The Human Effect: Rampant Groundwater Extraction Caused Earth’s Axis to Tilt Further

Scientists have detected a measurable tilt in the Earth’s axis of rotation due to an anthropogenic factor, and that is extraction of groundwater. A research published in the journal Geophysical Research Letters on June 15 has reported about it. The researchers claimed that during the period of 1993-2010, the net water extracted from underground reservoirs was about 2,150 giga tonnes, which resulted in the North Pole shifting nearly 80 centimetres east.

To understand more about the phenomenon, imagine a filled ball that rotates on a fixed axis making an angle with it. Now, if some material from it is taken out, what will be observed? The ball starts tilting toward the direction where the material was taken out from. The axis that the ball rotates on will also wobble, shifting toward the direction the mass was taken out from. This happens because the internal distribution of masses in the ball changes. This idea is also applicable to rotating planetary objects like the Earth.

Scientists can detect such planetary wobbles. Notably, the change of Earth’s axis is a natural phenomenon, which is mainly caused by natural forces, such as motion of ocean currents or by motion of atmospheric masses with the change of the seasons etc. This causes Earth’s poles to shift by several metres every year. Shift in the distribution of the mass of water also causes a shift in the rotational axis of Earth, including a change in the groundwater level.

The amount of water extracted from the ground during the study period (1993-2010) is equivalent to water that would cause the sea level rise by 6 millimetres. However, an exact validation of the amount is very difficult to make.

Before 2016, scientists thought of shrinking of ice sheets in Antarctica or Greenland contribute largest to the shift in Earth’s rotation due to redistribution of water. But, in 2016, Surendra Adhikari, scientist at the Jet Propulsion Laboratory, NASA, and his team brought out first about change in land water distribution can also cause a change in Earth’s rotational axis.

The 2016 study showed that the Indian subcontinent and the Caspian sea lost groundwater at a massive scale and this caused the Earth’s rotational axis to shift eastward.

Since then, scientists are looking at how land water redistribution, especially in the mid-latitude region of the planet contributes to the shift in the rotational axis. Redistribution of water in the mid-latitudes has a significance in the drift of the poles. In also the latest study it was found that during the study period most of the groundwater extraction occurred in north America and northwestern India, both lying at the mid-latitudes.

Ki-Weon Seo, the corresponding author of the study, in a statement said how the polar drift due to land water redistribution can be minimised, “Attempts to slow groundwater depletion rates, especially in those sensitive regions, could theoretically alter the change in drift, but only if such conservation approaches are sustained for decades.”

Seo’s team in the latest study analysed the shift in Earth’s rotational axis relating to water movement by considering both ice sheet and glacier melting and groundwater extraction. First they considered melting ice sheets and glacier only and then the groundwater extraction. Interestingly, when only melt water was taken, then that could not explain the polar drift. Seo, in a comment also mentioned about it, “Adding the effects of changes in surface reservoirs did not help, so I just scratched my head and said, ‘probably one effect is groundwater’.”

Another study published also in the Geophysical Research Letters in 2021said that the North Pole shifted eastward in 1995 and that this drift during 1995-2020 is nearly 17 times speedier than it was during 1981-1995