We are especially grateful to Walter Short who first envisioned and developed the WinDS and ReEDS models. We also thank the NREL analysts who provided input on the technology costs, assumptions, and methodologies in ReEDS, including

Improved air quality and human health are often discussed as "co-benefits" of mitigating climate change, yet they are rarely considered when designing or implementing climate policies. We analyze the implications of integrating health and climate when determining the best locations for replacing power plants with new wind, solar, or natural gas to meet a CO 2 reduction target in the United States. We employ a capacity expansion model with integrated assessment of climate and health damages, comparing portfolios optimized for benefits to climate alone or both health and climate. The model estimates county-level health damages and accounts for uncertainty by using a range of air quality models (AP3, EASIUR, and InMAP) and concentration−response functions (American Cancer Society and Harvard Six Cities). We find that reducing CO 2 by 30% yields $21−68 billion in annual health benefits, with an additional $9−36 billion possible when co-optimizing for climate and health benefits. Additional benefits accrue from prioritizing emissions reductions in counties with high population exposure. Total health benefits equal or exceed climate benefits across a wide range of modeling assumptions. Our results demonstrate the value of considering health in climate policy design and the need for interstate cooperation to achieve additional health benefits equitably.

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 100% Clean Electricity by 2035 ScenariosWe evaluated four main 100% clean electricity scenarios, which were each compared to two reference scenarios: one with "current policy" electricity demand (Reference-AEO) 2 and a second with much higher load growth through accelerated demand electrification (Reference-ADE). The Reference-ADE case includes rapid replacement of fossil fuel use with low-carbon alternatives across all sectors, including electrified end uses and low-carbon fuels and feedstocks, Annual Energy Outlook (AEO) and the U.S. Long-Term Strategy (LTS) demand cases Supply-side sensitivities include renewable energy costs, storage costs, nuclear costs, electrolyzer costs, CCS cost and performance, transmission constraints, new natural gas restriction, natural gas fuel costs, expanded biomass supply, low-cost geothermal, and allowing DAC in the Infrastructure Renaissance and Constrained cases. xvThis report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.14 Given the reduction in motor gasoline and diesel fuels in the transportation sector under the ADE and LTS scenarios, this demand would likely decline over time. Hydrogen production to serve these needs is also expected to transition to lower-emissions pathways given the overall economywide decarbonization trajectory modeled under the scenarios. These dynamics are not modeled explicitly in our analysis.

Despite several decades of declining emissions, the health costs of particulate matter (PM2.5) in the US remain substantial, with more than $1 trillion in annual damages. We analyze the inter-county impacts of PM2.5 for 2008, 2011, and 2014 and find that even though emissions from point sources have fallen over this period, the share of PM2.5 attributable to pollution transported across county and state boundaries is still considerable in many localities. Importantly, the benefits of reduced emissions are not uniformly distributed nationwide, with 26% of counties—concentrated in the South, Midwest, and Pacific Northwest—experiencing worsening health damages since 2008. Around 30% of all US counties receive 90% of their health damages from emissions in other counties, and these damage-importing counties also tend to have lower median incomes. Our results support continued state and federal cooperation to meet air quality standards and reduce the damages caused by PM2.5 from transported air pollution.

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