The world's dams hold so much water they've shifted Earth's poles

The construction of thousands of dams since 1835 has caused Earth's poles to wobble, new research suggests. Scientists found that large dams hold so much water, they redistribute mass around the globe, shifting the position of Earth's crust relative to the mantle, the planet's middle layer. Earth's mantle is gooey, and the crust forms a solid shell that can slide around on top of it. Weight on the crust that causes it to shift relative to the mantle also shifts the location of Earth's poles. "Any movement of mass within the Earth or on its surface changes the orientation of the rotation axis relative to the crust, a process termed true polar wander," researchers wrote in the journal Geophysical Research Letters.

- WORDS SASCHA PARE

Scientists already knew human activities that displace enormous volumes of water can trigger polar wander. A study published in March showed that dramatic ice melt due to climate change may move the poles by 27 metres by the end of this century. And a 2023 study concluded that groundwater extraction between 1993 and 2010 caused a polar drift of 80 centimetres. For the new study, researchers examined the impact of 6,862 dams, built across the planet, on Earth's poles between 1835 and 2011. The team used an already-published database of dams, which previously revealed that the volume of water held by these dams, a volume that could fill the Grand Canyon twice, had resulted in a 23-millimetre fall in global sea levels.