John Holdren, the director of the White House Office of Science and Technology, took on climate change skeptics Wednesday in a video released on YouTube saying the cold weather that swept across the United States this week doesn’t mean that global warming is a myth.

“If you’ve been hearing that extreme cold spells like the one we’re having in the United States now disprove global warming, don’t believe it,” Holdren says in the video. “The fact is that no single weather episode can either prove or disprove global climate change.”