There was once a time when Rand Paul seemed like a moderate on climate change. A few months before he declared his candidacy for president, the Republican senator from Kentucky voted for an amendment stating that climate change is real and that humans contribute to it.

He was one of only 15 Republicans to do so. Paul also told Bill Maher last year that he’s not necessarily against regulating carbon dioxide, the main driver of human-caused global warming.

But all that moderation went down the tubes on Tuesday night during the fourth Republican presidential debate. Asked about President Obama’s regulatory plan to fight climate change, Paul said he would immediately repeal it — and then questioned the reality of the problem altogether.

“While I do think man may have a role in our climate, I think nature also has a role,” Paul said. “The planet’s 4.5 billion years old. We’ve been through geologic age after geologic age. We’ve had times when the temperature’s been warmer, we’ve had times when the temperature’s been colder. We’ve had times when the carbon in the atmosphere’s been higher.”

Here’s a video of Paul’s remarks, via The New Republic: