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Fire, Rock Slides, and Floods: UN Report Details Growing Warming Threat in the Mountains

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Inmate firefighters battle the Ferguson fire in Jerseydale, California, on July 22, 2018.  (Noah Bergern/AFP/Getty Images)

With ominous orange-gray smoke clouds seething on the western horizon, it’s easy to understand how Colorado’s highest city and other mountain communities are directly threatened by global warming. 

Mountain snowpack is shrinking and melting earlier in the spring. Warmer and longer summers dry out vegetation and increase the threat of wildfires in western mountain forests, where the fire season has lengthened by at least a month since 1979.

The growing wildfire risk is just part of an accelerating cycle of global warming impacts in the world’s mountain regions, according to a new Intergovernmental Panel on Climate Change report that includes a section focused on mountains for the first time in more than 20 years.

“Snow cover duration has declined in nearly all regions, especially at lower elevations, on average by five days per decade,” the mountain chapter of the IPCC report says. On average across Western North America, the European Alps and High Mountain Asia, temperatures are warming by 0.54 degrees Fahrenheit per decade.

That’s melting glaciers and changing mountain river flows, disrupting plants and wildlife, and increasing the risk of extreme rockslidesavalanches and mountain floods caused by rain falling on snow.


Taken together, global warming impacts represent an existential threat to millions of people in the Andes, the Himalaya, the European Alps, and the U.S. Mountain West including Alaska, said Heidi Steltzer, a biologist at Fort Lewis College in Durango, Colorado, and a lead author of the mountain chapter.

“Shrinking glaciers and snow harm Indigenous Peoples and rural communities greatly. Concern, commitment and action on climate change should not depend on which places, species or people are impacted. Instead, they should be motivated by compassion,” Steltzer said.

Water Reliability 

In Crested Butte, about 100 miles southwest of Leadville, hydrologist and physicist Rosemary Carroll studies how disruptions to the water cycle will affect local ranchers and ski areas, as well as drinking and agricultural water supplies hundreds of miles away.

The IPCC assessment found that global warming will change the timing and amount of runoff, “affecting water storage and delivery infrastructure around the world,” a finding backed by research focusing on the West.

A 2016 study in six Western mountain ranges showed rising temperatures will shift the snow accumulation zone and runoff timing enough to have significant impacts on water cycles. And some towns in the Rockies and Sierra Nevada are at risk from dangerous flash floods as global warming brings rain, rather than snow, to some mountain regions.

Carroll pointed out her living room window to a craggy ridgeline where she measures how water from melted snow trickles through rocks and meadows down to the East River, on to the Gunnison River and finally into the mighty Colorado.

“The new normal is that the snowpack is melting earlier and we have earlier runoff, and that’s a fact. There’s going to be less water for a given snowpack,” she said. Even in average snowfall years, global warming is reducing the amount of available water for irrigation and storage, she said.

Her research for the University of Nevada’s Desert Research Institute and the U.S. Department of Energy will help communities adapt as global warming disrupts flows from mountain streams. Around Crested Butte, the ski industry and local ranchers will feel the changes first.

But addressing those impacts isn’t as easy as just throwing a new report on the table. Translating science into action requires working with stakeholders from the start.

“Ranchers know what’s happening, they know that things are shifting, but they’re afraid the policy will shift in a way that they will carry the burden of the change. Since they have most of the water, they fear they will have to give up the most, and that it won’t be equitable,” she said.

The states that get their water from the Colorado River are already restructuring water-sharing agreements to stave off shortages and trying to develop new storage plans to account for extreme wet and dry years.

Goodbye to Glaciers

Global warming will change nearly every mountain ecosystem, starting with the very visible meltdown of glaciers.

In the European Alps, some glaciers retreated by as much 410 feet last year — imagine the Empire State Building shrinking by a third. Globally, the world’s glaciers have lost 9 trillion tons of ice since 1961, raising sea level by about 1 inch, according to the European Space Agency.

As glaciers melt, they create a series of risks: newly formed meltwater lakes can burst through their banks, flooding towns and farms below. And as the ice dwindles, that will significantly change the timing and amount of water available for hydropower production and agriculture.


Along with disrupting ecosystems and downstream communities that rely on glacier meltwater, global warming in the mountains will cause emotional and cultural loss as cherished landscapes vanish. In Switzerland, people recently held a memorial service for the disappearing Pizol Glacier as a way of dealing with that grief, a sometimes overlooked component of climate resilience.

The physical threats are real and growing, said Swiss glaciologist Matthias Huss.

If greenhouse gas emissions peak in the next few years and then start to decline, glaciers in the European Alps will lose two-thirds of their current ice. With continued high emissions, the glaciers will all but vanish, with only 5 percent of the current ice remaining, Huss and colleagues found in recent study.

An increase in rockfall events, and flooding from glacier lakes, also due to more extreme weather events, is likely,” Huss said. “I think European countries are prepared, and they have the financial means to adapt. It will be much more difficult for developing countries to adapt to the challenges in mountain regions.”

Extreme storms that destroy forests and damage roads and railroad lines could also become more frequent in the world’s mountains, although climate models aren’t yet localized enough to project such changes accurately, the IPCC assessment concluded.

It won’t be cheap to redesign and rebuild water infrastructure, Huss said. In some snow-dependent communities, the meltdown will also drive wrenching cultural and economic changes. But “one could also see this as a chance for major development toward a more sustainable way to live on our planet,” he said.

Adapting Food Crops

That’s what University of Colorado researcher Tsegay Wolde-Georgis was thinking when he led a project in the early 2000s to cultivate apple trees around Atebe, in the dry highlands of Ethiopia where he grew up.

Diversifying local food supplies will help make the region more resilient to global warming, he said. The new IPCC assessment affirms that global warming is driving dangerous changes in mountain environments that threaten food supplies. But along with warnings, the world needs action, he said.

“Everything is getting more extreme, and there is seasonal confusion,” he said. But there is enough scientific and traditional knowledge to find on-the-ground projects and do them, he said.

For the apple orchard, he adapted a traditional permaculture technique, using water-filled clay pots to efficiently irrigate the young trees. At the same time, residents enhanced the water-holding capacity of deforested hillsides by building terraces and planting vegetation.

Such regenerative agriculture is crucial for food security in developing countries, said Wolde-Georgis, who works with the Consortium for Capacity Building, part of the University of Colorado’s Institute of Alpine and Arctic Research.

After decades of academic research and projects, he radiates the kind of practical wisdom that can help shape resilience to global warming. His eyes gleam as he recalls the look on a local priest’s face during the first apple harvest.

“It was the first time in his life he tasted an apple. When we plant apples, it’s mitigation [of the climate impact], but at the same time, we are solving problems. We have to find something that’s doable on the ground,” he said. In four years, the farmers planted 1,400 apple trees.

At the same time, communities worked to restore watersheds by building terraces and replanting clear-cut hillsides. Wolde-Georgis said the work was successful. Streams that had been dry by the end of December now hold water through the end of May.

On a larger scale, Wolde-Georgis helps build physical and information infrastructure to boost resilience, including new roads and railroads to help transport food when climate extremes cause crop failures.

Ethiopia and other developing countries also need more institutional science-based infrastructure to inform good governance across jurisdictional boundaries, he said. To meet the challenges ahead requires working in an atmosphere of trust and a spirit of collaboration, he said.

Disrupting Plants

At the Rocky Mountain Biological Lab in Gothic, Colorado, David Inouye’s cabin near a patch of shimmering gold aspens is marked by wisps of chimney smoke. For nearly 50 years, he’s been recording plant and animal activity while other observers tally snowfall and snowmelt data day by day — a scientific deep dive into time and space.

Compared to the 1970s, spring is coming earlier. There is more winter rain, and summers are longer and drier. It all adds up to disruption for mountain ecosystems, where most plants only have a few weeks to bloom. And the plants are tightly linked with pollinating insects in a delicately timed cycle.

“The ecology of this altitude is driven largely by how much snow we get in the winter and when that snow melts,” Inouye said. “As the climate changes, we’re tending to get less snow and warmer and earlier springs. A paradoxical consequence is that we’re getting more frost damage,” he said. The effects ripple through the ecosystem as global warming disrupts plants and seed production, which, in turn, means less food for small mammals and birds.

Graceful yellow glacier lilies are blooming 17 days earlier than they did in the 1970s, but migrating hummingbirds that depend on the flower nectar aren’t keeping up. By the time they arrive, many of the plants have withered away, and if current trends continue, in two decades the hummingbirds will miss the first flowers entirely. Ecosystems could collapse as global warming continues to decouple complex ecological relationships, showing why global warming is a threat to biodiversity.

Another study documented how earlier spring snowmelt makes mountain daisies bloom earlier, when they are more susceptible to frost. The research showed how the frost damage reduces the amount of nectar for a species of butterfly that depends on that particular flower for feeding during the egg-laying season.

“If they don’t get nectar, they can’t make eggs, and the population declines,” Inouye said.

Tipping Points

The research at the Rocky Mountain Biological Lab helps connect the dots in complex ecosystems and how global warming can make them unravel, said lab executive director Ian Billick.

“What people don’t realize is that we’re changing multiple things at the same time. People don’t realize how drastically things are going to change,” he said. Massive disturbance events linked with global warming like the early 2000s bark beetle outbreak that killed trees across millions of acres will happen again and again. Multiple stressors are driving mountain ecosystems past tipping points, leading to fundamental change, he said.

“Our agricultural productivity depends on these ecosystems functioning in a highly integrated way, so it’s like if you throw a screwdriver in the middle of an engine, the whole thing falls apart, and I think it’s like with ag, where these finely tuned things are going to fall apart.”

The IPCC report represents only the tiny tip of a “massive global change iceberg,” said Steltzer, the Colorado biologist and lead author of the mountain chapter.

“Nine-tenths is what we haven’t seen, measured and documented. We know things are changing for which we have no peer-reviewed scientific articles, and things are changing too fast to keep up,” she said. “There’s no reason to wait to act. We know enough.”

Just this past winter, both Europe and parts of the Rockies experienced unprecedented avalanche cycles after record snowfalls, surprising scientists as well as public safety managers charged with keeping mountain roads open. Recently, mosquitoes that carry West Nile Virus have been appearing in the high mountains but remain largely untracked, along with other invasive species. And there are likely scores of other ecological cycles being disrupted that haven’t been studied at all, Inouye said.

The IPCC assessment also concluded that forest fires are likely to increase in mountain areas where summers become warmer and drier. “Coastal ranges of California, the Blue Mountains of Australia, Mt. Kenya, and mountains on the fringes of the Mediterranean Sea, already subject to frequent fire episodes, would be severely affected,” the assessment said.

A 2019 study showed that the fivefold increase in the extent of California’s wildfires since the 1970s was “very likely driven by drying of fuels promoted by human‐induced warming.”

“Snow is decreasing, temperatures are warming, and mountains are changing in ways I never expected I’d live to see,” Steltzer said. “Policy-makers ask for data to show how bad it is. … Instead, they could ask how do we preserve the benefits of nature for each of us and all of us.”

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