China has started building what is expected to be the largest hydropower complex yet, and it is already stirring debates that stretch far beyond the Himalayas.
The Medog Hydropower Station in Tibet will harness the power of the Yarlung Tsangpo River and is designed to generate about 300 billion kilowatt hours of electricity every year, roughly triple the output of the existing Three Gorges Dam on the Yangtze River.
So what does a dam in a remote gorge have to do with the length of your day.
Approved by Beijing in late 2024 and launched in July 2025
Approved by Beijing in late 2024 and launched in July 2025, the project carries an estimated cost of at least 170 billion dollars and an installed capacity of 60 gigawatts. It will tap a 2,000 meter drop in the river over about 50 kilometers near Medog County in the Tibet Autonomous Region using five cascade power stations.
Premier Li Qiang has called it a “project of the century” and stressed the need to protect the environment during construction.
Scientists already know that mega dams can leave measurable fingerprints on Earth’s rotation
Scientists already know that mega dams can leave measurable fingerprints on Earth’s rotation.
Researchers at NASA found that filling the reservoir behind the Three Gorges Dam shifted Earth’s axis by about two centimeters and lengthened the day by roughly 0.06 microseconds, a delay far too small to notice when you glance at a clock yet large enough for satellites and geophysical instruments to detect.
New work led by a team at Harvard University shows that Medog will join a much larger story
New work led by a team at Harvard University shows that Medog will join a much larger story. In a study in the journal Geophysical Research Letters, summarized by the American Geophysical Union (AGU), researchers analyzed 6,862 dams worldwide and concluded that the mass of water stored behind them nudged the geographic North Pole by about 3.7 feet, a phenomenon known as true polar wander.
The effect will not change everyday life, yet it confirms that reshaping rivers can subtly rebalance the planet, much like shifting your weight on a spinning chair.
In that context, a single new dam, even one on this scale, will not suddenly tip Earth off its axis
In that context, a single new dam, even one on this scale, will not suddenly tip Earth off its axis. For the most part, its rotational effect will be tiny compared with the combined influence of existing reservoirs.
The more immediate stakes are about energy and climate, since 300 billion kilowatt hours of hydropower is roughly equal to a year’s electricity use in Britain and could displace significant coal fired generation inside China.
Supporters in China point to those benefits for homes, factories, and the air conditioners that keep people cool through sticky summer heat
Supporters in China point to those benefits for homes, factories, and the air conditioners that keep people cool through sticky summer heat. Critics inside and outside the country focus on a different set of numbers, the biodiversity of the Yarlung Tsangpo canyon, the fact that the site lies in a seismically active zone, and the millions of people downstream in India and Bangladesh who depend on the Brahmaputra River basin for farming, fishing, and drinking water.
Chinese officials describe Medog as a run of the river project meant to limit storage and have said it will not significantly affect flows, but detailed environmental assessments and hydrological data have not been fully shared with neighbors, feeding regional water security worries.
At the end of the day, Medog captures the paradox of building out clean energy at planetary scale
At the end of the day, Medog captures the paradox of building out clean energy at planetary scale.
Hydropower can deliver huge amounts of low carbon electricity without the fuel costs that show up on a household electric bill, yet mega dams reshape landscapes, displace communities, and, as current research suggests, even leave faint marks on the way Earth spins.
The press release was published on AGU.
