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.
5. Smoggier mountain skies
Rising temperatures could worsen air quality in New Hampshire's White Mountains.
Nitrous oxides and hydrocarbons from car exhaust combine on warm, sunny days to produce ground-level ozone, an oxidant that irritates the mucus membranes in humans and animals, and that damages plants. In addition to blanketing major cities, this smog accumulates in alpine regions like the White Mountains. As a result, ozone readings atop Mt. Washington are generally 2 to 5 times higher than at lower elevations. Because higher temperatures increase ozone production, global warming will continue to degrade the air quality and the views on the Northeast's high peaks.
6. Smaller glaciers
By mid-century, much of the permanent ice in America's national parks will have vanished.
Nearly all of the world's mountain glaciers have receded as average global temperatures have risen 1°F in the last century, according to the IPCC's Climate Change 2007 report. In our backyard, 60 percent of Sierra Nevada glaciers and 40 percent of the perennial ice in North Cascades National Park has melted since the 1880s. Because carbon lingers in the atmosphere for decades after it's produced, warming will continue even if emissions are cut. In the Pacific Northwest, the most glaciated region in the Lower 48, temperatures are predicted to rise another 1°F in the next 20 years, melting all but the high-elevation ice sheets, like those capping Mt. Rainier.
7. Soupier tundra
Melting permafrost could make Alaska hiking a nightmare and triple current atmospheric CO2 levels.
Eighty percent of Alaska's interior, including most of Denali National Park, rests on permafrost, a layer of frozen soil. Scientists predict that rising temperatures will thaw the top 10 feet of half of the Northern Hemisphere's permafrost acreage by 2050, aggravating existing damage to roads and buildings and turning solid tundra in prime hiking destinations into impassable bogs. Simulations run by the National Center for Atmospheric Research predict that 90 percent of the world's permafrost could turn to slush by 2100. The real danger, however, is the resulting release of underground methane, a greenhouse gas that is 21 times more potent at trapping heat than CO2.
8. Less snowpack
Sierra snow levels are thinning, and they're melting away three weeks earlier than they did 50 years ago.
Peak runoff for Yosemite's waterfalls is shifting from early summer (when most hikers visit) to spring, when many trails remain inaccessible. The earlier melt will also cause some streams to dry up in July, a month early. Even if we reduce CO2 emissions, forecasters believe California temps will rise 3 to 5.5°F over the next few decades, causing the Sierra snowpack to decline by 30 percent. If we don't, snowpack could shrink by 90 percent, ending most winter recreation and turning snow-fed streams into dry washes.
Alaska's Glacier Bay is buried under an ice sheet 4,000 feet thick and up to 20 miles wide.
Glacier National Park has more than 150 glaciers.
Rising temperatures in the Sierra Nevada cause peak runoff earlier in the year.
The Intergovernmental Panel on Climate Change (IPCC) is established.
The Paradise Ice Caves vanish from Mt. Rainier National Park as the Paradise Glacier retreats.
Mt. Rainier's glaciated area is 20 percent smaller than it was in 1913.
Aerial photos show that North Cascades National Park has lost 13 percent of its glacier area since 1971.
Glacier National Park has 73 percent less ice coverage than it did in 1850.
The IPCC predicts a global temperature increase of 2 to 11.5°F by 2100.
The last glaciers vacate Glacier National Park as mean summer temps hit 63°F. Meanwhile, Sierra snowpack is down 30 percent, threatening California's winter tourism industry and water supply.
Colorado Rockies snowpack declines 24 percent.
Half of the Arctic's permafrost acreage has melted to a depth of 10 feet. Spring runoff in Western rivers is down 10 to 20 percent.
Average temperatures in the Sierra Nevada have risen 4.5°F, advancing snowmelt runoff by another month.