DUBOIS, WYOMING - Millions of trees are dying in the forests surrounding Yellowstone and Grand Teton National Parks. An epidemic of pine, spruce, and Douglas Fir beetles are killing the trees. They're also threatening a system that supports grizzly bears and other wildlife.

Pine Beetles are attacking here in the Union Pass area of the Wind River mountains. Where a lush green forest once stood, an aerial view shows huge patches of red mark dying pines. Most are lodge pole pines. But, the high mountain stands of white bark pine are dying, too in large numbers here.

As a scientist cuts the bark off a tree, he announces, "This is a dead tree. Attacked this year." A group of scientists examine the trees. They find pine beetle tracks under the bark of dead white bark pines, and nearby they find dead beetles. Then, they find beetles and tracks in a big green tree. They call this tree a zombie. While it's needles are green now, they'll be brown soon.

An Entomologist from the University of Montana, Dr. Diana Six said, "We're seeing effects all over the world. We're seeing effects in Mexico, Canada, all over the western U.S." Six explained the beetle populations are exploding because the winters are warmer, and summers are longer and warmer.

"We're seeing the beetles having large effects in an ecosystem where they previously did not." The ecosystem she's describing is the white bark pine system. It supports grizzly bears fattening up for the winter. They eat the fat and protein rich cones red squirrels stash in middens.

Ecologist Dr. Steven Running says global warming is a result of human acitivies creating too much carbon dioxide. Running said, "We are instigating changes in a matter of decades that normally would have occurred over thousands of years."

But, a geologist in Cody says dramatic climate shifts have occurred many times throughout earth's history. Leighton Steward said after much study, "I cannot find evidence that CO2 has been one of the major drivers of climate."

Steward has written a book on his theory, that throughout the eons, CO2 is caused by global warming, and is not the cause of it. He says scientists from several countries have studied ancient ice cores, and found, "That temperatures changed, and several hundred years later, the CO 2 levels changed." But, Dr. Running was one of 600 scientists from around the world on the Intergovernmental Panel of Climate Change that was awarded the Nobel Peace Prize for their 2007 report.

He warned, "We don't think another hundred years of this will end up with a functional biosphere anymore." The geologist's explanation of climate change can be found the in the newly released book, Fire, Ice, Paradise. The IPCC 2007 report on climate change can be found on the web.