President Donald Trump, accompanied by Environmental Protection Agency (EPA) Administrator Scott Pruitt, third from left, and Vice President Mike Pence, right, signs an Energy Independence Executive Order, Tuesday, March 28, 2017, at EPA headquarters in Washington. AP Photo/Pablo Martinez Monsivais There are many nonsensical assumptions made in President Trump’s new executive order, but one of the least defensible is the decision to calculate the “social cost of carbon” based on science from 2003.

The social cost of carbon puts a number on how much each ton of carbon dioxide emitted will cost us in the long run, thanks to its contribution to climate change.

It’s calculated based on a big-picture estimation of how damaging climate change will be overall.

This is obviously tough to estimate, but having even a ballpark number allows policymakers to have a rough way of comparing the potential future benefits of regulations to the small immediate savings.

Currently priced at $36 a ton, the social cost of carbon is mostly used for internal calculations, but since 2008, government agencies such as the Environmental Protection Agency, the Department of Energy, and the Department of Transportation have had to take it into account when making regulations.

Trump’s team has had its eye on this number for a while—in late January I wrote that while the existence of the number is mandated, how it’s calculated is flexible. Leaked memos had already shown that Trump’s people were targeting it, even though it technically wasn’t supposed to be recalculated until 2020.