FLAGSTAFF, Ariz. — Just outside this mountain town, where acres of ponderosa pines turn into a Christmas-green blur, Tom Whitham eyes the weary, struggling forest.
Death is everywhere. Their limbs bare and bark brittle, the trees quickly turn this forest into an aching reminder of the devastation of drought and a massive bark beetle infestation.
Whitham pulls over his pickup truck and gestures to the dead trees -- 75% in this area alone.
Forget talk of global warming and speculation of what it might do in 50 years, or 100. Here and across the West, climate change already is happening. Temperatures are warmer, ocean levels are rising, the snowpack is dwindling and melting earlier, flowers bloom earlier, mountain glaciers are disappearing and a six-year drought is killing trees by the millions.
Most scientists agree that humans are to blame for at least part of that warming trend, but to what degree?
"That's the $64,000 question," said Whitham, a regents' professor of biology at Northern Arizona University. "If we aren't causing it, we're certainly contributing to it. Humans can take a drought and make it even worse."
The West is unique in that it depends so heavily on the snowpack for its water -- three-fourths of the water in streams comes from melting snow. Over the past 35 years, temperatures throughout the region have inched up between 1 and 3 degrees, causing the snow to melt as much as three weeks earlier, said Kelly Redmond, regional climatologist for the Western Regional Climate Center in Reno, Nev.
Lilacs and honeysuckle bloom up to 10 days earlier. Warmer temperatures lead to a huge surge in woody plants that thrive in warm, wet conditions. Glaciers are retreating, roads are buckling in Alaska and shifting some supports on the 800-mile trans-Alaska oil pipeline. Already low reservoirs are called upon to water fields and quench thirst for longer periods after the seasonal snowpack is gone.
"The West has become habitated because of the ability to store and have a reliable water supply," said Martin Hoerling, research meteorologist with the National Oceanic and Atmospheric Administration's Climate Diagnostics Center in Boulder, Colo. "Simply, the temperature effect is going to put a much greater strain on water availability."
An earlier spring would lengthen Western farmers' growing season, but less water and warmer temperatures would mean that crops might not have the moisture to last until late summer, said Anthony Fisher, professor and chairman of the Department of Agricultural and Resource Economics at UC Berkeley.
Bennie Hodges, secretary-manager of the Pershing County Water Conservation District in rural Nevada, said the drought has forced him to allot farmers such a meager amount of water that they can only farm a fraction of their land. The county's reservoir is at 17% capacity.
"We're in tough shape here. Is it global warming? I don't know," Hodges said. "When you're in the desert, the wet and dry cycles come and go. I ask myself many times, 'Are we having global warming?' What do we do? We just try to get through."
Many scientists blame greenhouse gases such as carbon dioxide and ozone for causing global warming because the pollutants tend to trap the sun's heat in the atmosphere.
But some contend that the warming is just natural climate variability and humans have nothing to do with it.
Environmentalists preach conservation, especially with an uncertain snowpack and peak runoff occurring earlier. If that continues, "you would have a real problem that the current reservoir systems aren't designed to deal with," said Daniel Lashof, science director of the Natural Resources Defense Council's Climate Center.
"It's sort of like a cancer," he said. "We still have an opportunity to avoid the most severe consequences, but we have to act now."
Mike Wagner saw it coming. He predicted a beetle outbreak years ago in northern Arizona when he saw how abundant older trees were in overcrowded forests. When the drought began, the beetles were ready.
By 2002, trees weakened by drought were unable to fend off the beetles, and they were soon overcome. Tens of millions of trees across the West have been killed at a rate never seen before.
"Absolutely unprecedented," said Wagner, a regents' professor of forest entomology at Northern Arizona University. "We've never had these conditions before, never had that combination."
Scientists expect another devastating beetle outbreak this year.
Warmer temperatures only help the beetles reproduce more quickly, leading to more tree mortality. Some types of beetles that used to propagate two generations in a year now can produce three.
"This is all due to temperature," said Barbara Bentz, a research entomologist with the U.S. Forest Service who is studying bark beetles. "Two or three degrees is enough to do it."
Outside Cody, Wyo., an entire forest has been killed by the drought and beetles.