Right after Trump was elected president of the United States in 2016, the Environmental Protection Agency (EPA) Administrator Scott Pruitt pledged to reexamine landmark environmental policies and repeal regulations. In their view, excessive regulations harm the US industry, and thus, reducing regulations would be suitable for businesses. On June 12, 2018, with my colleague David Cutler, a health economist at Harvard, we published a short article where we quantified and summarised the possible adverse health impacts of repealing environmental regulations. You can read the details here. For example, the EPA’s 2017 Regulatory Impact Analysis estimated that repealing the Clean Power Plants (CPP) would result in 280,000–318,000 additional short tons of SO₂ emissions and 278,000–282,000 additional short tons of NOₓ emissions by 2030 compared to CPP implementation. These pollutants are key precursors to PM₂.₅. In my report with Professor Cutler, we estimated that this resulted in increased exposure to PM2.5, which would cause an estimated 36,0000 extra deaths over a decade and an estimated 639,999 cases of respiratory ailments in children over a decade.

This is now happening again. On March 12, 2025, the EPA announced dozens of environmental regulations it plans to target. Its new administrator, Lee Zeldin, announced plans to target more than two dozen rules and policies on what the agency called the “most consequential day of deregulation in U.S. history.” The EPA didn’t provide details about what it wants to do with the regulations — whether it will try to weaken them or eliminate them. In most cases, the agency said it is reconsidering rules that apply to climate pollution from vehicles and power plants, wastewater from coal plants, and air pollution from the energy and manufacturing sectors.

Repealing today’s regulations would exacerbate pollution-related health crises more severely than in 2015, as climate change accelerates and extreme weather events (such as heat waves, tropical cyclones, and wildfires) are occurring more often and are becoming more severe. The adverse impact on public health from this second attempt to repeal key environmental regulations would be the same or even worse than the first attempt. We are now even more susceptible to the adverse health impact of air pollution because of COVID. This is likely due to increased inflammation: COVID-19 and air pollution can cause systemic inflammation in the body. Those who have recovered from COVID-19 may have residual inflammation, which could be exacerbated by exposure to air pollutants. And we are now breathing even more toxic pollution compared to 2016 due to the more intense wildfires, Indeed, there is substantial peer-reviewed scientific evidence indicating increased frequency and intensity of wildfires, heatwaves, and tropical cyclones over the past decade, with climate change identified as a key driver. For example, a 2023 study found that summer burned areas in California increased fivefold from 1996 to 2021 compared to 1971 to 1995. Wildfires in the U.S. now account for up to 25% of PM₂.₅ pollution nationally and 50% in some western regions, driven by quadrupled burned areas since the 1980s. The horrific and recent wildfires in Los Angeles that began in early January 2025 killed 29 people, destroyed more than 16,000 structures, and exposed millions to toxic smoke. In an unprecedented collective scientific effort to understand wildfires’ short- and long-term health impacts, researchers from four universities have launched a 10-year study of the Los Angeles fires.

Two rules raised particular concerns from a public health perspective. The first would be the repeal of the Clean Air Act (CAA). The CAA has been the cornerstone of U.S. air quality regulation since 1970. It grants the EPA the authority to set National Ambient Air Quality Standards (NAAQS) for six key pollutants: PM₂.₅, ozone, NO₂, SO₂, CO, and lead. Over the past five decades, implementing CAA regulations has substantially reduced air pollution, improved respiratory and cardiovascular health, and increased life expectancy. On February 7, 2024, the EPA lowered the annual PM₂.₅ standard from 12.0 μg/m³ to 9.0 μg/m³ in response to growing epidemiological evidence linking even low levels of PM₂.₅ exposure to premature mortality and cardiovascular disease. This revision is projected to prevent 4,500 premature deaths per year by 2032 while reducing asthma exacerbations, hospital admissions, and lost workdays.