Which celebrity narrates a new Climate change ad?

Billionaire Tom Steyer has already spent millions to make climate change a campaign issue this year. Now his super PAC, called NextGen Climate Action Committee, is employing some star power to raise awareness of the issue.

The super PAC's latest ad was directed by Darren Aronofsky, who's known for directing films like Black Swan and Requiem for a Dream. The ad is narrated by Woody Harrelson, though the actor doesn't appear in the 30-second spot.

"They told us the world was flat and insisted it was the center of the universe," Harrelson says over vintage-looking black-and-white images. "They ignored pollution, said that cigarettes were harmless, that leaded gas was safe, and there was nothing wrong with CFCs."

There's no indication of who "they" are, but the ad then switches to modern-day footage of natural disasters and a shot of billionaire conservative David Koch, one of the leaders of the energy and manufacturing conglomerate Koch Industries.

"Now they tell us climate change is a hoax," Harrelson says. "Some powerful people want to hold us back."

The ad doesn't mention any specific candidates or political parties, though it is running this week in the key states of Florida, Colorado, Michigan and Iowa. It will air during the World Series and prime time, NextGen confirmed to CBS.

NextGen Climate has so far spent more than $50 million this election cycle, the group confirmed to CBS, to make climate change a wedge issue.

A recent Gallup poll showed that climate change is a low priority for voters. In a Sept. 25-30 poll, registered voters were asked to rate the importance of 13 issues. Just 40 percent said climate change was extremely or very important, putting it dead last.