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September 2007

How Climate Change is Affecting Our Alpine Environments

Thanks to melting ice and snow, climate change is effecting the future of our mountains

If you love mountains–and the glaciers, snowfields, and alpine meadows that cling to their slopes–better grab your pack now. Climate change is melting ice and snow as we speak, making these high, cool places the most visible warnings of a warming world. Why should you care? In addition to altering the scenery and jeopardizing vulnerable species in iconic parks, rising temperatures threaten access to the peaks and ridges you love to hike. Plus, what happens in mountains directly affects lowland habitats and ecosystems many miles away. Here’s an overview of the key changes scientists are tracking.

1. More frequent debris flows
Ranges in the Northwest will see more and stronger winter storms, like the 2006 deluge that dumped 18 inches of rain on Mt. Rainier.
When glaciers retreat, they deposit moraines of loose rocks and soil in steep valleys. Heavy rain erodes these unstable slopes, mixing runoff and debris into powerful floods that can wipe out trails, roads, and bridges, says Paul Kennard, a river geomorphologist at Mt. Rainier National Park. Destructive debris flows can occur in any season, but peak in late fall and early winter, when there’s little snow to absorb and slow runoff. A 2005 study predicts a 140 percent leap in “extreme precipitation events” in that November-to-January window in the Pacific Northwest over the next 100 years.

2. Thirstier hikers
Retreating mountain glaciers will reduce meltwater flows to downstream drainages.
The glacial runoff that quenches your thirst and sustains Western trout populations will diminish as ice sheets in the Pacific Northwest continue to recede. Annual summer flow in North Cascades National Park‘s Thunder Creek, the most heavily glaciated drainage in the Lower 48, has decreased by 30 percent in 150 years. Nearby Mt. Baker’s Deming Glacier has retreated 1,000 feet since 1987, endangering the 20 percent of summer stream flow it supplies for the city of Bellingham. As glacial runoff slackens, river crossings will become easier, but some important water sources for hikers and animals miles downstream will dry up.

3. Higher alpine zones
Plant and animal species endemic to Appalachian and Rocky Mountain peaks will be squeezed out by encroaching vegetation.
Species adapted to alpine zones can’t easily migrate up or down slope, which makes them vulnerable to climate change. That could create trouble for Southern Appalachia’s bald peaks and New England’s alpine ridges, as rising temperatures push treeline higher. Most endangered are rare wildflowers like diapensia and alpine azalea in New Hampshire’s White Mountains, and northern flying squirrels and salamanders in the Great Smokies. In the West, bighorn sheep, raptors, pikas, mountain goats, marmots, and many wildflowers won’t escape the advancing foliage and rising temperatures.

4. Stronger avalanches
Warming temperatures will increase the frequency and strength of snow slides across the country.
Two winter climate trends–more precipitation falling as rain, and more freeze-thaw cycles–will increase the number and intensity of avalanches, making it harder for hikers and skiers to predict them. Scientists also fear that new slide patterns will alter the existing treeless chutes that avalanches scour into mountain slopes. Plants like cow parsnip and glacier lily flourish in these niche habitats, providing dependable forage for grizzlies and bighorn sheep.

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