An Inconvenient Truth
Did Al Gore—with those cartoons of Mr. Sunbeam and greenhouse-gas goblins—oversimplify the facts? Were the projections showing Manhattan underwater too dire? Did he turn himself into a lightning rod for skeptics? Perhaps. But Davis Guggenheim's 2006 film on Gore's nationwide campaign to sound the climate-change alarm works because of Gore's lecturing style: patient, accessible, and scarily informed. The film permanently elevated the national discourse on the most crucial issue of our time.

Who Killed the Electric Car?
While Martin Sheen's narration is occasionally wooden, this 2006 murder mystery is otherwise pitch perfect. The victim here is the General Motors EV-1, a concept car that was released to California drivers in 1996 in response to the state's 1990 Zero Emissions Vehicle Mandate, only to be literally thrown on a scrap heap in 2003. Director Chris Paine finds plenty of Big Oil and Big Auto villains, but he lays equal blame on us consumers, and avoids turning his film into an anticapitalist screed. Who Killed demonstrates that we had the technology to usher in the era of the smart car long before Toyota did, and long before Detroit had to beg for a bailout.

Food, Inc.
Super Size Me, Morgan Spurlock's 2004 McDonald's binge, was more popular, but Food, Inc. stands as the signal culinary documentary of our time. With images like headless chickens shuttling down factory lines, the Robert Kenner–directed film offers a quick and very dirty crash course in subjects we knew we were wary of—Uncle Sam's subsidization of the corn industry; feedlots; E. coli; genetically modified crops—but until now had never seen in such graphic terms.

Gasland
An exposé on clean natural gas's dirty secrets? We don't hear you stampeding to theaters. But Josh Fox's new film is a fresh successor to investigative docs like Food, Inc. Fox is Michael Moore without the ranting: Approached by energy companies hoping to drill on his Pennsylvania land, he sets out on a cross-country road trip to explore the side effects of drilling. Everywhere he goes, he finds Americans reporting illnesses and some of the mankiest-looking water this side of Bangalore. With natural gas touted as the savior to our energy woes, this film is one you won't want to miss. And wait'll you see the pyrotechnics. Many characters in this movie can—and will!—set their water on fire.

The Cove
Night-vision goggles, bad guys wielding harpoons, corrupt cops, hidden cameras—never has environmentalism seemed this exciting. This exposé of the now infamous dolphin slaughter in Taiji, Japan, plays like a thriller, right up to the denouement—activist Ric O'Barry walking into an International Whaling Commission meeting with footage of the hunt playing on a video monitor strapped to his chest. The Cove won the 2010 Oscar for Best Documentary, and established director Louie Psihoyos as the anti–Paul Watson, a guy who spurs change with his camera, not his antics.