Between 1993 and 2010 alone, the Earth’s axis of rotation was tilted nearly 80 cm to the east.
By extracting water from underground to store it in dams or channel it to other places, man has moved a mass of water so large that the Earth tilted almost 80 centimeters to the east between 1993 and 2010 alone. This is the extraordinary conclusion of a study conducted by an international team of researchers and recently published in ‘ Geophysical Research Letters‘. The scientists based their calculations on previous studies, such as one published in the same journal in 2010, which estimated that humans had pumped out about 2,150 gigatons of groundwater since 1993, the equivalent of a global rise in sea level. just over 6mm. To verify the effects of the displacement of this enormous mass of water, the researchers decided to study the movements of the earth’s rotation pole, i.e. the point around which the entire planet rotates, and not to be confused with the magnetic pole, which it also moves, but for other reasons. Variations in the position of the pole of rotation relative to the crust are collectively known as polar motion. The point is that the distribution of water on the planet affects how mass is distributed, and in the same way that a top will spin differently if we add some weight on one side, the Earth will do the same as water. from which it moves from one place to another. “The pole of rotation of the earthsays Ki-Weon Seo, a geophysicist at Seoul National University who led the research,it actually changes a lot. Our study shows that among climate-related causes, groundwater redistribution actually has the greatest impact on pole shift “.
On the graph, the red arrow shows the observed shift of the pole of rotation. This shift coincides with what the models attribute to water abstraction (solid blue arrow), but would not exist without said abstraction (dashed blue arrow).
The ability of water to alter the Earth’s rotation was discovered in 2016, but the specific contribution of groundwater to these rotational changes had not been explored until now. In the new study, Seo and his colleagues modeled the observed changes in the rotational drift of the earth poles and in water movements, first considering only ice sheets and glaciers, and then adding various groundwater redistribution scenarios to the model. The data leave little room for doubt. The pattern, in fact, only matched the observed polar drift once the researchers included i 2,150 gigatons of human groundwater redistribution. Without this data, the model showed a deviation of 78.5 centimeters for the period considered, or 4.3 centimeters of deviation per year between 1993 and 2010.”I am very proud to have found the hitherto unexplained cause of the pole rotation drift“Seo says. ”On the other hand, as an Earth resident and parent, I am concerned and surprised to see groundwater pumping as another source of sea level rise“. The position of the groundwater, therefore, is important because it is able to modify the polar drift. The study shows, for example, that redistribution of water from mid-latitudes has a greater impact on the rotation pole. During the period considered (1993-2010), most of the water was redistributed in western North America and northwestern India, both in mid-latitudes. According to Seo, attempts by countries to reduce groundwater depletion rates, especially in those sensitive regions, have the potential to alter polar drift shift, especially if such conservation efforts are sustained for decades. Reassuringly, however, the researchers note that the pole of rotation naturally shifts up to several meters a year, so changes due to water redistribution they do not represent a change of seasons risk. But on geological timescales, that human contribution can make a difference and end up having a major impact on climate. The next step, then, is to try to understand how this relationship between the redistribution of water and the motion of the spin pole evolved in periods prior to 2010.”The observation of changes in the earth’s rotation pole -explains Seo- it is very useful for understanding the variations of water accumulations on a continental scale. Polar motion data has been available since the late 19th century. So we can potentially use that data to understand changes in inland water storage over the past 100 years. Has there been any change in the hydrological regime due to global warming? Polar motion may hold the answer“.