Basic Structure of Uncertainties

Even though the uncertainties may be profound and irreducible, it is still helpful to have a conceptual picture for the structure of these uncertainties in climate change choices.

All climate adaptation choices involve uncertainties about how fast and how much the climate will change, in terms of key variables such as average annual temperature, monthly precipitation and so forth. These climate uncertainties often interact with other uncertainties in other systems, such as the ecological or human response to a given level of climate change. Below is a sketch of a scenario tree (figure 3.3.a), or the basis of a probability tree, for the interaction of climate change, ecological response, and human system response.

It shows several different climate change scenarios are possible in a given location, over a given time frame (information about where and how to develop such scenarios is available in the Scenarios section of this site). These scenarios address the question of “What is the range of possibilities as to how the climate is likely to change in a given location, over a given time, given certain assumptions about societal scenarios?”

Then the figure shows that, conditional on a given climate change scenario, there are a range of ecological response scenarios that could unfold over time, depending on other key uncertainties such as land use practices, the frequency of disturbance, and other key variables. It answers the question of “What are potential ecological system responses to changing climate, conditional on a given climate scenario?” Influence diagrams are a great way to show these relationships and to help think about how uncertainties should be structured within scenarios. Hence, a given combined scenario to serve as the basis for thinking or analysis, conditional on assumptions, would include one climate change scenario and one ecological response scenario.

                                            Figure 3.3.a Scenario tree