Overview
- NASA geophysicist Benjamin Fong Chao’s calculations, reported across outlets this week, estimate that filling the Three Gorges reservoir redistributes mass enough to nudge Earth’s rotation and shift the axis slightly.
- The effect arises from a change in Earth’s moment of inertia when roughly 40 cubic kilometres of water are held in the Yangtze reservoir; that physics is like a skater changing spin by moving their arms.
- The modeled lengthening of the day is about 0.06 microseconds, a scientifically measurable amount that is millions of times smaller than changes caused by major earthquakes or tsunamis.
- Practically, the change is imperceptible for daily life and timekeeping, but the finding highlights that planned hydropower builds such as the Medog projects could add to cumulative mass-redistribution effects by 2035.
- Scientists say the result matters for precise Earth geodesy and long-term monitoring because human engineering now joins natural forces as a small but detectable driver of Earth’s rotational dynamics.