Liberal activist Steyer calls out Kochs in ad

Billionaire climate activist Tom Steyer is throwing down the gauntlet in a new ad targeting conservative billionaires Charles and David Koch over climate change.

The 15-second ad buy plays a short clip of stars in the night sky with crickets chirping in the background, and the statement, "The Koch brothers' response to a climate change debate with Tom Steyer" plastered across the screen.

NextGen Climate, founded by Steyer in 2013, is calling out the Koch brothers in the new ad for failing to respond to Steyer's invitation to debate U.S. energy policy, Keystone XL and climate change.

During an appearance on HBO's "Real Time with Bill Maher" last month, Steyer formally invited the conservative donors to a debate.

"More than three weeks later, the Koch brothers have chosen to remain in the shadows, and all we've heard is crickets," NextGen Climate said on Friday.

The new ad will air Sunday during NBC's "Meet the Press," ABC's "This Week," CBS's "Face the Nation" and "Fox News Sunday," in Washington, D.C., and Wichita, Kan.

Both Steyer and the Koch brothers have ramped up their campaign push in the past few months, offering fodder to lawmakers in both parties.

Democrats have railed against Republicans for bending to the will of the Koch brothers, who made their fortunes in the oil and gas industry.

Republicans are starting to do the same, accusing Democrats of pushing drastic climate policies in order to attract contributions from the liberal Steyer.