The “Late Show” host mocked the president’s insistence that his push for so-called “clean coal” would have no negative effect on the environment.

“I know clean coal sounds like an oxymoron, but so does President Trump,” Colbert said.

Tonight! Trump claims his rollback of Obama's environmental protections won't hurt the earth, but nature begs to differ. #LSSC pic.twitter.com/pDjjC1Jn8z — The Late Show (@colbertlateshow) March 29, 2017

To further highlight the absurdity of Trump’s claim, Colbert referenced his (fake) high school girlfriend who “worked with clean coal in the clean mines.”

“She told me that they mine the clean coal and put it on that silver-bullet train and then they sent it to Narnia where the Keebler Elves use it to power the pump on the fountain of youth,” Colbert said.

Check out the segment above.