The Trump administration on Thursday revoked a scientific finding that long has been the central basis for U.S. action to regulate greenhouse gas emissions and fight climate change, the most aggressive move by the Republican president to roll back climate regulations.

The rule finalized by the Environmental Protection Agency rescinds a 2009 government declaration known as the endangerment finding that determined that carbon dioxide and other greenhouse gases threaten public health and welfare. The Obama-era finding is the legal underpinning of nearly all climate regulations under the Clean Air Act for motor vehicles, power plants and other pollution sources that are heating the planet.

The repeal eliminates all greenhouse gas emissions standards for cars and trucks and could unleash a broader undoing of climate regulations on stationary sources such as power plants and oil and gas facilities, experts say. Legal challenges are near certain.