GADMEN, Switzerland >> For hikers looking for a daylong outing in central Switzerland, the Trift Glacier footbridge is a popular destination. It’s a short gondola ride from the village of Gadmen, followed by a few miles’ trek up a rocky path overlooking a granite gorge.

Those who successfully fight off a case of nerves — the slender cable-and-plank bridge is more than 500 feet long and 300 feet in the air — are rewarded with spectacular views of the Trift Valley. But the glacier itself is hardly to be seen. Because of a warming atmosphere, it has retreated rapidly this century.

The Trift is a casualty of climate change, one of tens of thousands of glaciers around the world that are shrinking as the Earth warms because of greenhouse-gas emissions. But the Swiss have a plan to make use of the valley the ice left behind — by adding to hydropower production, which itself is threatened by glacial melting.

Worldwide, shrinking glaciers are adding to rising sea levels and causing floods, and will eventually mean less water for people and crops. But this great melting will also have an effect on the generation of electricity, as glaciers shrink to the point where meltwater flows start to decline. That will strain energy supplies since, worldwide, about 16 percent of power is generated by flowing water.

The potential impact is far greater here in Switzerland, in the heart of the Alps, which has more glaciers than any other Alpine country and where hydropower accounts for nearly 60 percent of electricity. (By comparison, the United States gets about 7 percent of its power from water.)

Rain and melting snow are often the main sources of water for hydropower, but in Switzerland and many other countries the melting of glacier ice is an important contributor. And those glaciers are now melting fast.

In Switzerland, where the Alps are warming faster than the global average, most of the country’s 1,500 glaciers have retreated every year since 2001; many are expected to all but vanish by 2090. The melting was especially bad in 2017, when 20 monitored Swiss glaciers lost about 3 percent of their volume because of a dry winter and an extremely hot summer. Last year was bad as well, according to Glacier Monitoring in Switzerland, which tracks changes.

As warming continues, plants like one in Bitsch, deep inside a mountain near the Rhone River, will most likely see a decline in power production this century.

At the Bitsch plant, electricity is produced by generators attached to three turbines that are spun by water from a reservoir 2,000 feet higher up the mountain. The reservoir, behind the 50-year-old Gebidem arch dam, is fed by the Aletsch Glacier, the longest in Europe.

But the Aletsch, 14 miles long and up to 3,000 feet thick, is shrinking year by year. It could lose 90 percent of its ice by 2100.

“When we designed the first power plants in Switzerland in the middle of the last century, we didn’t talk about climate change,” said Florian Widmer, an executive with Alpiq, a Swiss power company that is the largest shareholder in the Bitsch plant. Now, he said, companies like his must plan for a future of little or no glacial meltwater.

For now, accelerated melting in many glaciated regions, including the Alps, is increasing stream flows and filling reservoirs faster, leading to greater electricity generation. In Switzerland, for example, a recent study showed that loss of glacial mass because of the warming climate has increased hydropower production by 3 to 4 percent since 1980.

“Today, we benefit from glacial melting,” Widmer said.

But eventually the ice will retreat so much that stream flows will decline and power production will drop. Although climate forecasts suggest that, in coming decades, Switzerland might make up for some of its lost ice with increases in rain and snow, retreating glaciers are expected to lead to as much as a 5 percent decline in electricity production in some regions of the country.

Already, the need for environmental flows — releasing some water from dams to maintain the ecological health of a river — cuts into hydropower production. And Switzerland faces another problem of its own making: Amid widespread public opposition to nuclear power following the 2011 Fukushima accident in Japan, the Swiss government has pledged to gradually phase out the country’s five reactors. Those reactors provide nearly all the rest of Switzerland’s power, and they are especially important in winter, when hydropower production drops and energy demand increases.

The government’s energy strategy calls for increases in wind, solar and geothermal power, which currently make up a small share of electricity production. The Swiss are also counting on hydropower companies to expand their output, even though glacial meltwater will eventually decline.

For Alpiq and other companies, the land left behind by retreating glaciers offers opportunities.

When glaciers grow and advance, their abrasive power — the weight of massive amounts of ice mixed with rock debris — carves valleys in the landscape. As glaciers shrink, these valleys are exposed. Some of them may be ideal sites to collect and store water for hydropower.

Swiss researchers have studied the country’s glaciers and, using radar, the underlying bedrock, with an eye to locating potential new reservoirs. “We’re looking at what is going to be the future topography,” said Robert Boes, an engineer and director of the Laboratory of Hydraulics, Hydrology and Glaciology at the Swiss Federal Institute of Technology in Zurich.

Other criteria are evaluated as well, including potential construction costs, how much energy could be generated and whether the quantity of sediment — retreating glaciers leave a lot of that behind as well — would harm turbines or cause other problems.

One suitable spot is at the Trift. Another is at the Oberaletsch, a smaller glacier near the Aletsch.

A quarter-century ago, the Oberaletsch had about half a cubic mile of ice. It lost about 7 percent of that by 2000, and by the middle of this century the ice loss could be 70 percent of the original volume.

Although the Oberaletsch’s leading edge, or tongue, is still covered by up to 650 feet of ice, by the middle of the century the ice is expected to be gone and a long, thin lake will appear in its place. That will collect meltwater from what remains of the glacier, as well as runoff from rain and melting snow.

Engineers with Alpiq have proposed building a new generating plant at the existing Gebidem dam reservoir and tunneling up to a spot under the Oberaletsch where the lake will form. Everything, including the plant, would be inside the mountain to reduce the visual and environmental impact. Widmer said that the company was in discussions with government agencies about the project.

Water from the Oberaletsch would generate electricity at the new plant and then flow to the existing plant at Bitsch and make more electricity there.

At the Trift, the ice that once filled much of the valley is already gone, replaced by a natural lake. Another hydropower company has plans to make it even larger.

“We saw 10 years ago that it was a lake,” said Daniel Fischlin, chief executive of the company, Kraftwerke Oberhasli, or KWO. “That started the idea — there’s a really narrow place, and there you can build a dam.”

The dam would be built in the narrow gorge at the outlet of the lake, and would be higher than the existing footbridge. As with the Oberaletsch project, the water would travel by tunnel to a new generating plant farther down the mountain.

The reservoir and plant would serve as backup power, in effect, for periods when electricity shortages threaten to destabilize the power grid. “It will be like insurance that you can operate for several days,” Fischlin said.

Such sources of additional power will increasingly be needed as Switzerland moves away from nuclear power and as climate change alters precipitation amounts and patterns.

After four years of discussions with environmentalists, ending with an agreement, KWO has begun the permitting process. Construction could start by 2022 and be finished by 2030. By then, even less of the glacier will remain.

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