Why: In 1850, Montana's Glacier National Park had 150 glaciers, a number that has dwindled to just 25 today. In about 15 years, glacier recession models predict none will remain. And while the park is famous for retaining nearly all of its native plant and animal species – including the grizzly bear – the ecosystem could change dramatically when the glacier-fed cold water is gone. Also, arguably the park's chief tourist draw, the glaciers, will be gone. "Many of the glaciers there today have lost more than half their volume in the last 20 years and are the disappearing gems of the National Parks System," says Dr. Bruce Molnia, a researcher with the U.S. Geological Survey. "It will soon be called Glacierless National Park."

What to do: The trip to Glacier National Park is a scenic 150-mile road trip from Missoula, Montana. Visitors can also fly into Glacier Park International Airport and drive or shuttle the 30 miles to the park's West Entrance. Glacier is open year-round, but the majority of the facilities are only open during the official season – late May to early September. Book the Glacier National Park tour with Natural Habitat Adventures, which takes a small group of seven people on a whirlwind trip through the park. Throughout the seven-day trip, you'll cruise across Two Medicine Lake, hike up to the summit at Logan Pass, and see active glaciers, not to mention grizzlies, whistling marmots, and waterfalls.

More Info: nps.gov/glac