GLACIER NATIONAL PARK, Mont. - Age has not been kind to Glacier National Park. The gorgeous million-acre park in northwestern Montana celebrated its 100th birthday on Tuesday. But many of its glaciers have melted, and scientists predict the rest may not last another decade. The forests are drier and disease-ridden, leading to bigger wildfires. Climate change is forcing animals that feed off plants to adapt.

GLACIER NATIONAL PARK, Mont. - Age has not been kind to Glacier National Park.

The gorgeous million-acre park in northwestern Montana celebrated its 100th birthday on Tuesday. But many of its glaciers have melted, and scientists predict the rest may not last another decade.

The forests are drier and disease-ridden, leading to bigger wildfires. Climate change is forcing animals that feed off plants to adapt.

Many experts consider Glacier Park a harbinger of Earth's future, a laboratory where changes in the environment will likely show up first.

"What national parks all give us is, in effect, a controlled landscape where we can see the natural and climatic processes at work," said Steve Running, a University of Montana professor and co-recipient of the Nobel Prize in 2007 for his work on climate change.

Average temperatures have risen in the park 1.8 times faster than the global average, said Dan Fagre, a U.S. Geological Survey scientist.

The change is visible to the naked eye, with the vast moraines left behind as the giant glaciers melt away. Climate change is blamed for the increasing size and frequency of wildfires, and lower stream flows as summer progresses.

What this all means for the bears, wolves and other big predators in the park is unclear, Fagre said.

A birthday ceremony Tuesday focused on the wonders of the nation's 10th national park. Several hundred tourists and employees listened in the crisp mountain air as speakers extolled its virtues as one of the most intact and diverse ecosystems in the world.

"Glacier connects us to the very core of our nature," park superintendent Chas Cartwright said.

Glacier remains perhaps the only place in the Lower 48 where all the big wild animals that Lewis and Clark saw in 1804 can still be seen, Running said.

"Our landscapes are still wild and pristine and clean," he said. "When you start looking globally at how many clean, wild landscapes are still around, Glacier is doing pretty well."

Glacier, signed into law on May 11, 1910, by President Taft, draws 2 million visitors per year to see its sawtooth peaks, clear lakes and wildlife. Nearly all come in the summer, jamming the signature red buses on Going-to-the-Sun Road, the dizzying roadway that bisects the park.

"We come to Glacier as often as we can," said Shirley McLaughlin of Missoula. "I have a real sense of ownership."

The park drew 4,000 visitors in 1911, when tourists would ride the train to Glacier and travel by horseback to stay at chalets in the high country, said Amy Vanderbilt, park spokeswoman. Visitors come to see predators like grizzly bears, which are now stable around 300, she said.

But the same cannot be said for the park's iconic glaciers, giant slabs of ancient ice that crawl slowly down the face of mountains, gouging spectacular landscapes.

Fagre said that based on geologic evidence, the park had about 150 glaciers in 1850, the end of the so-called Little Ice Age. Most would have still been around when the park was established in 1910.

Only about 25 named glaciers are left, and they could be gone by 2020, Fagre said.

Rising temperatures also mean spring is arriving about three weeks early, which causes winter snow to melt earlier and forests to become drier as the summer progresses, said Jack Potter, chief of science at the park.

That has led to bigger and more destructive fires, in part because insect infestations have weakened trees, Potter said. There are now fires at higher elevations, too, because the tree line is moving higher as temperatures rise, he said.

Less moisture means lower stream flows, which endanger fish species, he said. The vegetation is changing, providing less food and protective cover for animals.

The chance to see the glaciers that are now disappearing is what lures many visitors to the remote park.

But tourists won't necessarily notice the glaciers are gone, because there will still be snow on the peaks of many mountains, Running said. And most of the remaining glaciers are located in the back country, far from visitors who stick to the main roads and lodges.

But it's hard for people to imagine Glacier National Park without glaciers.

"The day that Glacier National Park officially announces there are no glaciers left, it will make worldwide headlines," Running said. "When people find out I am from Montana, that is the first thing they ask me: 'Is it true about Glacier National Park?'"