Approaches that root national climate strategies in local actions will be essential for all countries as they develop new nationally determined contributions under the Paris Agreement. The potential impact of climate action from non-national actors in delivering higher global ambition is significant. Sub-national action in the United States provides a test for how such actions can accelerate emissions reductions. We aggregated U.S. state, city, and business commitments within an integrated assessment model to assess how a national climate strategy can be built upon non-state actions. We find that existing commitments alone could reduce emissions 25% below 2005 levels by 2030, and that enhancing actions by these actors could reduce emissions up to 37%. We show how these actions can provide a stepped-up basis for additional federal action to reduce emissions by 49%—consistent with 1.5 °C. Our analysis demonstrates sub-national actions can lead to substantial reductions and support increased national action.

Nathan E. Hultman, Leon Clarke, Carla Frisch, Kevin Kennedy, Haewon McJeon, Tom Cyrs, Pete Hansel, Paul Bodnar, Michelle Manion, Morgan R. Edwards, Ryna Cui, Christina Bowman, Jessie Lund, Michael I. Westphal, Andrew Clapper, Joel Jaeger, Arijit Sen, Jiehong Lou, Devashree Saha, Wendy Jaglom, Koben Calhoun, Kristin Igusky, James de Weese, Kareem Hammoud, J. C. Altimirano, Margaret Dennis, Chris Henderson, Gill Zwicker, John O'Neill