US Methane Leaks and State Mandates Dominate Near-Term Emissions Outcomes in PyPSA-USA Sensitivity Runs

The preprint extends the open-source PyPSA-USA model to multi-sector resolution and applies global sensitivity analysis across thousands of parameter combinations. Results show system-wide climate impact remains overwhelmingly sensitive to upstream methane leakage assumptions and 20- versus 100-year GWP choices, while uncoordinated state renewable targets create localized transmission bottlenecks and cost spikes. Demand-side levers such as light-duty EV adoption and commercial heating electrification deliver the largest near-term abatement per dollar under current policy repeal scenarios.

Post-IRA repeal trajectories make the original 50-52 percent 2030 target from 2005 levels unattainable without rapid methane controls and accelerated electrification. The modeling directly links these technology shifts to reduced exposure to volatile fossil prices and lower cumulative social cost of carbon penalties through 2035.

Mainstream coverage continues to frame emissions policy as long-term targets rather than near-term methane and electrification timelines that the sensitivity runs identify as decisive. Observable climate damages from continued high-leakage pathways will register within the same congressional budget cycles now debating infrastructure funding.

Next steps require EPA methane rules with enforceable leak detection thresholds below 1 percent combined with state-level transmission planning that internalizes regional cost externalities identified in the model.