The endangerment finding underpins the EPA's ability to regulate greenhouse gases. The Trump administration is trying to reverse it.

If approved, the EPA’s proposal would rescind the 2009 decision that set forth a legal basis to regulate greenhouse gases as pollutants. Known as the "endangerment finding," it allowed the EPA to limit emissions from vehicles, power plants, and oil and gas companies under the Clean Air Act.

In 2009, the Environmental Protection Agency declared that the rising concentrations of greenhouse gases in the atmosphere threatened public health and welfare. This “endangerment finding,” as it’s known in legal jargon,