The Pacific Institute reported six years ago that China is the most dammed nation in the world, followed by the United States, India, Japan, Spain and Canada. These placements remain the same. Outside Magazine reports that 47,665 large dams exist in 140 countries and the weight of their water is so immense scientists believe it alters the speed of the earth's rotation. As noted in a previous column, dams provide one-fifth of the world's electricity and are also a mainstay in providing beneficial irrigation for one-sixth of the world's food supply. The downside is that 80 million people have been displaced by dams worldwide. Dams also inhibit fish migration and alter water flow in addition to adjusting temperatures. In recent years more than 212 dams have been torn down.