For almost two centuries, human ingenuity has shaped the landscapes of the planet, in particular through the massive construction of dams intended to retain water for irrigation, energy production, or even supply of drinking water. However, these gigantic hydraulic works, beyond their economic and social role, had an unsuspected impact on the earth itself: they modified the position of the earth’s poles. A recent discovery resulting from a study published in Geophysical Research
Letters reveals how the redistribution of water through the globe causes a slight but real displacement of the axis of rotation of our planet.
A mass of water that makes the earth move
The phenomenon at the origin of this polar drift lies in the redistribution of the masses on the surface of the earth. Indeed, the planet is made up of several layers, including the solid crust on which we live, resting on a viscous and malleable coat. When a large amount of water is retained by a dam, it exerts considerable pressure on the earthly crust, locally modifying the distribution of the masses. This new distribution then leads to a slight sliding of the crust with respect to the mantle, which results in a modification of the position of the poles.
This process is called the “true polar drift”: it is a displacement of the axis of rotation of the earth compared to its surface. Although this movement is relatively low on a human scale, it remains measurable and has important implications for geophysics, navigation and understanding of the climate.
An unsuspected movement since 1835
Scientists already knew that human activities can influence polar drift. For example, previous studies have shown that massive underground water extraction or the accelerated melting of polar ice due to climate change help move the axis of the earth. However, the new study has focused on an often overlooked factor: the impact of dams built around the world.
Between 1835 and 2011, more than 6,800 dams were erected at different times and in various regions. These infrastructures have made it possible to retain a volume of water so large that it could twice fill the Grand Canyon. By accumulating this water far from the oceans, these dams not only lowered the world level of the sea by around 23 millimeters, but also helped to move the position of the poles of approximately 1.1 meters.
This polar drift took place in two distinct phases, depending on the regions where the dams were built. The first phase, from 1835 to 1954, was linked to the rise of dams in North America and Europe. This phenomenon moved the North Pole about 20 centimeters to the 103rd meridian is, an imaginary line crossing Russia and Mongolia.
The second phase, from 1954 to 2011, corresponds to strong growth in dams in East Africa and Asia. This new mass of distributed water has led to a more marked displacement, 57 centimeters, this time around the 117th western meridian, which crosses the west of North America and the South Pacific. These movements do not follow a linear trajectory, but form a kind of unstable zigzag around the previous position.
Image credit: Valencic et al. (2025)
A modest but significant impact
At first glance, a movement of a meter of the poles over almost two centuries may seem minimal. And it is true that this movement does not threaten the stability of the planet or the short -term global climatic conditions. However, the fact remains that it must be taken into account in several scientific and technical areas.
For example, GPS navigation systems, geodetic surveys and climatic models are based on precise knowledge of the position of the poles. A shift, even weak, can therefore lead to errors in these areas, which underlines the importance of understanding and modeling these movements.
In addition, the impact of dams on sea level is particularly crucial. The drop of almost 2.3 centimeters due to the water holder in these infrastructures represents approximately a quarter of the overall increase in the ocean level observed in the 20th century, which amounts to 12-17 centimeters. In other words, without these dams, the level of the seas would have increased even more, with even more marked consequences for coastal areas and vulnerable populations.
Towards better integration of human factors in climate models
This study therefore invites the scientific community to further integrate the impact of dams into its projections on the future evolution of terrestrial poles and the level of the oceans. Because continuous construction of new hydraulic infrastructure, especially in regions such as Asia and Africa, could still modify the distribution of water on earth, accentuating these phenomena.
Beyond scientific implications, this discovery illustrates how much human activity deeply and permanently influences our planet, even in mechanisms as fundamental as the rotation of the earth. This is a striking example of the interconnection between our technological choices and the natural balance of the earth, which deserves to be better understood to anticipate the future environmental challenges.
