Here’s what you’ll learn when you read this story:
Humanity’s impact on the planet is so immense that our engineered megastructures have altered the very rotation of the planet.
A new study from Harvard University analyzes how dam building—primarily the two stages that spanned from 1835 to 2011—has caused the Earth’s poles to move roughly three feet.
In addition to changing the Earth’s rotation, dams have caused a global decrease in water levels.
Dams have long been one of humanity’s greatest tools for controlling the world’s water. The very first dams, constructed in ancient Mesopotamia, were used for many of the same purposes as they are today: water irrigation and flood control (though, a few centuries later, we now also use them to generate hydropower). But as the era of big dams truly got underway in the 19th and 20th centuries, we’ve also begun to learn about the unintended consequences of these dams. They drastically disturb natural ecosystems, negatively impact water quality, and exacerbate soil erosion—oh, and they’ve also altered the location of the Earth’s poles.
In a new study published in the journal Geophysical Research Letters, a team of scientists at Harvard University details their discovery that the rampant construction of dams from 1835 to 2011 has locked up so much water that the Earth’s poles have moved slightly from their axial rotation. Because Earth’s outermost layer rests upon another layer of liquid rock, a redistribution of mass on the surface—whether accomplished by glaciers during an ice age or by locking up water behind dams—it can influence the orientation of the Earth’s poles. The authors describe the phenomenon like slapping a lump of clay on a basketball and spinning it. In an effort to maintain momentum, the ball adorned with clay will shift slightly toward the equator, which eventually impacts the poles in a process known as “true polar wander.”
Thankfully, Earth is not destined to end up like the planet Uranus, forever spinning on its side. Two centuries of frantic dam-building (about 7,000 of them in total) has only nudged the poles about three feet and caused a 0.83-inch drop in global sea levels.
“As we trap water behind dams, not only does it remove water from the oceans, thus leading to a global sea level fall, it also distributes mass in a different way around the world,” Harvard University graduate student Natasha Valencic, the lead author of the study, said in a press statement. “We’re not going to drop into a new ice age, because the pole moved by about a meter [or about three feet] in total, but it does have implications for sea level.”
Interestingly, the movement of the poles also matches the history of industrialization. Between 1835 and 1954, a majority of dams were constructed in North America and Europe, moving the North Pole 8 inches to the 103rd meridian east. Once East Africa and Asia began constructing dams in the latter half of the 20th century, the poles moved once again—this time 22 inches toward the 117th meridian west, according to the authors.
The most eye-popping example of dams’ astronomical impact can be seen by analyzing the effects of China’s Three Gorges Dam, the largest dam in the world. In 2005, NASA scientist Benjamin Fong Chao showed that when full, this mega-dam alone slowed the rotation of the Earth by 0.06 microseconds, or 60 billionths of a second.
Dams aren’t the only anthropomorphic force at work impacting the orientation of the Earth’s poles, however. A 2023 study analyzed the impact of pumping groundwater from reservoirs, and estimated that between 1993 and 2010, net water loss amounted to roughly 2 trillion tons and caused a 4.36 centimeter shift every year.
Humanity continues to impact our planet in a myriad of complex ways. Hopefully, the more we learn about these impacts, the more we can mitigate any negative impacts they may bring along with them.
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