IF IT WEREN'T FOR GLOBAL WARMING, Steger, a self-described "closet introvert," might still be living "a beautiful, simple life" at the Homestead, his 240-acre, 100 percent solar-, wind-, and propane-powered compound near Ely, Minnesota.

But that life is on hold, as is Steger's once-firm plan to retire from expeditioning. I visited him at the Homestead last November, prior to the L.A. trip. On a suspiciously balmy Minnesota afternoon, during a tour of a half-dozen Homestead buildings where Steger designs and builds equipment for his many adventures, he told me that, after three decades of traveling over polar ice, he's found his true calling: to make the world confront the reality of climate change.

The reality, as Steger sees it, is clear. The heat is on, thanks largely to the rapid release of carbon dioxide brought on by mankind's burning of fossil fuels. Today, CO2 levels are the highest they've been in at least 650,000 years, with effects that are most obvious in the polar regions. Two major ice shelves, the Arctic's Ward Hunt and Antarctica's Larsen, have broken up in the past 20 years, while Arctic sea ice has lost a third of its thickness and more than a quarter of its extent.

Steger, who's seen the changes unfold firsthand, has been infatuated with climatology, meteorology, and biology since he was eight. To him, the situation makes it impossible not to do something.

"Once you see what's happening as a moral issue, the mass extinction and other implications of what we've done and what's going to happen," Steger says, "you lose a certain purity of peace that forces you into action."

This from a man whose mind and body are in perpetual motion. At 15, Will and his older brother, Tom, launched a powerboat journey from Minneapolis down—and back up—the Mississippi River, occasionally landing in jail and getting sprung only after their parents assured the police that they hadn't stolen the boat. When Steger was 17, he and a buddy hitchhiked to Juneau, Alaska, where they paddled across blank, unmapped territory in the Yukon and Alaska.

Between adventures, Steger worked odd jobs to pay his way through Catholic high school, college, and graduate school. In 1970, he hitched to Colorado, where he was hired on the spot as an Outward Bound instructor. Two years later he moved to California, where he spent time at a Zen monastery, followed by weeks of trekking and fasting in the Sierras. In 1974 he returned to Minnesota, where he leased a team of sled dogs and started an outdoor-education school at his property near Ely.

"Everyone thought I was nuts," says Steger, referring to the locals, a stoic Slavic bunch who earned a hard living out of timber and mining. "I didn't know anything about sled dogs."

He learned, and in 1982 he launched an 18-month, 7,200-mile dogsled expedition in the Canadian Arctic and Alaska, which inspired him to try another polar trek—all the way to the North Pole. The aim was to do it the hard way, taking everything his eight-person team needed and nothing more.

"The North Pole was do or die," Steger says. "I was not coming back unless I made it." In 1986, Steger's team became the first to dogsled to the top of the world without resupply.

"Will is an absolute genius at expedition logistics," says Paul Schurke, the co-leader of that famous trip. "We left the north shore of Canada with 7,000 pounds of supplies, which Will tracked meticulously. We arrived at the Pole with eight pounds left."

Steger parlayed his skill into other firsts: In 1988, he completed a 1,600-mile south-north traverse of Greenland, the longest unsupported dogsled expedition in history. In 1989–90, he led the International Trans-Antarctica Expedition, a 3,741-mile dogsled traverse of Antarctica, a massive $2.5 million undertaking.

"The first North Pole trip was like a sporting event," Steger says. "But the purpose of Antarctica was to make the continent famous, so that world leaders would protect it from mineral exploration."

For more than seven months, Steger and five teammates battled windchills of minus 150 degrees and mind-numbing whiteouts. After they finally succeeded, the exuberant multinational team traveled the globe, lobbying leaders to forbid mineral extraction in Antarctica. In 1991, the Protocol to the Antarctic Treaty was adopted, banning mineral and oil exploration on the continent for another 50 years.

After a fourth major expedition—a successful traverse from Russia to Ellesmere Island in 1995—Steger's luck ran out. In 1997, just seven days into a solo attempt to haul and paddle from the North Pole to Ellesmere Island, he aborted.

"I was dropped off at the Pole by a Russian icebreaker and got into horrible conditions," Steger told me as he stoked a fire inside his compact bachelor cabin, which is packed with books on architecture and exploration. "I made one final try and, for some reason, I just said, No más. I had to organize a rescue."

And that was it.

"I left expeditioning," Steger said. "The demands of marketing and the media were too complicated. I was so stressed that I came back here. It was quite a relief."