We think of dams as impressive, useful, often necessary works. They serve to contain water, produce energy, and protect territories from devastating floods. But we rarely stop to ask how profoundly these structures are changing the planet. The answer today is surprising: by building thousands of dams, human beings contributed to moving the North Pole.
This is not science fiction, nor an exaggeration. It is the result of a scientific study that tells, with numbers and data, how even actions that we consider “normal” can have global consequences.
Because accumulating water behind dams changes the balance of the planet
Dams have existed for thousands of years. Already in ancient Mesopotamia they were used for irrigation and flood control. Today, in addition to these functions, they produce hydroelectric energy and support entire economies. But there is a detail that remained in the background for a long time: each dam holds back enormous quantities of water, removing it from the oceans and concentrating it on the land.
The Earth, however, is not a rigid sphere. Its outer layer rests on partly fluid rocky material. This means that moving large masses – such as billions of tons of water – can change the balance of the planet, even influencing the orientation of the geographic poles.
This phenomenon is put in black and white by research published in Geophysical Research Letters, signed by a team of scientists from Harvard University. Analyzing the construction of around 7,000 dams between 1835 and 2011, the researchers calculated that the artificially trapped water was enough to cause an overall pole shift of around one metre.
To better understand the mechanism, scholars use a simple analogy: imagine a basketball spinning around. If you attach a clay ball to it, the ball will change its shape slightly to compensate for the new weight distribution. On Earth this process is known as true polar wanderor real polar drift.
The “trajectory” of the North Pole tells our story
One of the most fascinating aspects of the study is that the North Pole’s movement follows the map of global industrialization. Between 1835 and 1954, when most large dams were being built in North America and Europe, the North Pole moved about 20 centimeters toward the 103rd meridian east.
In the second half of the twentieth century, with the explosion of large hydraulic works in Asia and East Africa, the direction changed: the poles moved another 56 centimeters towards the 117th meridian west. A detail that tells us, better than many statistics, how global the human footprint is now.
Of all the possible examples, one stands out more than the others. The Three Gorges Dam, the largest in the world, is so massive that it has measurable effects on the Earth’s rotation. In 2005, NASA scientist Benjamin Fong Chao demonstrated that when the reservoir is completely full, this dam slows the Earth’s rotation by 0.06 microseconds.
We’re talking about an infinitesimal fraction of a second, of course. But it’s enough to make us realize that human infrastructure is not neutral, even on an astronomical scale.
Not just dams: groundwater consumption also shifts the poles
Dams are not the only factor at play. A 2023 study showed that groundwater pumping between 1993 and 2010 caused a net loss of about 2 trillion tons of water, contributing to a pole shift of more than 4 centimeters per year.
The good news is that we are not at risk of turning the Earth into Uranus, which rotates almost on its side. But, as the researchers explain, even minimal variations have concrete effects on sea levels and the global climate balance.
Ultimately, this story leaves us with an uncomfortable but necessary question: If we’ve managed to shift the poles without even realizing it, how much more of the planet are we changing every day?
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