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Science-fiction-sounding rumor that China’s disrupted Earth’s rotation now can spread like crazy, but one should keep its sense of proportion in its place. NASA reports that China’s stunning Three Gorges Dam did slow down the rate at which Earth was spinning on its axis by mere minutes.
The Three Gorges Dam, the world’s largest hydroelectric power station, spans the Yangtze River in the Hubei province. The dam holds a staggering 39.3 billion cubic meters of water. According to NASA experts’ estimates, the weight and elevated level of the reservoir displaced Earth’s mass enough to add a paltry 0.06 microseconds to the day as the planet has slowed down in its rotation. As a bonus, the movement of mass shifted the axis of the Earth about 2 centimeters.
To put that in perspective, similar effects have been observed in the past. For instance, the 2004 earthquake in the Indian Ocean, which produced a deadly tsunami, actually accelerated the rotation of Earth, making the day shorter by about 2.68 microseconds. It’s tiny compared to the effect of the dam, but it’s measurable nonetheless.
The math used by NASA highlights the sheer size of grand projects’ capacity to influence planet physics. Keeping a vast quantity of water high up changes mass distribution on our planet. Due to rotation, it is influenced by mass and its distribution (such as the rotating ice-skating figure slowed when they flared their arms out). That the dam, which contains trillions of kilograms of water, has had any effect — one incredibly small effect, to be sure — surprises no one.
In addition to the physics, the Three Gorges Dam has also been criticized for its social and environmental expense. Over 1.2 million people were resettled during construction. Entire cities, villages, and ancient ruins were submerged. The dam has also been linked with increased landslides, altered ecosystems, and even local seismic shifts.
The rotation shift isn’t something that can be felt, and it is no imminent threat. But it is a reminder: human activity on Earth has that kind of impact to be quantified planet-wide. As countries pursue mega-projects in the name of development and energy, the larger impacts — and those outside the immediate boundaries — need to be examined and weighed.
