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 Tuesday. But many of its glaciers have melted, and the rest may not last another decade.

The forests are drier and disease-ridden, leading to bigger wildfires. Climate change's effect on plants is forcing the animals that rely on them to adapt.

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

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

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

"Our landscapes are still wild and pristine and clean," he said.

Glacier (nps.gov/glac) draws 2 million visitors a year to see its sawtooth peaks, clear lakes and wildlife such as grizzly bears, which are now stable at around 300.

But the same cannot be said for the park's iconic glaciers 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.

It's hard 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.