The Ghost Park
Eighty percent of Yellowstone's signature whitebark pines are dead, like these, or close to it.
Credit: Christopher LaMarca
In the end, of course, there won't be a national day of mourning if or when the whitebark dies out. It's a commercially useless tree, too far up to interest loggers or summon camera-snapping tourists from Dallas. Furthermore, those forests won't remain bare long; at some point, firs and spruces will move up to replace them, chased higher by the ever-building heat. Much like the grizzly bears that its seeds support, whitebark registers as a low-end worry in an age of uppercase dread. Why would anyone underwater on his mortgage in Tucson expend a moment's thought on the matter?

Well, for starters, that house in Tucson (and Denver and San Diego) will be worthless when the spigots run dry. Among its unsung virtues, whitebark shelters the shrinking snowpack that feeds the water table in the West. Without the deep shade of its wide-armed canopy, the high snow would melt in torrents each spring, causing floods and mud slides in April and May and hellacious drought each summer. "In hydrology, when is as crucial as how much; you need slow, regular runoff that lasts you through August, when reservoirs are drained and farms need water," says Running. "An inch of snow is worth five of rain, because snow soaks deeper and evaporates slower. But with temperatures rising, we'll get less and less snow – to the point where it'll only stick in the high mountains."

Second, whitebark matters to the millions of people who fish the gin-clear waters of the Rockies. Early, heavy snowmelt makes for raging spring rapids – and streams too thin to fly-fish by mid-August. On a daylong boat float down the Yellowstone River with Skoglund and Laura Ziemer, an attorney who directs the Montana Water Project – an initiative of the nonprofit Trout Unlimited, which preserves and restores fisheries – I learned firsthand about the impact of warming on the region's signature species, the cutthroat trout. "We've seen massive fish-kills since the serious heat-up started a decade ago," said Ziemer. "As cold-water fish who've spent centuries here in 50- or 60-degree streams, the cuts can't adapt to late-summer waters that hit 80 degrees and higher." Rivers have been closed to anglers for weeks, trout populations have taken a staggering hit, and the thousands of outfitters who depend on fish "got kicked in the teeth," said Ziemer. Her organization has teamed with ranchers and Forest Service officials to offset some of the damage, resuscitating streams where cutthroats lay their eggs and modernizing water use on farms. But the changes in the environment are too systemic to be rolled back by grassroots groups alone. Says Craig Matthews, owner of the world-famous Blue Ribbon Flies, the go-to hook-and-bait shop in West Yellowstone: "We used to have 30 frost-free nights a year. Now it's 70, so the water gets hot and doesn't drop down after dark. Everywhere you look, these fish are pushed to the edge – and you can go right on up the line with other species."

One of those species is the grizzly. The park's bears used to fish for trout at the end of summer before heading up the hills to gorge on pine seeds. Now they're reduced to squirrels and berries and the occasional road-kill deer. A hundred years ago, there were roughly 50,000 bears living west of the Mississippi River. These days, there are maybe 1,500, and it's hard to imagine how Yellowstone's bruins will make it to the end of this century. So desperate have they become that they run toward gunfire, having learned that hunters leave gut piles after a kill. Their main chance may lie in one day quitting the park and heading north toward the Yukon Territory. There's a consensus building among wildlife groups to try to carve out a corridor to western Canada, in which bears, wolves, and lynx could come and go freely, roaming where there's food and cover. It's a plan fraught with peril – they'd have to cross three states, four superhighways, and two Canadian provinces – and opposed by a formidable cast of lobbies, primarily big ranchers and mining firms. But the winters there are arctic, the forests are robust, and the glacier-fed lakes teem with fighting trout and pike the size of beagles. We owe our bears nothing less than safe passage there, after trashing their habitat here. They'd better start now, though, to beat the rush. We'll all be heading north soon enough.