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In Southwest, Worst-Case Fire Scenario Plays Out

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Third of a five-part series

As the Earth's average temperature creeps upward, climate scientists have predicted record heat waves and droughts. That's what we've seen this summer in the U.S.

The question has become, are we now seeing the real damage climate change can do?

I drove though New Mexico's Santa Fe National Forest with ecologist Craig Allen, from the U.S. Geological Survey. Allen is energetic, restless and deeply worried about this forest. He has watched a triple combination of heat, drought and wildfire devastate this place over the past 15 years.

We stop by what once would've been a beautiful meadow full of Ponderosa pine — a tall tree with cinnamon bark and branches at the top, loaded with pine needles. But the big valley is badly burned. There are no live Ponderosa pines.

"The shrubs have basically taken control of the site," Allen says.

Ecologists call this "type conversion." The forest turned to shrub land. Big wildfires did that.

Heat waves, droughts and fire are not unusual here: A 16th-century mega-drought pushed the Pueblo Indians out of these mountains. And the current drought, in fact, is only the eighth most severe in the past 1,000 years.

But scientists say something is different now. The weather pendulum that swings back and forth between hot and cold, wet and dry is swinging more toward the hot and dry side.

"What we have now is a gradual trend towards warmer temperatures," says Park Williams, an ecologist at the Los Alamos National Laboratory in New Mexico. He says climate change is exaggerating the normal swings in weather.

"So each drought will be a little more intense, and each very good period will be a little less good for the foreseeable human future, it seems," he says.

Drought And The 'Sponge Effect'

Higher temperatures will mean more drought.

It works this way: Prolonged heat turns the atmosphere into a sort of dry sponge — a sponge that sucks more and more moisture out of the ground and out of trees. Scientists call this "sponge effect" the atmosphere's "vapor pressure deficit." Williams says this year, that deficit has increased here by 50 percent.

"Thinking about a 50 percent increase in vapor pressure deficit is like thinking about the Southwestern United States being transplanted onto another planet," he says.

Williams says that deficit will get worse as average summer temperatures increase.

Williams and Allen work within the Bandelier National Monument in the Jemez Mountains. It's a national park. It's rainy season now, and a small river runs through the woods.

But the rain is deceiving. Less rainfall and more heat are changing the landscape. Allen says the current drought almost wiped out one of the park's iconic trees, the pinon, 10 years ago. The pinon gives the Southwest its signature peppery scent.

"This is a huge change almost overnight in an ecosystem. The dominant tree on this site wholesale died," Allen says. "More than 95 percent of the mature pinon in Bandelier died."

This wave of heat, drought and fire has swept over the Colorado Plateau — a region of high mountain forests that stretch across Utah, New Mexico, Arizona and Colorado.

To make matters worse, the weakened trees are ever more vulnerable to bark beetles that now infest these forests.

Seeing 'The Worst Thing ... We Expected Would Happen'

Thomas Swetnam at the University of Arizona studies the forests of the Southwest. Like many ecologists, he says one reason forests are burning hotter now is because they're overgrown. For a century the U.S. Forest Service suppressed all fires, and now they're tinderboxes.

But Swetnam says climate change has made the situation much worse. And that's exactly what the computer models of climate change predicted.

"When you have predictions and the scientific understanding tells you this is likely what's coming, [and] then it starts to happen, the pieces, the dots are obviously connectable that it's very likely [we are] seeing the worst thing that we expected would happen," Swetnam says. "Warming is occurring and it's starting to take out our forests."

Back at Bandelier in New Mexico, Craig Allen's office sits deep in a canyon in the Jemez Mountains. He's watched four fires burn about 90 percent of the east side of the mountains in 16 years.

"For me, the really profound piece of this is the ability of the trees that have been growing for centuries on these hill slopes," he says. "Are they going to be able to survive even another 20, 30 years if the temperature increases?"

Inside, Allen's desk is surrounded with notebooks — 30 years of his field notes here. But now, he says, the forests they describe will probably never look the same.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.

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