New findings on human-induced drift of Earth’s rotational pole is a wake-up call

Scientists from Seoul National University recently published a paper claiming human beings pumped water out from aquifers and its redistribution to the oceans resulted in a drift of Earth’s rotational pole, about 78.48 cm toward 64.16°E in the last 30 years.

Ki-Weon Seo from Seoul National University’s Department of Earth Science, with his colleagues,  calculated that between 1993 and 2010, 2,150 gigatonnes of groundwater was removed from aquifers across the globe.

Also read: Groundwater extraction has tilted Earth’s spin; how likely is it to fuel climate change?

Those water ultimately got accumulated in the seas and oceans. According to their model, among many contributors to the polar motion, groundwater storage changes are estimated to be the second largest, 4.36 cm per year. 

Polar motion

Polar motion refers to the movement of the Earth’s rotational axis in relation to its crust. It occurs due to the interaction of the Earth’s atmosphere, oceans, solid Earth and the fluid movements within the Earth’s core.

Change in mass distribution is one of the key drivers of Polar motion. 

In response to the change in mass distribution, the Earth’s crust gets deformed. This deformation affects the position of the Earth’s rotational axis and leads to polar motion.

Some of these reasons are seasonal. For example, the seasonal change in the atmospheric and oceanic mass distribution gives rise to a cyclic polar motion. Poles drift several meters per year and come back to their original position.

Also read: Climate crisis: Is Earth destabilising?

Some of these processes are one-directional. The melting of large ice sheets after the last Ice Age, which picked around 20,000 years ago and ended around 11,700 years ago, is one such process. This melting was known as the main contributor to the change in mass distribution.

The polar motion should not be confused with other cyclic movements of the Earth’s pole, such as eccentricity, obliquity or precession, with respect to celestial objects. Polar motion is the motion of the pole with respect to its own crust.

Contribution of aquifer pumping

Satellite data now gives more robust evidence on the polar motion. The evidence collected and the model used by Ki-Weon Seo and colleagues show that mass redistribution due to groundwater pumping has been the second largest contributor to polar motion.

For the last 100 years, the pole has been moving westward towards the green line in the picture. However, over the last 30 years, it has started moving eastward. Observational data shows it is moving in the direction of the red line. Source: Geophysical Research Letters

The model, which doesn’t include groundwater exploitation, predicts that the polar motion will be in the direction of the blue-dotted line. However, if redistribution of mass due to groundwater exploitation is taken into consideration in the model, it suggests polar motion towards the direction of the blue line. This line is closer to the observed polar motion.

In this model, they also estimated the contribution of each major factor to the drift. They found groundwater redistribution to the ocean is the second largest, causing a drift of 4.36 cm per year toward the east.

So far, the shift in Earth’s tilt is too small to impact weather or seasons. However, this is the first instance of human action impacting something such as polar motion. We need to be cautious about the impact of our actions on our surroundings and the entire planet. Impacting the polar motion through our activities is a new addition to that list.

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth

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