OK, so the green movement needs to get away from the words “environment,” “Earth,” and “planet,” but TV host Bill Maher has a fantastic point (for once): If you care about sustainability — hell, if you care about the future at all — you should be seriously worried about overpopulation.

Maher spoke with Countdown author Alan Weisman in an insightful, much-needed conversation. “This is a topic most environmental groups won’t touch,” Weisman began. (We will!)

Weisman noted that Iran has the best family planning programs in history, with free birth control and premarital classes that teach just how frickin’ expensive it is to raise a kid. Plus, women are encouraged to stay in school, which delays parenthood. (As Maher says, “Education is the best contraception.”) Watch — it’s eight minutes worth seeing:

Maher also drops the sobering fact that Americans comprise 5 percent of the global population but use about 20 percent of its resources. Driving a Prius and using solar is awesome, but to really make a difference, put a jimmy hat on it.

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