DILLON, Colo.—Dan Gibbs keeps dead beetles in the back of his beat-up Chevy Silverado. He has a wooden block with beetles impaled on it, each insect about the size of a grain of rice. He’s got vials of embalmed beetles and their larvae. He carries around pieces of wood that show what those tiny beetles do to a mature lodgepole pine: They drill deep into the trunk and infect the tree with a fatal fungus that stains its wood blue.
Gibbs isn’t a scientist. He’s a commissioner for Summit County, a high-altitude slice of Colorado that’s gaining fame as a ground zero, of sorts, for an epidemic that has devastated pine forests across North America. Twenty years ago, the mountainsides around Dillon were a lush green; these days, they’re gray with needle-less trees.
The pine-beetle epidemic provides perhaps the most visual evidence of climate change in the United States. But that evidence, while arresting, remains circumstantial. Scientific studies linking the factors that drove the epidemic to rising global temperatures haven’t convinced everyone, let alone prompted people here to forsake fossil fuels.
It isn’t just the dead trees. Here, near the headwaters of the Colorado River, the snow is melting earlier—and there’s less of it. Summers are drier. Threats of wildfire and water shortages have grown, changing lives and livelihoods in Colorado and across the West.
Still, it’s not simple to draw a bright line from observable phenomena to climate change. For some policymakers, the lack of clarity is frustrating. Mounting evidence that the planet is warming and that human activity is to blame hasn’t generated any sort of political momentum for action, even as, in places like Dillon, forests are dying in plain sight.
As people here struggle to understand the beetle epidemic, the term “climate change” has become so inflammatory that few even utter it. It’s also unclear to residents what, exactly, they would accomplish by reducing their fossil-fuel use. Without a more far-ranging plan of attack on a national—indeed, international—scale, all that people in Dillon and places like it can do is adapt to changing circumstances.
Gibbs keeps beetles in the back of his pickup to teach people about forest health, not to start a conversation about climate change. (And he, like almost everyone in the mountains, drives a gas-guzzling truck.) “Does climate change play a role in it? For sure, I think,” Gibbs said of the pine-beetle epidemic. But, he added, “I think scientists are still really studying it.”
DEEP IN THE FOREST
John Mack has a saying: “These trees are dead; they just don’t know it.” Along a back road to a campsite in Rocky Mountain National Park, the chief of resource stewardship at the park points out seemingly healthy trees covered in ugly, popcorn-shaped masses, a lodgepole pine’s natural response to the mountain pine beetle. A healthy tree can forcefully push burrowing beetles out, but many of Colorado’s pines are water-stressed and aging. Beetles have mass-attacked them, an onslaught that can overwhelm even healthy trees, Mack says.
North America is witnessing the largest pine-beetle epidemic in recorded history. From Canada’s Yukon Territory to New Mexico, pine trees by the hundreds of millions are succumbing to a fungus that the beetles carry. The pine needles of infected trees first turn a violent red, then they fall, and, finally, the dead tree topples over. Year by year, communities have watched a scourge advance across mountainsides and through neighborhoods, trees turning from green to red to gray. The beetles now attack 12 pine species, from the high-elevation whitebark pine to the lower-elevation ponderosa and piñon. The blight has devastated 3.3 million acres in Colorado alone since the 1990s.
Beetles kill, die off, and regenerate, all of which is part of a lodgepole pine forest’s natural life cycle. But human activity helped set the stage for the current epidemic. Decades of fire suppression have left the West with dense stands of vulnerable, elderly trees. Climate has also played a role. Frigid winters that usually kill the beetles have become, over the past 20 years, the exception rather than the rule. Earlier snowmelt and longer summers have altered the beetles’ range and life cycle; they now attack pines at higher altitudes and latitudes, and they reproduce twice a year instead of once. Earlier springs and a series of dry years have also weakened trees, turning them into ideal beetle food.
Among the scientific community, a consensus is growing that changes in climate have propelled the outbreak. Jeff Mitton, an evolutionary biologist at the University of Colorado (Boulder), has been studying the mountain pine beetle for more than 30 years. There’s no doubt in his mind that climate change has driven the infestation.
“The question is, why has this gotten so much worse?” Mitton said, with the placid gaze of a man used to thinking about long stretches of evolutionary time. “The beetles are out six weeks to two months earlier because springtime temperatures are warmer.” Mitton connected the epidemic to other changes observed in American landscapes, from melting glaciers to shifting agricultural regions to increases in global temperatures.