If you’ve ever worked as a waitress, you’ll know how easily a tray becomes unbalanced when drinks are moved around.
It turns out, Earth has the same problem.
Humans have pumped so much water out of the ground and redistributed it on the surface that the planet has tilted on its axis.
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Previous estimates have suggested more than 2,150 gigatons of groundwater was extracted between 1993 and 2010, equivalent to more than 6 millimetres of sea level rise.
However, scientists had difficulty confirming those figures – until now.
The Earth’s rotational pole – the point around which it spins, as opposed to its magnetic pole – migrates regularly, but a recent shift of almost 80 centimetres couldn’t be explained by the movement of ice sheets and glaciers alone. The calculations were off by 78.5cm.
But by adding the groundwater estimates, the modelling matched the movement – proving that extracting subterranean water not only shifted the Earth’s axis, but is a major source of sea level rise.
‘Earth’s rotational pole actually changes a lot,’ said lead author Dr Ki-Weon Seo, a geophysicist at Seoul National University.
‘Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.’
The study showed Earth’s axis is tilting by 4.3cm a year.
‘I’m very glad to find the unexplained cause of the rotation pole drift,’ said Dr Seo.
‘On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea level rise.’
Between the years studied, the largest volume of water was redistributed in North America and northwestern India. Both are found at midlatitudes, which have a greater impact on the rotational pole.
‘Observing changes in Earth’s rotational pole is useful for understanding continent-scale water storage variations,’ said Dr Seo.
‘Polar motion data are available from as early as the 19th century, so we can potentially use those data to understand continental water storage variations during the last 100 years.’
The study is published in Geophysical Research Letters.
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