Part 4: Shrinking Glaciers
You will hear part of a lecture on mountain environments about the loss of glacier ice.
Lời thoại bài nghe (transcript)
Lecturer: Good morning, everyone. In today's lecture in our series on mountain environments, I'm going to look at what is happening to the world's glaciers, how we know it's happening, and what some mountain communities are doing in response.
Lecturer: Let's start with monitoring. How do scientists actually measure the loss of ice? The oldest method is surprisingly simple. Researchers drill long metal stakes into the surface of the glacier, and when they return, they measure how much of each stake has been exposed. I said in the handout that this is done once a year, but in fact most teams take readings twice a year, at the end of winter and again at the end of summer, so they can separate the snow that's gained from the ice that's lost.
Lecturer: For a longer view, we rely on historical records. Some people imagine that old paintings are useful here, and occasionally they are, but artists weren't always accurate. Far more reliable are the photographs taken by early climbers and surveyors, some of them more than a hundred years old. By standing in exactly the same spot today and taking a new picture, researchers can show very clearly how far a glacier has retreated.
Lecturer: The most important tool now, though, is the satellite. Satellites can't easily tell us how thick a glacier is, but they can measure very small changes in the height of the ice surface, year after year, across entire mountain ranges. That allows us to calculate the total volume that has been lost.
Lecturer: So what are the effects? The most immediate one concerns water. In many mountain regions, glaciers act like a natural reservoir. They store water as ice during the cold months and release it slowly in the hottest, driest part of the year, exactly when farmers downstream need it most for irrigation. Now, here's the paradox. When a glacier first starts to shrink rapidly, rivers actually carry more water than before, because more ice is melting. Communities may even believe that the situation is improving. But once the glacier becomes small enough, the flow begins to fall, and eventually there is a serious shortage of water in the dry season.
Lecturer: A second effect is a hazard. As glaciers retreat, meltwater often collects in lakes at the foot of the ice. These lakes are frequently held back by natural walls of loose rock and debris left behind by the glacier itself. Those walls are unstable, and if one collapses, perhaps after an earthquake or a landslide, the lake can empty in a matter of hours, sending a flood down the valley.
Lecturer: There's also a feedback effect. Clean ice and snow reflect most of the sunlight that falls on them. When the ice melts and dark rock is exposed, that rock absorbs much more heat, which warms the surrounding area and speeds up the melting of the ice that remains.
Lecturer: Finally, let's turn to responses. Some of these are local and, frankly, quite small in scale. At several ski resorts, for example, managers now cover parts of the glacier during the summer months with large sheets of white fabric. This reflects sunlight and can reduce melting in those areas by more than half. It's expensive, though, and it only protects a tiny fraction of the ice.
Lecturer: In some dry mountain regions, villagers have found a cheaper solution. In winter, they divert stream water and allow it to freeze in shaded valleys, where the sun doesn't reach for much of the day. These artificial glaciers, as they're called, then melt gradually in spring, just when the young crops need water and before the natural meltwater arrives.
Lecturer: These are clever adaptations, and they matter a great deal to the people who use them. But I want to be clear that they treat the symptoms, not the cause. Glaciers will only stabilise in the long term if there are large reductions in global emissions. In next week's lecture, we'll look at what that might mean for mountain tourism.
