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How warming is killing off the trees that helped keep us cool

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Climate Cast
Every Thursday, MPR meteorologist Paul Huttner joins The Daily Circuit to talk about the latest research on our changing climate and the consequences we're seeing here in Minnesota and worldwide.
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Trees, with their ability to store carbon, are an important buffer against climate change. So what's happening to the forests of the American West is alarming, in the view of meteorologist Paul Huttner.

  Huttner shared his concerns with Kerri Miller, who went hiking last weekend in Colorado and was disturbed by what she saw.

"I couldn't believe how devastated the pines are in the park," Miller said. "When we talked to the rangers about it, they told us it was the pine bark  beetles ... And they connect it to climate change."

"There is no doubt about it," Huttner replied. "Last summer I went out to the Black Hills and Yellowstone and the Tetons. I hadn't been out there in about 18 years. I was floored."

Huttner said he saw "entire mountainsides of dead tree stands out there. As much as 30 to 50 percent of the Black Hills is infested with the pine bark beetle. It is in fact very clearly linked to climate change. 

"Our Western forests, in the Rockies, [are] really now kind of a living and dying laboratory for climate change," he said. "It's because of the warmer temperatures, less snow in winter, that these beetles are able to survive and thrive, and the results are what you saw before you last week."

Pine trees killed by bark beetles
An aerial view shows pine trees killed by bark beetles near Strawberry Valley May 2, 2012 near Bryce Canyon National Park in Kane County, Utah. The insects have killed millions of pine trees across western North America in the last few years.
Ethan Miller/Getty Images

And Minnesotans should not imagine that the same problem won't come to their state. "The infestation started south and is spreading north," Huttner said. "I was in Arizona for nine years, I watched it happen there to the big Ponderosa pine stands. It's already moving through Colorado, making its way north into Yellowstone and the Black Hills and eventually into Minnesota. So as the climate continues to warm, the northward range of these beetles will continue to extend. That's one of the things we're concerned about here as well."

Reed Maxwell, an associate professor  at the Colorado School of Mines, said the damage to his state's trees is "really depressing."

"I mean, it's green mountains on our license plate. The pine trees and Rocky Mountains is almost synonymous with Colorado. There are certain areas where that's still true. But there are plenty of areas, particularly in Rocky Mountain National Park, where it's unbelievable devastation. 

"Currently, in the state of Colorado, the pine beetle epidemic  is at or past its maximum impact, and the estimates are that 95 percent of the mature lodgepole pines in the Intermountain West are dead."

Huttner described what he called a "vicious cycle": 

"So as the climate continues to warm, the northward range of these beetles will continue to extend."

"The climate gets warmer, less snow, early springs, hotter, drier summers. The trees become stressed; they can't fight off these pine beetles. It doesn't reach 30 to 40 below in winter like it used to, and that's what kills the larvae and these new beetles. And so these massive stands of trees are infected, they die, and entire mountainsides stand there dry and fire-prone, kind of a tinder box. Then fire is another mechanism that really changes the landscape. It sweeps through. Deforestation. And what grows after the fires may be different. More grasslands, more deciduous trees, and that's what we call a biome change, or a landscape change.

"And here's one of the scary parts for climate scientists: That change may not be as effective at pulling CO2 out of the atmosphere, because ...  these trees are great warehouses or stores of carbon. They suck carbon dioxide out of the atmosphere and hold it. When they burn, that is re-released into the atmosphere, and then those forests are not there to absorb it anymore."

And it is not only the Western trees that are burning. 

"We've been talking about the Intermountain Western forest," he said. "There's also the boreal forest, which we know starts in northern Minnesota. If you've been to the Boundary Waters, Ely, that's boreal forest. That ring of boreal forest runs around the planet from that latitude north to just south of the Arctic Circle. Well, guess what? Fires are increasing dramatically in those forests as well. They're burning faster than at any time in the last 10,000 years. That's a study from the National Academy of Sciences, it just came out on Monday.

"These forests cover about 10 percent of the earth's land surface. So as the black carbon is released from these fires —  think of it as soot — not only does it release more carbon into the atmosphere, but it also lands on snow cover in the Arctic, and that makes the snow and ice melt faster  because it absorbs sunlight more efficiently."

The Minnesota forest is already changing, Huttner warned, and will change faster as climate change accelerates.   

"People have used the term runaway climate change. I don't know if I'd go that far," he said. "But these feedback mechanisms, they can accelerate the pace of climate change. Because we're absorbing less CO2 from the atmosphere, so it's building up faster. We're releasing more CO2 through these massive fires. And we're also melting the Arctic faster, and the high mountain glaciers. And that's very important because as those glaciers, like in the Tetons and Yellowstone, begin to disappear, those are like a thermostat. ... That cooling mechanism just isn't there anymore."

Watch a video from the University of Colorado on pine bark beetles: