April 2017 - In May 2015, the Principals of the Subcommittee on Global Change Research made the decision to use the full range of IPCC RCPs and CMIP5 products for physical climate science analyses in the NCA4. 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.