How climate policy commitments influence energy systems and the economies of US states

In the United States, state governments have been the locus of action for addressing climate change. However, the lack of a holistic measure of state climate policy has prevented a comprehensive assessment of state policies’ effectiveness. Here, we assemble information from 25 individual policies to develop an aggregate index of state climate policies from 2000–2020. The climate policy index highlights variation between states which is difficult to assess in single policy studies. Next, we examine the environmental and economic consequences of state climate policy. A standard-deviation increase in climate policy is associated with a 5% reduction in per-capita electricity-sector CO₂ emissions and a 2% reduction in economy-wide CO₂ emissions per capita. We do not find evidence that more stringent climate policy harms states’ economies. Our results make clear the benefits of state climate policy, while showing that current state efforts are unlikely to meet the US goal under the Paris Climate Accord.