Attorney General Phil Weiser testifies in opposition to EPA ending vehicle emission standards, climate protections

Aug. 20, 2025 (DENVER) – Attorney General Phil Weiser testified today before the U.S. Environmental Protection Agency in opposition to a Trump administration proposal, issued August 1, 2025, that would negate the EPA’s authority to regulate harmful air pollution from motor vehicles. The proposal would undo a landmark 2009 finding which held that vehicle exhaust contributes to climate change and endangers public health and welfare.

“The effects of climate change in Colorado are impossible to ignore, whether it’s increased drought or extreme wildfire danger, and we know it’s being driven largely by pollution from cars and other sources,” said Attorney General Phil Weiser. “Ignoring common sense, including scientific research from our own government, is a recipe for disaster. Eliminating requirements like vehicle emissions standards and refusing to acknowledge the reality of what is causing climate change puts at risk not only our physical health, but the health of Colorado’s economy. Climate change also exerts a disproportionate mental health burden on young people, in addition to its environmental impacts. The Trump administration is moving to undo the progress we’ve made and I’m going to keep doing everything in my power to stop it from doing so.”

The 2009 endangerment finding was the direct result of the landmark 2007 Supreme Court decision in Massachusetts v. EPA (PDF), which confirmed the EPA’s authority under the Clean Air Act to regulate greenhouse gas emissions that threaten public health and welfare. After years of scientific review, the EPA determined in 2009 that greenhouse gas emissions from motor vehicles contribute to air pollution that harms public health and welfare in numerous ways. The EPA’s new proposal seeks to reverse that finding with no grounding in law or science.

In his testimony, Attorney General Weiser told the EPA that the proposed rollback is contrary to established law, ignores decades of scientific evidence compiled by the agency under multiple presidential administrations, undermines the Clean Air Act’s model of cooperative federalism, and threatens to harm Colorado’s environment and economy.

The U.S. transportation sector is the leading source of greenhouse gas emissions in the country and is responsible for more than 3% of all global greenhouse gas emissions. Motor vehicle emissions contribute to the formation of smog, as well as fine particle pollution and toxic air pollution, all of which are linked to premature death, respiratory illness, cardiovascular problems, and cancer, among other serious health impacts.

The comment period for public input on the EPA’s proposal closes on September 22.

Read Attorney General Weiser’s testimony before the EPA (PDF).

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