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

This story is part of MIT Technology Review’s “America Undone” series, examining how the foundations of US success in science and innovation are currently under threat. You can read the rest here.

The mechanism that allows the US federal government to regulate climate change is on the chopping block.

On Tuesday, US Environmental Protection Agency administrator Lee Zeldin announced that the agency is taking aim at the endangerment finding, a 2009 rule that’s essentially the tentpole supporting federal greenhouse-gas regulations.

This might sound like an obscure legal situation, but it’s a really big deal for climate policy in the US. So buckle up, and let’s look at what this rule says now, what the proposed change looks like, and what it all means.