Lester R. Brown
Chapter 3. Rising Temperatures and Rising Seas: Reservoirs in the Sky
Snow and ice masses in mountains are nature’s freshwater reservoirs—nature’s way of storing water to feed rivers during the dry season. Now they are being threatened by the rise in temperature. Even a 1-degree rise in temperature in mountainous regions can markedly reduce the share of precipitation falling as snow and boost that coming down as rain. This in turn increases flooding during the rainy season and reduces the snowmelt that flows into rivers.
Beyond this, the glaciers that feed rivers during the dry season are melting. Some have disappeared entirely. Nowhere is the melting of glaciers of more concern than in Asia, where 1.3 billion people depend for their water supply on rivers originating in the Himalayan Mountains and the adjacent Tibet-Qinghai Plateau. 21
India ’s Gangotri Glacier, which supplies 70 percent of the water to the Ganges, is not only melting, it is doing so at an accelerated rate. If this melting continues to accelerate, the Gangotri’s life expectancy will be measured in decades and the Ganges will become a seasonal river, flowing only during the rainy season. For the 407 million Indians and Bangladeshis who live in the Ganges basin, this could be a life-threatening loss of water. 22
In China, which is even more dependent than India on river water for irrigation, the situation is particularly challenging. Chinese government data show the glaciers on the Tibet-Qinghai Plateau that feed both the Yellow and Yangtze Rivers are melting at 7 percent a year. The Yellow River, whose basin is home to 147 million people, could experience a large dry-season flow reduction. The Yangtze River, by far the larger of the two, is threatened by the disappearance of glaciers as well. The basin’s 369 million people rely heavily on rice from fields irrigated with Yangtze River water. 23
Yao Tandong, a leading Chinese glaciologist, predicts that two thirds of China’s glaciers could be gone by 2060. “The full-scale glacier shrinkage in the plateau region,” Yao says, “will eventually lead to an ecological catastrophe.” 24
Other Asian rivers that originate in this rooftop of the world include the Indus, with 178 million people in its basin in India and Pakistan; the Brahmaputra, which flows through Bangladesh; and the Mekong, which waters Cambodia, Laos, Thailand, and Viet Nam. 25
In Africa, Tanzania’s snow-capped Kilimanjaro may soon be snow- and ice-free. Ohio State University glaciologist Lonnie Thompson’s studies of Kilimanjaro show that Africa’s tallest mountain lost 33 percent of its ice field between 1989 and 2000. He projects that its snowcap could disappear entirely by 2015. Nearby Mount Kenya has lost 7 of its 18 glaciers. Local rivers fed by these glaciers are becoming seasonal rivers, generating conflict among the 2 million people who depend on them for water supplies during the dry season. 26
Bernard Francou, research director for the French government’s Institute of Research and Development, believes that 80 percent of South American glaciers will disappear within the next 15 years. For countries like Bolivia, Ecuador, and Peru, which rely on glaciers for water for household and irrigation use, this is not good news. 27
Peru , which stretches some 1,600 kilometers along the vast Andean mountain range and which is home to 70 percent of the earth’s tropical glaciers, is in trouble. Some 22 percent of its glacial endowment, which feeds the many Peruvian rivers that supply water to the cities in the semi-arid coastal regions, has disappeared. Lonnie Thompson reports that the Quelccaya Glacier in southern Peru, which was retreating by 6 meters per year in the 1960s, is now retreating by 60 meters annually. 28
Many of Peru’s farmers irrigate their wheat and potatoes with the river water from these disappearing glaciers. During the dry season, farmers are totally dependent on irrigation water. For Peru’s 28 million people, shrinking glaciers will eventually mean a shrinking food supply. 29
Lima , a city of 7 million people, gets most of its water from three rivers high in the Andes, rivers that are fed partly by glacial melt. While the glaciers are melting, the river flows are above normal, but once they are gone, the river flows will drop sharply, leaving Lima with severe water shortages. 30
In many agricultural regions, snow and ice masses are the leading source of irrigation and drinking water. In the southwestern United States, for instance, the Colorado River—the region’s primary source of irrigation water—depends on snowfields in the Rockies for much of its flow. California, in addition to depending heavily on the Colorado, also relies on snowmelt from the Sierra Nevada in the eastern part of the state. Both the Sierra Nevada and the coastal range supply irrigation water to California’s Central Valley, the world’s fruit and vegetable basket. 31
Preliminary results of an analysis of rising temperature effects on three major river systems in the western United States—the Columbia, the Sacramento, and the Colorado—indicate that the winter snow pack in the mountains feeding them will be dramatically reduced and that winter rainfall and flooding will increase. 32
With a business-as-usual energy policy, global climate models project a 70-percent reduction in the amount of snow pack for the western United States by mid-century. A detailed study of the Yakima River Valley, a vast fruit-growing region in Washington state, conducted by the U.S. Department of Energy’s Pacific Northwest National Laboratory shows progressively heavier harvest losses as the snow pack shrinks, reducing irrigation water flows. 33
Agriculture in the Central Asian countries of Afghanistan, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan depends heavily on snowmelt from the Hindu Kush, Pamir, and Tien Shan mountain ranges for irrigation water. Nearby Iran gets much of its water from the snowmelt in the 5,700-meter-high Alborz Mountains between Tehran and the Caspian Sea. 34
The snow and ice masses in the world’s leading mountain ranges and the water they store are taken for granted simply because they have been there since before agriculture began. Now that is changing. If we continue raising the earth’s temperature, we risk losing the reservoirs in the sky on which cities and farmers depend.
*Data and additional resources have been omitted from this mobile version of our website to ensure the most optimal experience. To view this page with its entire information, please visit the full website.