'Years of Living Dangerously' producers Joel Bach and David Gelber tell THR how they nabbed the star for the Emmy-winning series' second season.

David Letterman is heading back to TV, but he's leaving the desk behind.

The longtime late-night TV personality will appear on the second season of the Emmy-winning documentary series Years of Living Dangerously, which centers on the issue of climate change. This marks Letterman's first TV project since signing off as host of CBS' Late Show in May.

Producers Joel Bach and David Gelber talked to The Hollywood Reporter about how Letterman came on board, explaining that they decided to reach out to him after seeing his passion for the issue when he interviewed scientists on the Late Show.

"It's thrilling to have him do this — we're beyond excited," Bach says. "The reason why Letterman's part of this is that we just noticed that he seemed to perk up when this issue came across his lap. We reached out to him to see if he'd want to be part of this, and he said, 'Absolutely.' He said [that climate change is] something he does think about a lot."

Letterman will appear on one of the new season's eight episodes, as he'll head to India to speak with Prime Minister Narendra Modi about the nation's energy concerns.

"He's never been to India, and he's really excited to go," Gelber says of Letterman. "Dave will be a terrific correspondent for us. We're very comfortable having him with the Prime Minister of India — I'm not sure there are that many people we'd be comfortable setting up in that kind of role. He's a wonderful interviewer."

The series' new season will premiere on the National Geographic Channel, after its first season aired on Showtime. Other guests set for season two include Ty Burrell, James Cameron, Don Cheadle, Arnold Schwarzenegger, Olivia Munn, Ian Somerhalder and Cecily Strong. Burrell's episode will focus on electric cars, while Schwarzenegger will be visiting China.

Jack Black will also appear this season, and his episode came about after Jerry Weintraub — who was an executive producer on the series and was close with Black — died in July.

"Jack understood that Years of Living Dangerously was important to [Weintraub]," Gelber said. "Right after Jerry died, Jack agreed that he would be part of it, in part as a tribute to Jerry and in part because he really believes in the story."

National Geographic Channels CEO Courteney Monroe tells THR that the series has "found its rightful home on the network." She points out that Letterman's involvement "speaks to how passionate so many people are — like himself — about this issue and how important it is to our planet and to humankind, and I think it's terrific that he's attaching himself to it."

Monroe adds: "What's interesting and important is this is not a political issue at all, but it's an incredibly important issue that affects all of us as people living on this planet, and I think that's why they're able to attract the names that they've attracted."

Years of Living Dangerously's second season is set to premiere on the National Geographic Channel in the fall of 2016.

Email: Ryan.Gajewski@THR.com

Twitter: @_RyanGajewski