The Ghost Park
Eighty percent of Yellowstone's signature whitebark pines are dead, like these, or close to it.
Credit: Christopher LaMarca
The numbers come at you in a solid wall, wave after wave of peer-reviewed findings, each set worse than the last. The planet, heating steadily since the Industrial Revolution and growing warmer by leaps from 1980 onward, has suffered through 12 of the hottest years in history over the past 20. The decade just completed was the hottest on record, in which worldwide temperatures shot up a half degree. (For comparison, 1 degree was the total gain amassed during the entire 20th century.) The cause is well settled and the consensus broad; only a handful of crackpots and political opportunists deny that heat-trapping gases from fossil fuel burn-off are to blame for the bulk of the warming or insist that the spike is a statistical deviation brought on by cosmic rays and rogue currents.

The sharpest rebuke to the junk-science shills is the disaster now unfolding in the American West. States from the Dakotas on down to Nevada weathered devastating jumps of almost 2 degrees, or roughly double the rate of the planet's rise. The northern Rocky winters got radically milder, the summers started sooner and were drier and longer, and wildfires burned through vast tracts of timber weeks after the usual fire year ended. The damage to natural resources has outstripped the worst predictions of climate scientists everywhere: Lake Mead and Lake Powell, the largest reservoirs in the States and the lifeblood of Las Vegas and Los Angeles, respectively, stand half- empty and notching record lows, thanks to shrinking snowmelt. The country's greatest trout streams have been closed to anglers during parts of eight of the past 10 years, and the keystone trees of the interior West – the aspen, whitebark, and lodgepole pines – are dropping dead in holocaust numbers, felled directly by the surge of heat or by insect infestations spawned by it. And this is a mere prelude to the hellfire that's coming: a regional warming of as much as seven to 10 degrees by the end of this century, bringing permanent drought plains, coastal tsunamis, and widespread human dispersal. "Without a countershift the equal of the Industrial Revolution, we'll see mass migrations in our grandkids' lifetimes," says Steve Running, a renowned ecologist at the University of Montana and a lead author of the United Nations report on global warming in 2007. "Major cities in the West, like Phoenix and Las Vegas, may have to be abandoned as badlands."

Running is scarcely an outlier voice. "What we've seen out here is like nothing on record, and our tree-ring studies go back a thousand years," says Jonathan Overpeck, the co-director of the Institute of the Environment at the University of Arizona and one of the go-to climate scientists in the country. "The winters are shorter, the snowpacks melt early, and the drying seasons are longer and hotter, which leads to terrible wildfires and tree death. One of the many things that worry me, as the heat increases, is that this region becomes a second Outback. Already, our water supply is severely strained, and with decade-long droughts like the one we're in now, it's hard to see how we'll avoid it."

If the West is ground zero for the unholy experiment being conducted on weather shifts, then Yellowstone is first up on the blasting range. The oldest and most magical of our national parks, its 2 million acres stretch to three states, boast a spectacular chain of rivers, lakes, and creeks, and sit, a vast chunk of them, on a supervolcano that spawns half the world's geysers and hot springs. Among the last menageries of charismatic wildlife in the northern temperate zone, its grasslands feed herds of wapiti, moose, and bison, which in turn feed grizzlies, wolves, and mountain lions – a matchless array of sovereign predators. Four million people visit the park each year to fish its waters, run its trails, and climb its summits; to get anywhere near the top of the Gallatin Mountains and look down on those silver-backed buttes and falls is to know, in your bones, what beauty is. There is grandeur on all sides of you, but graveyards, too: mile after mile of zombified forests, dead from the roots but still standing.

One very warm week in early October, I took a four-day tour of Yellowstone's peaks and ravines with people who love the park dearly. My principal guide, an attorney named Matt Skoglund, was a rising star at a law firm in Chicago until he shucked it, in '08, to become a wildlife advocate, taking a job in Montana with the Natural Resources Defense Council at a fraction of his former wages. The NRDC, along with partner nonprofits like Earthjustice and the Rocky Mountain Climate Organization, has led the fight against climate change and its collateral damage. It has sued the federal government on behalf of bears, funded a landmark study on the collapse of alpine woods, and released a report on the warm-up in the West that reads like slasher sci-fi but isn't.

Skoglund, a supremely fit Ironman entrant who fell hard for the area on college fishing trips, has learned this landscape the honest way: by power-hiking its hills and rowing its rapids. Giving me a day to reset my lungs to the air at elevation (Yellowstone's low point is a mile above sea level; its mountains can reach 11,000 feet), he arranged for a bird's-eye view of the park, flying in a pilot from Colorado. The wind was flapping hard when we boarded a Cessna at an airfield near the town of West Yellowstone. Bruce Gordon, who's flown and photographed the West to document the damage done over the course of the past two decades, punched through thermal gusts as we banked and wobbled over the park's western rim. Below us were tracts of aspens framing Hebgen Lake, their gold crowns bending in the breeze. I started to praise their beauty, but Gordon stopped me: "Those are dead trees that rusted out. The drought and heat stressed them; then the bugs and spores killed them. From here to Colorado, there's miles of aspens gone, and for all we know, they'll never grow back again."

Indeed, in five years, more than half a million acres of young and old aspens in the Rockies have been nuked. The phenomenon is so new that it's inspired an acronym (SAD, or Sudden Aspen Death) but no clear means of reversal. Beetles and borer larvae, rarely seen at these elevations, have moved up the Rockies as the winters have warmed and feasted on the pulp of these regal trees. "Strip the bark," said Skoglund, "and you'll see tracks and channels where they've set up shop by the thousands. Then fungi enter through the holes the beetles carve and finish off the trees through infections."

Flying north, over the foothills of the Madison Range, we passed lodgepole pines whose evergreen crowns were the color of undercooked lamb. Shaped like closed umbrellas at a hundred feet tall, these, too, were desecrated by beetles, who carry in their mouths a vicious bacteria that drains the trees of sap and nutrients. Beyond the sick lodgepoles were legions of dead ones, their gray trunks tinder for trouble. Though Yellowstone's fire season used to end in September, three big blazes raged that morning, having burned through the weekend unchecked. "With winters ending early and summers stretching longer, you're getting bone-dry conditions that last for months," says Gordon, who, as founder of the nonprofit EcoFlight, flew arborists over Yellowstone dozens of times to compile the data on whitebark-pine death for the NRDC. "With all this deadwood, a couple of lightning strikes and there go thousands of acres."

In years of normal climate, or what used to pass for normal, summer fires served as reset buttons, purging old trees to make way for young ones and clearing new groves for herds to graze. But the decade of high heat here has set the stage for cataclysm: superfires that leap past all containment. Montanans speak grimly of the summer of 2000, when the Bitterroot National Forest lost a fifth of its acres to 100 new fires a day, and of 1988, when a third of Yellowstone's trees were devoured in a months-long inferno. Dire though those were, things could have been worse. "The Big Blowup of 1910 basically leveled Montana, burning everything in sight, including towns," said Skoglund. "Everything's in place for another fire-of-the-century event. All we've lacked – so far – is gale winds."

Past the town of Gardiner, we crossed the Gallatin Mountains, their brown pates glinting like copper pots. Twenty years ago, these peaks were crowned with snow no later than mid-October and, packing drifts up to 10 feet, were closed to hikers. Now people climb them in shorts and Tevas clear through Columbus Day. Gordon swooped in closer, to a couple hundred yards of the tree line; there, as ragged as week-old stubble, stood vistas of whitebark pine. Even in health, they are queer-shaped things – tall, gnarled stalks screwed into the hill, with crowns like Druids' hoods. These were far from well, though, either draped in red (dying) or the end-stage gray of rigor mortis. "Seven years ago, this was solid green. Now it's all deadfall and ashes," muttered Gordon. "It's like the roof's blown off and the animals have fled. But where do they go – where do any of us go – when it's all this gray down there?"