Choosing and using climate scenarios for climate impacts assessment and adaptation planning: helping users navigate the thicket

Increased concern over climate change and its impacts on human and natural systems is evidenced by the increasing priority afforded to efforts to assess climate impacts and develop adaptation strategies at a wide range of levels of governance in the United States. This is increasing the demand for climate information to inform efforts ranging from Endangered Species Act listing decisions to siting of urban wastewater treatment facilities. Scientists, resource managers and decision makers continue to face a wide variety of barriers to the effective application of climate information in planning and decision processes, including deficiencies of information, which reflect the gaps between the characteristics of available climate scenarios and users' information needs. Here we report on lessons learned from interactions with a diversity of stakeholders in the Pacific Northwest concerning their need for strategies for choosing from the dizzying array of constantly evolving projections of future climate in order to use information about climate change in analyses and planning. We propose that the choice of climate scenarios be based first on an introspective analysis of the climate sensitivity of the managed system and a consideration of management risk tolerance. This can be followed by an evaluation of the nature of available climate scenarios, including their associated uncertainty, temporal and spatial scales, and ability to simulate the parameter(s) of interest. Decisions will also need to consider the availability of technical resources for analysis (time, personnel, resource impact models). Explicitly placing the subset of climate scenarios chosen for analysis within the broader context of available climate scenarios can help eliminate the need for recursive updating of assessment results as global climate scenarios are updated over time. The implications of these strategies for communication among climate scientists, climate impacts scientists, and adaptation practitioners will also be discussed.