State-led climate action can cut emissions at near-federal costs but favors different technologies

In the absence of comprehensive federal greenhouse gas mitigation policy, state-led strategies may play a pivotal role, particularly following the 2024 United States presidential election. Using a detailed energy system optimization model, we examine the outcomes of 23 climate-minded states pursuing net-zero emissions targets compared to a federal carbon cap achieving equivalent CO₂-eq reductions. Here we show that state-led decarbonization results in distinct technology choices, a 0.7% increase in system costs, and nationwide emissions reduction of 46% - substantial, but insufficient for ambitious climate goals. This pathway relies more on electrification, with 952 terawatt-hours more generation in 2050, reallocating 17.2% of emissions to the power sector. Some regions favor solar, wind, and storage, while direct air capture emerges as critical, particularly in California and the Northeast. Inter-regional trading supports and complicates mitigation efforts, underscoring the need for careful policy design. Overall, our findings highlight how state-led and federal decarbonization approaches can yield differing energy portfolios to achieve similar emissions reductions.