There are various reasons why people take groundwater from the earth: for irrigation, for example, or for brewing beer. But the removal has consequences for the planet. As researchers are now reporting, the Earth’s axis of rotation has already changed because of the water extraction: The North Pole has shifted by 4.36 centimeters per year as a result between 1993 and 2010, writes a team led by geophysicist Ki-Weon Seo from Seoul National University. That’s a total of almost 80 centimeters. The net loss of groundwater in this period was estimated by climate experts at 2.15 trillion tons. They entered the sea, which corresponds to a sea level rise of 6.24 millimeters, write the researchers in the Geophysical Research Letters. So far, however, there has been a lack of direct measurement data. The pole shift study could provide independent confirmation of the numbers.
In general, the earth’s axis is not rigid at one point. “Any mass that moves on the earth’s surface can change the axis of rotation,” says Seo in an article in the journal Nature to the study.
Until recently, researchers thought that such water-related effects on the Earth’s axis were mainly caused by the melting of glaciers and ice sheets in the polar regions. However, when Seo’s team analyzed the data on ice melt and other factors, a crucial amount for shifting the earth’s axis was missing. Only when the researchers included the already suspected loss of groundwater did everything come together.
The shifting of the axis has no direct impact on people and nature
“I am very happy to have found the unexplained cause of the rotational pole drift,” said Seo. “On the other hand, as an Earthling and father, I am concerned and surprised that groundwater pumping is another cause of sea level rise.”
The new calculation of the pole shift is “absolutely plausible and correct,” says Harald Schuh from the GFZ German Research Center for Geosciences in Potsdam. This itself has no direct impact on people or nature. This also applies to further long-term changes in the position of the North Pole, for example due to the melting of glaciers or the ongoing uplift of the continents after the Ice Age. In addition, there are the natural pole fluctuations that result from the shape of the earth and the position of the earth’s axis. Therefore, the location of the North Pole varies on the order of ten to twelve meters during a year. “Nowadays you can measure the current position of the pole with an accuracy of less than a centimeter and thus also identify long-term pole movements, as in the study mentioned,” says Schuh.
The position of the pole must be measured continuously, also in order to correct navigation systems such as GPS accordingly. “You have to remember that the satellites orbit the earth on their orbits. The ‘wobbling’ of the earth’s axis underneath must therefore be taken into account, otherwise you just make an error of more than ten meters,” says Schuh. Experts are currently determining the pole fluctuations using so-called geodetic space methods. According to Schuh, either satellites orbiting the earth or quasars, extremely bright centers of galaxies that are so far away from the earth that they represent unchangeable fixed points in the sky, are used for this purpose. In Germany, the GFZ and the Federal Agency for Cartography and Geodesy in Frankfurt am Main are involved in the measurements.
According to the authors of the study, the redistribution of groundwater from the mid-latitudes has a particularly large impact on the North Pole. During the study period, the greatest groundwater loss occurred in large areas in western North America and northwestern India, both of which are mid-latitudes.
According to the Federal Institute for Geosciences and Natural Resources, there are no exact figures for the development of groundwater reserves in Germany. In principle, however, the many years of below-average precipitation in the last decade and the warmer and drier summers have had a negative impact on the groundwater in Germany.