One giant dam has already nudged the way our planet turns. When the enormous Three Gorges Dam reservoir in China filled with tens of billions of tons of water, NASA calculations showed that the extra mass made each day about 0.06 microseconds longer and shifted Earth’s rotation axis by roughly 2 centimeters.⁠ Now, Beijing is moving ahead with an even more ambitious project on the Tibetan Plateau. A new hydropower complex planned for Medog County in Tibet is expected to become the largest dam system on the planet, with an annual output roughly three times that of Three Gorges and a price tag of around 1.2 trillion yuan.⁠ ⁠ Chinese Premier Li Qiang has already described it as a “project of the century” that could reshape global clean energy supply.⁠ ⁠ _____⁠ ⁠ In 2005, scientists at NASA's Jet Propulsion Laboratory modeled what would happen if the Three Gorges reservoir reached full capacity. Their conclusion was striking even if the numbers were small. The stored water would lengthen th...