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Which RCP (emissions) scenarios should I use in my analysis?

Representative concentration pathways (RCP) portray possible future greenhouse gas and aerosol emissions scenarios. RCP scenarios are not specific policies, demographics, or economic futures; instead, they are defined by total solar radiative forcing by 2100. To address uncertainty in future concentrations of greenhouse gases and emissions of aerosols, data made available via Cal-Adapt incorporates two RCPs: RCP 4.5 and RCP 8.5.

RCP 4.5 is described by the Intergovernmental Panel on Climate Change (IPCC) as a moderate scenario in which emissions peak around 2040 and then decline. RCP 8.5 is the highest baseline emissions scenario in which emissions continue to rise throughout the twenty-first century. Therefore, climate change projected under RCP 8.5 will typically be more severe than under RCP 4.5. Both RCP 4.5 and RCP 8.5 scenarios are displayed in Cal-Adapt’s tools, allowing users to assess emissions-dependent variability and evaluate a moderate scenario alongside a worst-case scenario.

The Governor’s Office of Planning and Research (OPR) recommends that agencies use RCP 8.5 for analyses considering impacts through 2050 because there are minimal differences between emissions scenarios during the first half of the century. For analyses considering impacts beyond 2050, OPR recommends selecting warming scenarios on a case-by-case basis. For a more conservative approach to a given community element, consider using only RCP 8.5. For a less conservative approach, use both RCP 4.5 and RCP 8.5. Which approach will be most useful in selecting emissions scenarios depends on a given community element’s risk. You should work with each RCP scenario separately, rather than aggregating or averaging values across RCP scenarios. Think of each RCP scenario as a distinct possible future.

For more details on scenarios, see either the Get Started page on emissions scenarios or read:

Pierce, D. W., J. F. Kalansky, and D. R. Cayan, (Scripps Institution of Oceanography). 2018. Climate, Drought, and Sea Level Rise Scenarios for the Fourth California Climate Assessment. California’s Fourth Climate Change Assessment, California Energy Commission. Publication Number: CNRA-CEC-2018-006.