On Thursday, a coalition comprising two dozen states, alongside numerous cities and counties, launched a legal challenge against the Environmental Protection Agency (EPA). This lawsuit opposes the Trump administration’s decision to overturn a scientific determination that had been pivotal for U.S. measures to regulate greenhouse gas emissions and address climate change.

Last month, the EPA finalized a rule that nullified the 2009 endangerment finding. This finding had previously established that emissions of carbon dioxide and other greenhouse gases pose a threat to public health and welfare. Serving as the legal foundation for nearly all climate regulations under the Clean Air Act, this finding was crucial for controlling emissions from vehicles, power plants, and other major pollution sources contributing to global warming during the Obama administration.

The repeal effectively removes all greenhouse gas emissions standards for vehicles and could potentially lead to a widespread rollback of climate regulations affecting stationary sources, including power plants and oil and gas facilities.

The lawsuit, submitted to the U.S. Court of Appeals for the District of Columbia Circuit, marks the second significant challenge to the endangerment finding’s repeal. It follows a previous suit filed by public health and environmental advocacy groups last month.

This legal action argues that the EPA’s decision to rescind the endangerment finding neglects its fundamental duty to protect the American public.

“Rather than assisting Americans in confronting our new climate reality, the Trump administration has chosen a path of denial, dismantling essential protections that are critical to the federal response to climate change,” stated New York Attorney General Letitia James. She spearheaded the lawsuit with the attorneys general from Massachusetts, California, and Connecticut.

In all, 24 states, 10 cities and five counties joined the lawsuit. All are led by Democrats.

“Climate change is real, and it’s already affecting our residents and our economy,” said Massachusetts Attorney General Joy Campbell. “When the federal government abandons the law and the science, everyday people suffer the consequences.”

Massachusetts “has long led the way in protecting our communities from the dangers of greenhouse gas emissions and we are proud to stand up once again to lead this fight for our future,” she said.

The U.S. Supreme Court, in a landmark 2007 case, ruled that carbon dioxide and other greenhouse gases are “air pollutants” under the Clean Air Act. Since the high court’s decision, in a case known as Massachusetts v. EPA, courts have uniformly rejected legal challenges to the endangerment finding, including a 2023 decision by the D.C. appeals court.

EPA spokeswoman Brigit Hirsch said the latest lawsuit was “not about the law or the merits of any argument.” Instead, the plaintiffs “are clearly motivated by politics,” she said.

The EPA “carefully considered and reevaluated the legal foundation” of the 2009 finding in light of recent court decisions, including a 2022 Supreme Court ruling that limited how the clean air law can be used to reduce carbon dioxide emissions from power plants, Hirsch said.

In addition to New York, Massachusetts, California, and Connecticut, the case was joined by attorneys general of Arizona, Colorado, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New Mexico, Nevada, North Carolina, Oregon, Rhode Island, Vermont, Virginia, Washington and Wisconsin, as well as the District of Columbia and U.S. Virgin Islands.

The Pennsylvania Department of Environmental Protection also joined the case, along with the cities of Albuquerque, Boston, Chicago, Cleveland, Columbus, Denver, Los Angeles, New York and San Francisco, and five counties in California, Colorado, Texas and Washington state.

The dispute is likely to end up back before the Supreme Court, which is now far more conservative than it was in 2007.