Earlier this month, US President Donald Trump’s administration drew a flurry of condemnations for its decision to repeal the Environmental Protection Agency’s “endangerment finding”: a formal, evidence-based acknowledgement that greenhouse-gas emissions pose a threat to public health. Although the change may seem minor, it is anything but. Since 2009, the endangerment finding has underpinned much of the climate-related policymaking at the EPA and other agencies.