate change in the Fraser River System. Two temperature change scenarios were employed during the event: 1) 2°C of additional warming over 60 years; and 2) 4°C of additional warming over 70 years. The 60 year period comprised 15 four-year lifecycles of sockeye salmon cohorts. These simple scenarios were deemed appropriate by the scientists participating in the workshop because they had little or no specific knowledge of how a warmer and wetter climate would affect the life cycle stages of sockeye salmon in this system.