Updated September 26, 2025

The U.S. Department of Justice filed an amicus brief earlier this month urging the Supreme Court to take up the Boulder, Colorado climate lawsuit. In its filing on September 11, the DOJ called the Colorado Supreme Court’s decision allowing the case to proceed “manifestly wrong,” warning that the county’s claims are both unconstitutional and should be preempted by federal law.  

The Trump DOJ’s brief argues that if the US Supreme Court lets the Colorado Supreme Court decision hold, “then every locality in the country could sue essentially anyone in the world for contributing to global climate change.”  

That warning has now been reinforced by a coalition of 26 state attorneys general, led by Alabama, who filed a new amicus brief with the Supreme Court on September 26th. The states argue Boulder’s lawsuit is an unconstitutional power grab, effectively a “billion-dollar carbon tax” that would let one locality dictate national climate and energy policy. The filing argues only federal law can govern interstate or global emissions, warning that Boulder’s theory would lead to regulatory “chaos” as dozens of state courts attempt to set conflicting climate rules.

The brief calls the Boulder case a “perfect vehicle” for the Supreme Court to review, because the Boulder case more directly presents the constitutional question of whether states can regulate interstate emissions. The coalition of AGs also call out the potential implications for other industries like agriculture and food producers, citing New York’s now-dismissed lawsuit against JBS and ongoing Tyson litigation.

These strong requests give the Supreme Court a fresh opportunity to weigh in and potentially resolve growing discrepancies among lower courts on whether state-law claims over global climate change can move forward. 

DOJ Supports Defendants’ Warnings 

As EID Climate had previously noted, the defendants in the Boulder case petitioned the Supreme Court in August to review the Colorado court’s ruling.  

In their petition, the defendants cautioned that allowing Boulder’s suit to proceed under state tort law perpetuates an unsustainable and chaotic patchwork of climate regulation, and ultimately, threatens energy security across the United States.  

Those concerns are now reinforced by the U.S. DOJ amicus brief. The DOJ argues that Boulder’s case, which seeks local damages for the effects of global climate change, involves uniquely federal interests and should not be decided under a patchwork of state laws:  

“If, as the Colorado Supreme Court held, those theories are consistent with federal law, then every locality in the country could sue essentially anyone in the world for contributing to global climate change.” 

Legal scholars and well-known academics Richard Epstein and John Yoo made the same point in their own amicus brief, stressing that Boulder’s theories collapse under and basic tort principles, and that the county cannot set national climate policy: 

“In every tort case, a plaintiff must show that the actions attributed to the defendant has caused the specified harm. But here, the complaint does not do that.” […]

“The increasing demand for Respondents’ products in Colorado and worldwide has a far greater impact on consumption than anything Respondents supposedly said.” […]

“Neither Boulder, Colorado, nor other state and local actors applying state and local common law and statutes can decide climate and energy policy for the entire Nation.” 

Several additional amici echoed similar warnings. The American Tort Reform Association pointed out that:  

“Claims alleging property damage or financial losses from changes in global weather patterns are not traditional matters of state tort law. These lawsuits attempt to set national public policy and environmental regulation through state law claims – regulation through litigation.” 

Similarly, legal experts the Washington Legal Foundation also raised the alarm on this issue in a separate amicus filing supporting the defendants:  

“Allowing state courts to regulate global climate change through tort suits threatens national economic stability and federal authority.” 

SCOTUS Request to Boulder Suggests Interest  

Notably, Boulder initially waived their right to respond to the companies’ petition, suggesting that Boulder was confident the petition would be denied without the need for their input.  

However, the Supreme Court did not let Boulder off the hook, and requested a formal response by October 9, after which the justices will convene to decide whether to take up the case this term.  

Wave of Dismissals Underscores Legal Challenges 

The Boulder lawsuit is one of a handful of climate damage cases that have advanced past preliminary motions, and it now stands in stark contrast to a broader trend of dismissals.  

Courts in New York, Delaware, Maryland, and other states have all dismissed similar climate lawfare cases in recent months.  

Against this backdrop of failures, Boulder’s case stands as an outlier. In May, the Colorado Supreme Court, in a 5–2 decision, rejected the energy producers’ defense and allowed Boulder’s claims to proceed under state law. However, the two Colorado justices in dissent issued a clear warning that Boulder’s lawsuit reaches far beyond local affairs. As Justice Carlos Samour stated:  

“Boulder is not its own republic; it is part of Colorado and, by extension, of the United States of America. Consequently, while it has every right to be environmentally conscious, it has absolutely no right to file claims that will both effectively regulate interstate air pollution and have more than an incidental effect on foreign affairs.”  

Bottom Line: While judges in New York, Delaware and Maryland have thrown out nearly identical climate lawsuits, Colorado allowed Boulder’s case to proceed, creating a clear conflict. With the DOJ and 26 states warning of ensuing chaos from a patchwork of state-level climate tort rules, the stakes could not be higher.  

Should the Supreme Court take up Boulder’s case, the justices have an opportunity to finally put an end to frivolous climate lawfare. Global climate change is fundamentally a political question for elected representatives and voters, not for the local courthouse.