Impacts of National Decarbonization Targets for Subnational Societal Priorities

Carbon mitigation has well-recognized linkages with other environmental and socioeconomic priorities, such as air pollution, economic development, employment, etc. While climate change is a global issue, many other societal priorities are local concerns. Since local efforts form the pillars of achieving co-benefits and avoiding dis-benefits at the national level, it is critical to go beyond national-level analyses and focus on the synergies and tradeoffs at the subnational level. Here we use the United States as an example to evaluate the impacts of mid-century national-level deep decarbonization target for state-level societal priorities. Based on the Global Change Assessment Model with state-level details for the US (GCAM-USA), we design two mid-century scenarios: A Reference scenario that assumes the U.S. undertakes no additional climate mitigation policy, and a Deep Decarbonization Scenario that assumes the U.S. achieves the NDC goal through 2025 (26-28% reduction relative to 2005 levels) and then follows a straight-line trajectory to 80% reductions in economy-wide GHG emissions by 2050 relative to 2005. We then compare these two scenarios for a variety of metrics of carbon mitigation and other societal priorities in 2050. We highlight two findings. First, the synergies and tradeoffs of carbon mitigation with other societal goals at the subnational level can be quite different from the national level. For example, while deep decarbonization could improve national energy security by reducing the overall dependence on energy imports, it may exacerbate energy independence goals for some states by increasing inter-state electricity imports. Second, achieving national-level decarbonization target could result in unequal regional impacts across states. We find uneven geographic impacts for air pollution (more co-reductions occur in the eastern states), economic costs (energy prices increase more in the northeastern states) and employment (jobs increase in the western states where renewable capacity scales up, and decrease in the northeast due to reduced mining activities). Therefore, local decision makers may find decarbonization in line or contradicting with the most urgent local priority to address, highlighting the importance of evaluating the synergies and tradeoffs at the subnational level.