California Gov. Jerry Brown (D.) compared President Donald Trump supporters to ignorant cave dwellers at a climate change event Monday in New York City.

“They’re both kind of very similar. You should check out the derivation of ‘Trump-ite’ and ‘troglodyte,’ because they both refer to people who dwell in deep, dark caves,” Brown said in remarks reported by Politico.

The California governor, speaking at an event during Climate Week NYC, said the election of  Trump has made it easier to promote climate-related policies. Trump is a “real adversary that is not believable, is not credible,” according to Brown.

“President Trump is the null hypothesis, which he’s proven. Everything he’s doing is … stupid and dangerous and silly. I mean, come on, really, calling the North Korean dictator ‘Rocket Man?’ … He is accelerating the reversal through his own absurdity,” Brown said.