In 2004, Arizona senator McCain famously called the Bush administration's lack of climate-change policy "disgraceful." Today, as one of the few Republican candidates backing mandatory caps on greenhouse-gas emissions, he vows to make global warming a key issue if elected.

Battle Cry: "We can address global-warming issues through free-enterprise-system-driven green technologies. GE dedicated itself to green technologies, and guess what: They're still making a lot of money."

Green Chops: McCain partnered with Democratic senator Joe Lieberman to sponsor the 2003 Climate Stewardship Act, the first Senate bill to call for mandatory greenhouse-gas limits. Since 2004, he's visited Greenland, Iceland, Norway, and Alaska, which he calls "the miners' canaries, visible manifestations of the tremendous harm that global warming has done." McCain is the only GOP candidate actively opposed to drilling in ANWR.

Power Points: He would end subsidies for fossil-fuel industries and let the markets work in favor of renewable energy.

Outside Moment: "Last year, my son Jack and I hiked the Grand Canyon, rim to rim. It wasn't the first time."

Eco-Hero: Morris and Stewart Udall, former Arizona congressmen (and Dems). "Mo, who was incredibly effective at getting environmental protections through Congress, and his brother Stew, who was U.S. secretary of the interior for eight years, were two of the great environmentalists of the 20th century."

Hmmm: If elected, he's said he'll repeal the Roadless Area Conservation Rule, which bans logging and new-road construction on 58.5 million acres of national forest and grasslands.