From his Wikipedia page:
Hartmann is considered to have progressive/liberal politics, although he describes himself as part of the radical middle...Leonardo DiCaprio made a web movie titled Before The Flood, inspired by The Last Hours of Ancient Sunlight. Hartmann appears in DiCaprio's 2007 documentary The 11th Hour, as well as the feature documentary film Dalai Lama Renaissance (with Harrison Ford), and Crude Impact. In 2010, Warner Brothers and Leonardo DiCaprio[36] announced they are making a motion picture based on the book Legacy of Secrecy, authored by Lamar Waldron and Hartmann.