David Letterman's post-retirement plans revealed

David Letterman was tight-lipped about his future plans when he signed off from "The Late Show" four months ago, but we will see him next year in a rather unlikely place, CBS News' Carter Evans reports.

"I doubt that anybody will ever see me again," Letterman had said in an interview with "Sunday Morning."

Letterman will be traveling to India to appear in an episode of "Years of Living Dangerously," a documentary series on the National Geographic Channel focusing on climate change.

"The producers for the NatGeo docuseries actually said that any time a climate change story came across his desk on Letterman's show that he was so passionate about it ... They reached out to him and said, 'Hey, would you be interested in doing this?' And he was, he jumped right at it," Variety TV reporter Elizabeth Wagmeister said.

Letterman has never been shy about addressing environmental issues on "The Late Show," and environmentalists were often guests, including Bill McKibben.

You might expect this kind of post-late-night activism from Jon Stewart, now speaking out on behalf of 9/11 first responders, or by some of the other stars seen on "Years of Living Dangerously," like Harrison Ford or Matt Damon.

"I think he will add a Letterman flair that will be really interesting to see him kind of with a more darker subject matter," Wagmeister said.