The 21st Century climate challenge

2Climate shocks: risk and vulnerability in an unequal worldThe past 25 years have seensome glacier systems in thetropics transformed. Theirimpending disappearancehas potentially disastrousimplications foreconomic growth andhuman developmentthe lifeblood of vast ecological and agriculturalsystems.Himalayas is a Sanskrit word thattranslates as ‘abode of snow’. Today the glacialabode, the largest mass of ice outside of thepolar caps, is shrinking at a rate of 10–15metres a year. 73 The evidence shows the paceof melting to be uneven. But the direction ofchange is clear.At current rates two-thirds of China’sglaciers—including Tien Shan—will disappearby 2060, with total melting by 2100. 74 TheGangotri glacier, one of the main waterreservoirs for the 500 million people living inthe Ganges basin, is shrinking by 23 metresa year. One recent study by the Indian SpaceResearch Organisation, using satellite imagesand covering 466 glaciers, found a 20 percentreduction in size. Glaciers on the Qinghai–Tibetplateau, a barometer of world climate conditionsand the source of the Yellow and Yangtze rivers,have been melting by 7 percent a year. 75 Withany climate change scenario in excess of the 2°Cdangerous climate change threshold, the rate ofglacial retreat will accelerate.Accelerated glacial melt creates some immediatehuman development risks. Avalanches andfloods pose special risks to densely populatedmountain regions. One of the countries facingsevere risks today is Nepal, where glaciers areretreating at a rate of several metres each year.Lakes formed by melting glacier waters areexpanding at an alarming rate—the Tsho RolpaLake being a case in point, having increasedmore than sevenfold in the last 50 years. Acomprehensive assessment completed in 2001identified 20 glacial lakes that could potentiallyburst their banks, with catastrophic consequencesfor people, agriculture and hydropowerinfrastructure, unless urgent action is taken. 76As glacial water banks are run down, waterflows will diminish. Seven of Asia’s great riversystems—the Brahmaputra, the Ganges, theHuang He, the Indus, the Mekong, the Salweenand the Yangtze—will be affected. These riversystems provide water and sustain food suppliesfor over 2 billion people. 77• The flow of the Indus, which receives nearly90 percent of its water from upper mountaincatchments, could decline by as much as 70percent by 2080.• The Ganges could lose two-thirds ofits July–September flow, causing watershortages for over 500 million people andone-third of India’s irrigated land area.• Projections for the Brahmaputra point toreduced flows of between 14 and 20 percentby 2050.• In Central Asia, losses of glacial melt intothe Amu Darya and Syr Darya rivers couldrestrict the flow of water for irrigation intoUzbekistan and Kazakhstan, and compromiseplans to develop hydroelectric powerin Kyrgyzstan.Climate change scenarios for glacial meltingwill interact with already severe ecologicalproblems and put pressure on water resources.In India, competition between industry andagriculture is creating tensions over the allocationof water between states. Reduced glacial flowswill intensify those tensions. Northern Chinais already one of the world’s most water-stressedregions. In parts of the Huai, Hai and Huang(Yellow) basins (the ‘3-H’ river basins) currentwater extraction is 140 percent of renewablesupply—a fact that explains the rapid shrinkageof major river systems and falling groundwatertables. Over the medium term, changed glacialmelting patterns will add to that stress. In an areathat is home to around half of China’s 128 millionrural poor, contains about 40 percent of thecountry’s agricultural land area and accounts forone-third of GDP, this has serious implicationsfor human development (box 2.8). 78Tropical glaciers are also shrinkingTropical glaciers are retreating even more rapidlythan those in the Himalayas. In the lifetime ofa glacier, a quarter of a century represents theblink of an eye. But the past 25 years have seensome glacier systems in the tropics transformed.Their impending disappearance has potentiallydisastrous implications for economic growthand human development.Surveys by geologists suggest that therate at which Latin America’s glaciers areretreating is increasing. There are 2,500square kilometres of glaciers in the tropical96 HUMAN DEVELOPMENT REPORT 2007/2008