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Chacaltaya Glacier, Bolivia Top Impact Other Impacts
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The fast-growing Bolivian metropolis of El Alto-La Paz depends on Andean glaciers for its water supply. One such glacier, Chacaltaya, disappeared in 2009, and other Bolivian glaciers are shrinking. Lack of access to water has already sparked citizen protests, as seen here in the streets of El Alto.1 |
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Key Facts As glacial retreat reaches critical levels in Bolivia, water stress plagues the cities of El Alto and La Paz.3,8,9 If our heat-trapping emissions continue to rise at current rates, many tropical glaciers in Latin America are likely to disappear within a few decades.12
Details La Paz and the neighboring city of El Alto, Bolivia, compose one of the fastest-growing urban areas in Latin America.2,3 La Paz, the world's highest capital city, depends on runoff from Andean glaciers for around 30 percent of its water supply.2,4 According to estimates by the United Nations Children's Fund (UNICEF), only about one-third of El Alto residents had access to all water-related services in the late 1990s, and one in five lacked potable water.5,6 With the basic needs of so many people already unmet, residents revolted against privatization of the city's water system, which priced tens of thousands of people out of access to water. In 2005 the government returned El Alto's water system to public control.7 However, water shortages continue to plague El Alto-La Paz, as glacial retreat reaches critical levels in Bolivia.8,9 Chacaltaya glacier—some 12 miles (20 kilometers) northeast of La Paz—lost more than 60 percent of its volume from the 1940s to the early 1980s, and more than 90 percent by the late 1990s.9,10 Early this century, scientists projected that Chacaltaya glacier would melt completely by 2010,9 and it disappeared in 2009.3,11 The Zongo glacier northeast of Chacaltaya is also shrinking.10 Glaciers across South America have shrunk severely in recent decades, with many vanishing altogether.12 Scientists attribute the accelerating retreat of Andean glaciers to climate change—primarily warming temperatures, higher humidity, and shifting precipitation.13 Average temperatures throughout the tropical Andes have been rising since the mid-twentieth century, with the rate of increase jumping to around 0.6° F (0.33° C) per decade in the last quarter of the century.13,14 High humidity also plays a role in shrinking the Andean glaciers, as it causes the glaciers to melt rather than turn into vapor through a process known as sublimation. Melting decreases the surface reflectivity—or albedo—of a glacier, which means that it absorbs more of the sun's energy. That leads to a cycle of further warming and melting.9 Scientists have also linked the disappearance of the Chacaltaya glacier to decreases in precipitation linked to more frequent El Niño events.9 The El Niño-Southern Oscillation (ENSO) is a cyclical shift in ocean temperatures and atmospheric pressure in the Pacific Ocean. In a warming world, El Niño phases have been lasting longer and become more intense.9,15 Part of a Larger PatternBy storing water as ice, glaciers provide a long-term source of water during droughts.16 Glacial ice covers one-tenth of Earth's surface, and accounts for about three-quarters of the world's freshwater.17 The ice sheets of Greenland and Antarctica hold all but 3-4 percent of the world's glacial ice. Of the remaining amount, South America has only 5 percent.18 Glacial melting provides some of the clearest evidence of global warming.17 Temperatures rising by as little as 0.2° F (0.1° C) per decade can cause glaciers to shrink by hundreds or even thousands of yards (meters) in length.17 Glaciers around the world have been retreating over the past century.19 Although some have been growing, the overall rate of retreat has risen in the past decade, and the total volume of glaciers on Earth is rapidly declining.17,19,20,21 Scientists estimate that the average annual melting of mountain glaciers has doubled since 2000—on top of the already higher melting rates of the last two decades of the twentieth century. The year 2006 set a new record for loss of mass among monitored glaciers.17 What the Future HoldsScientists project that South America is likely to warm by 3.2-8.1° F (1.8-4.5° C) by the end of this century, with the scope of climate change depending on the choices regarding emissions we make today.12 If our heat-trapping emissions continue to rise at current rates, many tropical glaciers in Latin America are likely to disappear within a few decades.12 The melting of the tropical Andean glaciers endangers the water supply of tens of millions of Bolivian citizens, as well as countless plant and animal species that inhabit the area.4 The loss of glaciers as a natural means of managing water resources could harm mountain communities, cities, local wildlife, and agriculture.22 It could also disrupt hydropower,4,23 which accounts for half of Bolivia's electricity supply.4 Fortunately, Bolivia is among a handful of countries that are actively trying to adapt to glacial retreat. The government is exploring approaches such as diversifying water sources, managing demand for water and collection of rainfall, and improving the efficiency of agricultural water use.5 Endnotes
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Global Warming Effects Around the World
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