The glaciers that have long provided water and electricity to this part of Bolivia are melting and disappearing, victims of global warming, most scientists say.If the water problems are not solved, El Alto, a poor sister city of La Paz, could perhaps be the first large urban casualty of climate change. A World Bank report concluded last year that climate change would eliminate many glaciers in the Andes within 20 years, threatening the existence of nearly 100 million people.