San Francisco and Santa Clara County join lawsuit challenging EPA’s rollback of landmark climate safeguards

SAN FRANCISCO (March 19, 2026) — San Francisco City Attorney David Chiu and Santa Clara County Counsel Tony LoPresti announced San Francisco and Santa Clara County have joined a broad coalition of states and local jurisdictions in filing a petition challenging the U.S. Environmental Protection Agency’s (EPA) rescission of the Endangerment Finding, which serves as the legal basis under the Clean Air Act to limit climate pollution from vehicles. The Endangerment Finding is EPA’s formal determination that greenhouse gas emissions from motor vehicles contribute to air pollution that fuels climate change and endangers public health.

Eliminating the Endangerment Finding will increase greenhouse gas emissions, intensify the climate crisis, and burden American communities already heavily impacted by pollution and climate change. The move will upend 15 years of regulatory progress and lead to serious consequences for residents, industries, natural resources, and public investments.

The Plaintiff coalition previously submitted a comment arguing that EPA’s rescission of the Endangerment Finding violates established law, U.S. Supreme Court precedent, and decades of scientific consensus confirming greenhouse gases from vehicle emissions harm public health.

“Climate change is an existential threat to humanity,” said San Francisco City Attorney David Chiu. “Rolling back the Endangerment Finding means fewer safeguards against the pollution that drives climate change and worsens air quality. This reckless and illegal move disregards decades of scientific evidence and harms communities already on the front lines of the climate crisis.”

“The Trump Administration has once again endangered the health and safety of Santa Clara County residents under the guise of cutting red tape,” said Santa Clara County Counsel Tony LoPresti. “Our community is already facing the impacts of climate change—including devastating wildfires and deadly heatwaves. These science-based standards have saved lives and improved air quality for over a decade and rolling them back will deepen the risks to public health and our local economy, both now and for generations to come.”

Background
Under the federal Clean Air Act, EPA is required to regulate pollutants from vehicles that cause or contribute to dangerous air pollution. The U.S. Supreme Court’s 2007 decision in Massachusetts v. EPA confirmed that greenhouse gases are an air pollutant under the Clean Air Act. Following that opinion and years of thorough scientific research, EPA acknowledged in 2009 that greenhouse gas emissions from motor vehicles contribute to air pollution that harms public health and welfare in numerous ways. The agency then set standards to limit motor vehicle greenhouse gas emissions.

In 2025, EPA proposed to eliminate the Endangerment Finding based on a dubious, updated review of climate science and a draft report the Department of Energy’s defunct “Climate Working Group.” The working group was disbanded in the face of legal challenges and never issued a final report. The draft report, circulated last July and cited in EPA’s proposal to roll back the finding, drew significant criticism from scientists. Despite the legal challenges and intense scrutiny from the scientific community, EPA repealed the Endangerment Finding last month and eliminated all existing and future federal greenhouse gas standards for vehicles.

The recission of the finding will upend regulatory processes that have been in place for 15 years. Pollution from the transportation sector will skyrocket. American investment in clean technologies and jobs will slow, undermining U.S. leadership in both transportation and climate action.

The lawsuit alleges EPA’s rescission of the Endangerment Finding violates the Clean Air Act and the Administrative Procedure Act. EPA is relying on the faulty argument that it lacks the authority to regulate greenhouse gas emissions—an argument previously rejected by the U.S. Supreme Court. Plaintiffs argue EPA is disregarding the extensive scientific evidence that greenhouse gas emissions endanger public health and welfare, and eliminating all existing and future greenhouse gas emission vehicle standards violates EPA’s legal duty to protect the public from environmental harm. Plaintiffs are asking the Court to vacate EPA’s illegal rescission of the Endangerment Finding and restore EPA’s greenhouse gas emission standards for vehicles.

San Francisco and Santa Clara County join 25 attorneys general, the Governor of Pennsylvania, and ten cities and counties in the lawsuit. The effort is led by the attorneys general of Massachusetts, California, New York and Connecticut.

The case is Commonwealth of Massachusetts, et al. v. United States Environmental Protection Agency, et al., United States Court of Appeals for the District of Columbia Circuit. View a copy of the petition.