When the director Davis Guggenheim was completing the documentary “An Inconvenient Truth,” his team had an idea: Let’s get a famous singer to write a song to end the movie. Al Gore, the film’s centerpiece, suggested Melissa Etheridge.

Mr. Guggenheim drove to her house in the San Fernando Valley and watched the film with her on a TV, he recalled. “At the end, she said — in a very kind way — ‘You should leave now. I need to write a song.’”

That song, “I Need to Wake Up,” was crowned best original song at the 2007 Academy Awards. (The movie won best documentary feature.) Since then, no song from a documentary has won the prize. But it’s not for a lack of trying.