Austin American-Statesman: To some observers, the Three Gorges Dam shows how the United States and China could cooperate to slow global warming. When the dam’s reservoir reaches its maximum height this fall, 26 huge turbines will produce enough electricity to power most of Shanghai, China’s largest city, without releasing any gases that contribute to climate change. To others, however, the Yangtze River dam — the world’s largest at five times the width of America’s Hoover Dam — highlights the difficulties …