Humans have tilted the Earth
Meltwater from icebergs shifts Earth's axis of rotation – but new evidence shows that groundwater pumping does so too, and could one day influence the climate.
It is well-documented that Earth’s axis of rotation and tilt – responsible for the changing seasons on our planet – change over time.
But an international research team headed by Seoul National University in South Korea has concluded that since humans began pumping water from the ground to use for cooking and irrigating fields, Earth’s tilt has shifted more significantly than would be expected.
They reached this conclusion after analysing data on the movement of water masses on Earth and our planet’s axis of rotation between 1993 and 2010. The team observed that the tilt has shifted almost 80cm, something that could affect the Earth’s climate in the long term, they believe.
If you imagine Earth as a top which is spinning around itself, the invisible axis of rotation will move back and forth as the water masses move to different places on Earth. Scientists have known about this phenomenon only since 2016, so it is still a relatively new area of research. For many years it was presumed that the melting of ice masses was the primary cause of water movement on Earth.
So the researchers behind the new discovery started by investigating the relationship between changes of the axis of rotation and the movement of water caused by the melting of ice caps and glaciers. But the results from their models didn’t match the relationship between the two quantities.
So they decided to include groundwater pumping as well. Previous climate models have demonstrated that between 1993 and 2010, people pumped up some 2150 gigatonnes of groundwater, causing a global sea level rise of 6.24mm during the period.
By adding groundwater pumping to the models for ice melting, the relationship between the distribution of the water masses and the shift of the rotational axis was found to match.
In fact, the researchers observed that Earth's geographic North Pole moved roughly eastwards at an average speed of 4.36cm a year between those years, a total shift in the axis of rotation of 78.5cm.
“I am very happy to find the unexplained cause of the drift of the pole of rotation,” said Ki-Weon Seo, one of the researchers behind the study. “On the other hand, as a resident of Earth, and a father, I am concerned and surprised to see that groundwater pumping is another source of sea level rise.”
The actual impact of this humaninduced shift is not yet known, but it could affect temperatures and sea-level rise in the long term. Key reasons for the pumping of groundwater include agriculture, drinking water, industrial processes, and to combat drought.