Spin cycle: Why Earth’s rotational speed is changing
Talk about making the world go round. At capacity, China’s Three Gorges Dam holds back 10 trillion gallons of water. (Shutterstock) Earth’s rotational speed is changing, and we’re more than partly responsible. A gigantic dam, our extraction of groundwater, melting ice sheets and rising sea levels are among the human-linked factors altering Earth’s spin. The thing all these factors have in common, is water. Where it stands, how it flows and where it settles has always shaped Earth’s rotation. During the last Ice Age, which ended about 20,000 years ago, for instance, the weight of the ice was so great that it depressed the surface of the planet. As it melted, large parts of the planet returned to their original form, leading to shifts in the orbit then too. Giant earthquakes have also traditionally altered Earth’s rotation, in tiny but still real ways. Anything that redistributes Earth’s mass can cause such a change. One of the things now estimated to do this is the world’s most powerful dam. China’s Three Gorges Dam across the Yangtze …
