Big dams may have changed how the Earth rotates, new study finds
Human engineering appears to have moved the planet, literally. According to new research published this month, the global boom in dam construction over the past two centuries has caused measurable shifts in Earth’s poles. The data shows that it has even led to a small but significant drop in sea levels.
To truly understand how it has affected our planet, we first have to look at how the Earth’s outer crust works. The crust floats on what is essentially a layer of molten rock, which means that the it can move when mass shifts around the planet’s surface. Scientists call this wobbling true polar wander.
While this phenomenon does happen naturally -- such as when glaciers grow or melt -- researchers have now shown that human-made dams also shift the Earth's poles. A better way to think about it is to imagine that you stick a lump of clay on a basketball as it spins. As the ball moves, it slowly adjusts to account for the new weight. On Earth, the outer crust works similarly, realigning itself and our geographic poles, resulting in a slower drift for the planet.
This new study looked at data from over 6,862 dams built between 1835 and 2011. Together, these dams store enough water to fill the Grand Canyon twice, the researchers note. And that trapped water isn’t just sitting there, having no effect on our world. Not only did these dams remove volume from the oceans (dropping global sea levels by about 21 millimeters) but the filling of these dams also shifted mass on land, causing the Earth's poles to move by roughly 1.1 meters (3.7 feet).
The researchers identified two major phases of dam construction that shifted Earth's poles in the past. From the 1800s to mid-1900s, dam building in North America and Europe pulled the North Pole slightly toward Asia. However, from the 1950s onward, large dams in Africa and Asia shifted the pole back toward western North America. While these shifts in Earth’s poles are small on a global scale, they matter quite a bit to understanding our planet and its various systems.
For starters, the redistribution of water greatly affects how scientists model sea level rise. During the 20th century, sea levels rose an average of 1.2 millimeters per year -- but about a quarter of that was offset by dams holding water on land. Even more important, though, is the fact that wherever water is stored can change the pattern of sea level rise. Some regions may see higher or lower increases in the sea level depending on dam placement.
This research is just one part of a growing list of evidence that human actions are completely reshaping Earth in massive ways. As climate change drives further glacier melt and sea level rise, tracking how mass moves across the planet will be crucial to understanding not just our oceans, but ongoing shifts in Earth’s poles. Especially those caused by human intervention.
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