May 2015 - The U.S. Global Change Research Program’s Decisions Regarding Climate-Related Scenarios for Framing the Fourth National Climate Assessment are now available. USGCRP is announcing these decisions to provide researchers with the time needed to incorporate these scenarios into studies relevant for the Fourth NCA (due in 2018) and to give user groups an early signal of the direction of the next NCA.
For physical climate science analyses, NCA4 will use the full range of IPCC RCPs and CMIP5 products. For assessments of impacts, vulnerability, and adaptation responses, NCA4 will focus on RCP 8.5 as a high- end scenario and RCP 4.5 as a low-end scenario. Other scenarios (e.g., RCP 2.6) may be used in addition where instructive, such as in analyses of mitigation issues. The use of RCPs 8.5 and RCP 4.5 as core scenarios is generally consistent with the range of emission scenarios used in the Third National Climate Assessment (NCA3). This memo provides more detailed information.