Developing Scenarios of Change
Scenarios are plausible alternative futures, each describing what might happen under a range of possible assumptions about policy decisions and the behavior of the Earth system. By illustrating possible future conditions, scenarios provide a basis for analyzing the potential impacts of and responses to global change. USGCRP is working to develop scenarios of change for the United States that can feed into the sustained-assessment process and support the needs of both scientists and stakeholders, focused on population, demographics, land-use change, sea-level rise and coastal flood risk, and climate change.
Population, demographics, and land-use change: Changes in future population and land use have the potential to affect—and be affected by—climate change. In 2015, USGCRP convened two workshops on developing demographic and land-use scenarios for the United States. Modelers and scenario users convened to identify critical uncertainties in projections; key natural, socioeconomic, and policy variables to consider; and capabilities (or gaps therein) to produce long-term projections for future research and decision-support needs. USGCRP is coordinating the development of U.S. population scenarios using Integrated Climate and Land-Use Scenarios (ICLUS), a suite of models representing demography, migration, and spatial allocation of housing that are consistent with the Shared Socioeconomic Pathways, a set of possible development pathways used by the climate-change-research community to standardize analyses. The use of ICLUS v2 allows the exploration of a range of development pathways, improving the ability to understand climate-change impacts, vulnerability, and mitigation and adaptation options.
Sea-level rise: In 2015, at the request of the White House Council on Climate Preparedness and Resilience, USGCRP and the National Ocean Council convened an interagency task force to develop consistent, accessible, authoritative, and regionally-appropriate scenarios of future sea-level rise and coastal-flood hazard for the United States, and to integrate these scenarios into existing Federal tools and capabilities for supporting preparedness planning. These scenarios are intended to serve as a starting point for coastal preparedness planning and risk-management processes and provide a basis for assessing societal and ecological risks associated with sea-level rise in the Fourth National Climate Assessment (NCA4). The task force is developing regional-scale scenarios for the entire U.S. coastline based on the global scenarios developed for the Third National Climate Assessment (NCA3), accounting for key determinants of local variability in sea-level rise. The task force is also developing scenarios of extreme-water levels associated with these sea-level rise scenarios. Participating agencies are working to integrate these scenarios with existing tools and approaches useful to communities and stakeholders, such as floodplain mapping and visualization, flood-elevation engineering tools, and tools for estimating the future extent of coastal erosion. Participating agencies include USGS, U.S. Army Corps of Engineers, FEMA, NOAA, EPA, and NASA.
Climate change: In May 2015, USGCRP released a memo entitled “U.S. Global Change Research Program General Decisions Regarding Climate-Related Scenarios for Framing NCA4”, signaling to the climate change and impacts scientific communities that NCA4 would base its climate scenario development on the IPCC Representative Concentration Pathways and Coupled Model Intercomparison Project Phase 5 ensemble of model runs. Subsequently, USGCRP is developing and implementing an overall strategy for developing authoritative, relevant, and accessible climate-change scenarios for NCA4 and the Sustained Assessment. Participating agencies include NASA, NOAA, DOE, the Bureau of Reclamation, USGS, U.S. Army Corps of Engineers, EPA, and the Office of Science and Technology Policy.
These efforts are focused on the development of scenario products, and accompanying guidance, for NCA4 author teams and for Federal, state, tribal, and local users in need of scenarios to support their planning and decision making. Scenarios are based on aspects of the U.S. climate most relevant for assessing key societal risks, such as changes in the frequency and intensity of weather and climate extremes, and attempt to characterize these risk-relevant climate changes in the face of current scientific uncertainties.