Attorney General Mayes Challenges Unlawful Rescission of Landmark 2009 Greenhouse Gas Endangerment Finding

PHOENIX— Attorney General Kris Mayes today joined a coalition of states, counties and cities to challenge the U.S. Environmental Protection Agency’s unlawful attempt to rescind its 2009 Endangerment Finding – the agency’s seminal determination that greenhouse gas pollution from motor vehicles drives climate change and endangers public health and welfare.

“On the day we file this lawsuit, much of Arizona is under an extreme heat warning due to an unprecedented early heatwave that has spiked temperatures over twenty degrees above normal,” said Attorney General Mayes. “The science behind the 2009 Endangerment Finding is real and grounded in rigorous research. It is abundantly clear that greenhouse gas pollution has fueled climate change in our state and across the entire planet. The decision by the Trump administration to rescind the Endangerment Finding will only accelerate climate change. Putting the profits of the fossil fuel industry over the future of our planet is a failure of historic proportions and we will fight it with every tool we have.”

The 2009 Endangerment Finding was the direct result of the landmark 2007 Supreme Court decision in Massachusetts v. EPA, which confirmed that the Clean Air Act authorizes EPA to regulate greenhouse gas emissions that endanger public health and welfare. Based on years of rigorous scientific analysis and review, in 2009 EPA determined that emissions from motor vehicles contribute to air pollution that harms public health and the environment.  EPA then set federal standards to limit those emissions, which have led to significant reductions in greenhouse gas emissions from motor vehicles. 

Now, almost two decades later, EPA has rushed a rulemaking process to rescind the Endangerment Finding and repeal all motor vehicles greenhouse gas standards, blatantly disregarding the law and science. EPA’s rescission is based on flawed interpretations of the law --- previously rejected by the Supreme Court — that the agency lacks authority to regulate greenhouse gas emissions. The rescission also ignores decades of peer-reviewed scientific evidence confirming the reality and severity of climate change. By eliminating all existing and future federal vehicle greenhouse gas emission standards, the rule violates EPA’s legal obligations, fundamental principles of administrative law, and its mission to protect public health and welfare. 

The threat of severe climate change in Arizona cannot be overstated.  In 2023, for example, Arizona experienced its hottest summer since recordkeeping began more than 100 years ago. In Maricopa County alone, more than 500 people died, and emergency rooms statewide recorded more than 4,000 heat-related visits.  The severity and frequency of high temperatures continues to increase, which poses risks to public health, infrastructure, and our economy.   

Climate change also increases the frequency and severity of wildfires, a constant source of danger in Arizona’s desert climate. Just last year, the Dragon Bravo Fire—one of the largest in Arizona history—burned 145,504 acres and destroyed 113 structures on the North Rim of Grand Canyon National Park, including the historic Grand Canyon Lodge.  Severe wildfires threaten human life, cause substantial landscape disturbance, and create significant and cascading economic impacts for the State and its residents.   

Today’s lawsuit is the latest action taken by AG Mayes and the coalition in their ongoing effort to fight back against EPA’s unlawful rescission of the 2009 Endangerment Finding.  In the fall of 2025, 23 attorneys general and seven counties and cities in submitting two comment letters urging EPA to abandon the proposal, arguing that it would violate settled law, clear Supreme Court precedent, and scientific consensus, endanger hundreds of millions of Americans—particularly communities disproportionately burdened by environmental harms—and cause unprecedented disruption to the regulatory landscape with catastrophic consequences for residents, industries, natural resources, and public investments.   

Co-led by the attorneys general of California, Connecticut, New York and Massachusetts, AG Mayes is joined in filing this challenge, by the attorneys general of:  Colorado, Delaware, Hawai‘i, Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New Mexico, Nevada, North Carolina, Oregon, Rhode Island, Vermont, Virginia, Washington, Wisconsin, the District of Columbia. In addition, this challenge is joined by Pennsylvania Governor Josh Shapiro; City of Boston, Massachusetts; City of Chicago, Illinois; City of Cleveland, Ohio; City of Columbus, Ohio; City and County of Denver, Colorado; City of Los Angeles, California; City of New York, New York, City and County of San Francisco, California; City and County of Santa Clara, California, and Harris County, Texas 
 
A copy of the filing is available.