(L to R) Richard Cizik and Eric Chivian.
AGE: 66 and 57, respectively
PREVIOUS APPEARANCES ON THE TIME 100: 1
PRO: Chivian is a professor of psychiatry at Harvard, while Cizik is one of the world's foremost Evangelicals. Despite their seemingly contradictory dogmas, the two men have united theologians and scientists in a common cause: protecting the earth.
CON: This winter, Cizik was forced to resign from the National Association of Evangelicals after making statements in favor of same-sex unions. Will the uproar distract from his environmental work?