Using Emissions-Driven CESM to Investigate Carbon and Climate Responses to Mitigation and Climate Intervention Scenarios

Given the continued lack of progress on global commitments to reduce fossil fuel emissions, achieving a climate future of less than 1.5C warming may not be possible without well-assessed climate actions that include mitigation, adaptation, and restoration, as well as more controversial approaches, such as carbon dioxide removal and solar radiation modification. To provide a research platform that allows for exploration of both the climate impacts of alternative emissions pathways as well as the possible effectiveness and impacts of climate actions we have developed a new framework that utilizes the Community Earth System Model (CESM 2.1.5) with emission driven scenarios, a fully coupled carbon cycle, active fire and biogenic aerosols, and new updated ocean ecosystem capabilities. The new experimental configuration has been run for 1850 pre-industrial spin up, along with five member ensembles of historical transient simulations and a range of future projections. These simulations form the basis of the Highly Optimistic Projections Ensemble (HOPE) project which is being performed by the CESM Land Model and Biogeochemistry Working Groups (LMWG and BGCWG). These future simulations compare climate trajectories and impacts under the three CMIP6 scenarios SSP1-1.9, SSP2-4.5 and SSP3-7.0. The SSP1-1.9 scenario has not been
previously explored with CESM and allows for the investigation of the effectiveness of strong climate actions through rapid transition to renewable energy, negative emissions through bioenergy with carbon capture and storage, and global efforts to remove carbon through reforestation. The framework is also being used for the Community Climate Intervention Strategies (CCIS) ensemble project which allows for exploration of individual climate intervention activities against the SSP2-4.5 emission pathway. Finally, this new configuration is being used to explore the capabilities needed for CMIP7 modeling which is based in emission driven scenarios along with active aerosol configurations.