"I was shocked. And happy at the exact same time because I really felt like it was an honor," he told AP Radio News on Thursday.
The Year of the Dolphin campaign is aimed at raising awareness of dolphins in the wild, the threats they face to their survival and actions that could help their wild conservation.
Carter, who starred on the E! Entertainment reality show "House of Carters" with his siblings, said he's still a student of the campaign.
"The issues involved with the dolphins are things that I am learning," the 27-year-old singer said. "I don't want to be this person to come across and say, `Why, I know what's going on' and shove it down people's throats. (Because) I don't know everything."
Carter said he will expand on the same feelings he expressed in a song he wrote called "Believe" in order to write a new anthem about the plight of dolphins.
"I am probably going to go back to the drawing board and try to outdo myself and write an even better song," Carter said.