Friday June 30, 2023
Scientific American —
The Earth has lost enough groundwater to thirsty humans to measurably tilt the planet’s axis of rotation.
The net water lost from underground reservoirs between 1993 and 2010 is estimated to be more than 2 trillion tons. That has caused the geographic North Pole to shift at a speed of 4.36 centimetres per year, researchers have calculated. The results appeared on 15 June in Geophysical Research Letters.
The tilt of the axis on which any celestial object spins tends to be stable. But small changes can occur when large masses shift location inside a planet and on its surface. “Every mass moving around on the surface of the Earth can change the rotation axis,” says Ki-Weon Seo, a geophysicist at Seoul National University.
Astronomers can track such motions in the Earth’s axis by observing quasars, the bright centres of distant galaxies that constitute practically immobile points of reference. The largest axis change is seasonal and is triggered by the motion of atmospheric masses as the weather and seasons change. This effect causes the Earth’s geographic poles to wobble by up to several metres every year.