The Trump administration’s decision to repeal a major scientific finding that lets the government regulate vehicle pollution drew sharp criticism from Colorado officials and environmental groups, who said it will raise prices and lead to a slew of health impacts. 

In 2009, the Environmental Protection Agency found that planet-warming greenhouse gases — like methane and carbon dioxide — could harm human health. That cleared the way for a host of pollution limits on everything from tail pipes to power plants. 

But the EPA repealed the finding last week, which means it can no longer set limits on emissions from cars and trucks. Vehicle emissions are the largest source of pollution in Colorado, and contribute to frequent smoggy days along the Front Range. 

Will Toor, head of Colorado’s Energy Office, said that repealing the finding would lead manufacturers to sell dirtier, less efficient cars starting in a few years. He added that Colorado would push ahead with its ambitious climate targets despite the federal government. 

“They’re definitely making life more expensive and making the air dirtier,” Toor said. “But I think they’re only marginally able to slow progress.”

Governor Jared Polis also blasted the repeal and said that increased pollution would hurt children, seniors and Coloradans with health conditions. 

Cyrus Western, the Trump administration political appointee who oversees EPA’s Region 8, which includes Colorado, sharply disagreed with those interpretations. He said repealing the finding would not harm air quality — and might actually improve it. He also said the EPA would continue to zealously go after polluters. 

“Some people are saying that repealing the endangerment finding is a signal to polluters that they can just pollute left and right,” he said. “And that is fundamentally not true at all.”

Even so, there may be workforce challenges to actually regulating polluters. Since November 2024, the EPA has lost roughly 2,000 employees — nearly 12% of its staff – through layoffs and resignations. 

The repeal has already triggered at least one lawsuit to force the EPA to change course, with more cases likely on the way. 

A brewing legal battle likely headed to the high court

It’s likely that any lawsuits challenging the repeal would end up at the Supreme Court, which may limit or overturn its own decision about greenhouse gases. 

In 2007, the Supreme Court issued a major environmental ruling, which said the EPA had the authority to treat greenhouse gases as pollutants, and regulate them under the Clean Air Act. 

That law does not explicitly mention greenhouse gases as pollution. But Chris Winter, executive director of the Getches-Wilkinson Center at CU Boulder’s Law School, said the ruling made it clear that the Clean Air Act was written with a “sweeping definition” of pollution, which could include planet-warming gases. 

The EPA’s announcement, on the other hand, takes a much narrower approach to regulating and limiting greenhouse gases. Western said that the endangerment finding was “bad policymaking,” because it was written by the agency and not by elected officials in Congress. 

“The agency never had permission by Congress or a requirement by Congress to regulate greenhouse gases,” he said. “The agency basically just made it up out of [thin] air.”

But the finding, and hundreds of pages of supplemental reports, summarize numerous scientific studies to conclude that the pollutants driving climate change also threaten human health. 

Since then, a large body of work has only strengthened the scientific consensus around the health and economic effects of climate change — from wildfire smoke inhalation to extreme heat waves. 

Western said that even with the repeal, “the Clean Air Act is still the supreme law of the land,” and that the EPA could use other tools, like state-level ozone plans, to limit emissions from  transportation. 

But the repeal sets the stage for the Trump administration to begin rolling back limits on other polluting sources, like power plants and oil and gas wells, according to Winter.   

Repealing the finding “flies directly in the face of…binding Supreme Court precedent,” Winter said. 

The cost of pollution

President Trump and EPA administrator Lee Zeldin have frequently dismissed and denigrated climate science. They, along with Western, said that repealing the finding would save consumers and automakers money.

“I think it’s indisputable that in the long run that this is going to actually save the consumers huge sums of money,” Western said, who added that the agency is still committed to fuel-efficient engines. 

Environmental groups and state officials strongly disagree, and say that less efficient cars would lead to higher costs. 

An analysis by the Environmental Defense Fund, which is suing the Trump administration over the repeal, found that Coloradans would be saddled by more than $19 billion in additional gasoline costs through 2055. 

A separate analysis by the American Council for an Energy-Efficient Economy found that less efficient cars would eventually cost drivers thousands of dollars in additional fuel and maintenance costs over the lifetime of their vehicles.

Western said it was clear that the EPA could still regulate greenhouse gases, but only if it received explicit congressional authority. 

“The endangerment finding was a deviation from that process, and caused a lot of damage,” he said. 

But Winter said that the costs of not regulating pollution would be enormous, as climate change contributes to extreme weather, including historically low snowpack across the West, and impacts water supplies, agriculture yields and the frequency of damaging wildfires. 

“There’s a whole other set of cascading effects from climate change that the Trump administration doesn’t want to talk about, but has very real economic implications for people in Colorado,” he said.