Humans Built So Many Dams That Earth's Poles Got Shifted, Study Finds

New research has revealed that humans have built so many dams that the Earth's poles have shifted slightly. According to research, nearly 7,000 dams have been built globally, storing enough water to move the Earth's poles approximately 1 metre (3 feet) due to mass redistribution.

The storage of water in these dams has caused a 21-millimetre drop in global sea levels, which is significant as sea levels rose by 1.2 millimetres per year in the 20th century.

The phenomenon is known as true polar wander, where Earth's surface shifts over its inner magnetic north due to changes in mass distribution.

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"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," the researchers wrote in the study, published May 23 in the journal Geophysical Research Letters.

The researchers have analysed the impact of 6,862 dams, which were built across the planet, on Earth's poles between 1835 and 2011.

The North Pole shift didn't happen overnight. Between 1835 and 1954, the pole moved eastward towards Russia by 20 centimetres (8 inches) due to dam construction in Europe and North America.

On the other hand, the pole shifted westward towards North America by 57 centimetres (22 inches) due to dam construction in Asia and East Africa between 1954 and 2011.

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"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 redistributes mass in a different way around the world," study lead author Natasha Valencic, a graduate student in geology, geophysics and planetary science at Harvard University, said in a statement.

This shift has implications for sea level rise, and researchers need to consider water impoundment when calculating future sea level changes.

This phenomenon is an addition to the list of changes humans are causing to the Earth, including shrinking atmospheric layers, altering ocean circulation and activating volcanoes.

Valencic said that the impact of dams on sea levels is meaningful despite the fact that the location of the poles has relatively little impact on Earth's processes.

"We're not going to drop into a new ice age, because the pole moved by about a meter in total, but it does have implications for sea level," she said.