18 months after leaving CBS's Late Show, David Letterman will make a rare television appearance. The 69 year old, will be a correspondent for an episode of the National Geographic Channel's docu-series, "Years of Living Dangerously."

Letterman won't be telling jokes on his appearance. Instead he'll visit with the Prime Minister of India, Narendra Modi, on how one of the world's largest populations is moving from non-renewable energy to solar power.

The subject matter of the Emmy Award winning series, covers environmental issues and climate change, things that are near and dear to the comedian's heart.

Look for stars Arnold Schwarzeneggar, Don Cheadle, and America Ferrera along with Letterman when the show premiers it's 2nd season, October 30th.