People living in arid climates near mountains usually rely on glacial melt for their water for part of the year. Though rivers are fed largely by snowmelt, in late summer, a significant part of river flow comes from melting glaciers according to the National Snow and Ice Data Center.
In recent decades, global climate change has had a huge impact on high mountain environments. Snow, glaciers and permafrost are especially sensitive to changes in the atmosphere because of their proximity to warming conditions. The impacts of glacier retreat are one of the most visible signs of climate change as can be seen below.
The Waggonwaybreen glacier in Svalbard, Norway, has retreated substantially since 1900. “The rate of change that we see in the moment, recorded most directly and visibly by mountain glaciers, is way, way, way faster than it was at the end of the ice age. What we have seen over the last 150 years, all over the planet, is that these mountain glaciers record a retreat corresponding to 1˚ to 1.5˚C warming over 150 years, with the biggest part of that retreat happening over the last decade. The speed with which these glaciers are retreating has exponentially speeded up…and if you compare the rate of change, nothing ever happened like that in the geological past.” Joerg Schaefer, a research professor at Lamont-Doherty Earth ObservatoryScott K Johnson of ars Technica writes
The first study, by Matthias Huss and Regine Hock, looks at the effect shrinking glaciers have on local water supplies. Glaciers help sustain rivers downslope through the drier months by providing a constant stream of meltwater, like a frozen water tower that collects in the winter and rations it out over the summer.
For a while, a shrinking glacier will contribute even more meltwater runoff to the river, but there comes a point when a smaller glacier can't keep up. Once it produces less meltwater, it’s downhill to “peak runoff” from there. This process has already been observed at a number of glaciers, but a global picture had not yet been painted.
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The really shocking number, however, is the number that have already passed “peak runoff” before the present day. That was true for 45 percent of the glacier-fed watersheds in the model. For these rivers, the summer glacier-water contribution is already decreasing.
In the middle emissions scenario, over 90 percent of glaciers cross that point by the end of the century. For half of the watersheds, the reduced meltwater means a decrease of summer streamflow under five percent, but a third of them lose more than 10 percent. There’s also a shift in timing. Generally, the supply of early-summer meltwater increases as warmer temperatures get glaciers melting sooner than they used to. The big decline comes later in the summer, which is often the time of year that reliable streamflow is needed the most.
Reness Cho of Columbia University writes a fascinating piece for State of the Planet.
“But we know things are going in one direction and will be getting much faster in this direction. There will be more warming and more melt. All the things that could slow the melting down, like the cooling of the Arctic or more accumulation of snow in summer, are not going to happen. And even if they did, they would be short, just a bump in the road.”
Here are a few examples of the glaciers we are losing.
Montana’s Glacier National Park had 150 glaciers in 1850; today there are 25. The greater Himalayas, which contain nearly one-third of Earth’s non-polar ice, have warmed much more than the global average over the last 100 years; between 1950 and 2000, 82 percent of glaciers in western China shrank. The Aletsch Glacier, the largest in Switzerland, retreated 1.7 miles between 1880 and 2009. By 2000, the Furtwangler Glacier on top of Mount Kilimanjaro in Tanzania was half the size it was in 1976If the melting continues over the next few decades, some of the world’s most populous areas could run out of water during the dry season. For awhile, the increase in flow from melting ice and snow during the dry season will seem like a boon, but in the future, the downstream flow’s variability will increase and eventually flow could disappear altogether, impacting food production, biodiversity and economic growth.
When 247 million cubic feet of snow and ice collapsed off a glacier in the dry, mountainous region of western Tibet in 2016, the roiling mass took with it nine human lives and hundreds of animals, spreading more than five miles in three minutes at speeds of nearly 200 miles per hour. The event surprised scientists, who had seen a collapse that big and that fast only once before. And then it happened again, three months later, on a neighboring glacier, though without fatalities. Glaciologists hadn’t quite believed that glaciers could behave this way, and suddenly they had witnessed two similar collapses in a year. An analysis of the events, published this week in the journal Nature Geoscience, found that climate change was the culprit in both collapses. The study suggests that in addition to the known risks posed by a warming climate, such as sea level rise, we may also be in line for some cataclysmic surprises. Kendra Pierre-Lewis/NY TimesSchaefer noted that this information is critical for political and social scientists to prepare for the inevitable loss of meltwater for those dependent on alpine glaciers for their water. "We need the five- to 10-year perspective—that is our mission here at Lamont-Doherty, to preach that to everybody."
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