Climate change has shifted the Earth’s axis

The loss of water on earth due to melting ice and anthropogenic factors alters the movement of the North and South Poles.

The melting of glaciers due to global warming is probably the cause of a shift in the movement of the poles that occurred in the 1990s.

The locations of the North and South Poles are not static and immutable points on our planet. The axis around which the Earth rotates – or more precisely the surface from which the invisible line emerges – is always in motion due to processes that scientists do not fully understand. The way water is distributed on the Earth’s surface is a factor that causes drift.

Melting glaciers redistributed enough water to rotate and accelerate the direction of the polar wandering east in the mid-1990s, a new study found Geophysical research letters, AGU’s journal for short, high-impact reports with immediate implications covering all Earth and space sciences.

“The faster melting of the ice under the effect of global warming was the most likely cause of the change in direction of the polar drift in the 1990s,” said Shanshan Deng, a researcher at the Institute of Geographic Sciences and of natural resources of the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and author of the new study.

The Earth revolves around an axis that looks like a summit, explains Vincent Humphrey, climatologist at the University of Zurich who was not involved in this research. If the weight of a router is shifted, the router will begin to lean and oscillate as its axis of rotation changes. The same thing happens to Earth when weight is moved from one area to another.

The melting of glaciers in Alaska, Greenland, the southern Andes, Antarctica, the Caucasus and the Middle East accelerated in the mid-1990s, becoming the main engine pushing the Earth’s poles into a drift. sudden and rapid towards 26 ° E at a speed of 3.28 millimeters (0.129 inch) per year. The intensity of the colors on the map shows where changes in water stored on earth (mainly in the form of ice) had the strongest effect on pole movement from April 2004 to June 2020. Inset charts illustrate the change in glacier mass (black) and the calculated change in water on land (blue) in regions of greatest influence. Credit: Deng et al (2021) Geophysical research letters / AGU

Researchers were able to determine the causes of polar drifts from 2002 onwards based on data from the Gravity Recovery and Climate Experiment (GRACE), a joint mission of NASA and the German Aerospace Center, launched with two satellites that year and a follow-up mission in 2018. The mission gathered information on the distribution of mass around the planet by measuring uneven changes in gravity at different points.

Previous published studies of GRACE mission data have revealed some of the reasons for subsequent policy changes. For example, research has determined that the more recent movements of the North Pole away from Canada and into Russia are caused by factors like molten iron in the Earth’s outer core. Other changes were caused in part by what is known as terrestrial water storage change, the process by which all water on earth – including water frozen in glaciers and groundwater stored under our continents – is lost by the melting and pumping of groundwater.

The authors of the new study believed that this loss of water on earth had contributed to changes in polar drift over the past two decades by altering the distribution of mass around the world. In particular, they wanted to see if this could also explain the changes that took place in the mid-90s.

In 1995, the direction of the polar drift shifted from south to east. The average drift speed from 1995 to 2020 also increased about 17 times compared to the average speed recorded from 1981 to 1995.

Changes in the geographic location of the Earth’s North and South Poles are called polar drift, or true polar ambulation. Credit: NASA / JPL-Caltech

Researchers have now found a way to go back in time to modern pole tracking analysis to understand why this drift occurred. The new research calculates the total water loss from land in the 1990s before the start of the GRACE mission.

“The findings offer a clue to study past climate-induced polar motion,” said Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, University of the Chinese Academy of Sciences and the author of the new study. “The aim of this project, funded by the Chinese Ministry of Science and Technology, is to explore the relationship between water and the polar movement.”

Water loss and polar drift

Using data on glacier loss and estimates of groundwater pumping, Liu and his colleagues calculated how the water stored on earth has changed. They found that contributions from water loss from polar regions are the main driver of polar drift, with contributions from water loss from non-polar regions. Together, all of these water losses explain the eastward shift in the polar drift.

“I think this brings some interesting evidence to this question,” Humphrey said. “It tells you how important this change in mass is – it’s so important that it can change the axis of the Earth.”

Humphrey said the shift in the Earth’s axis was not large enough to affect daily life. It could change the length of the day we live in, but only by a few milliseconds.

The faster melting of the ice couldn’t fully explain the change, Deng said. Although they did not analyze this specifically, she speculated that the slight deviation could be due to activities involving the storage of terrestrial water in non-polar regions, such as the unsustainable pumping of groundwater for agriculture.

Humphrey said this evidence reveals how direct human activity can impact changes in the body of water on earth. Their analysis found big changes in the water body in areas like California, northern Texas, the area around Beijing, and northern India, for example – all areas that pumped in large amounts. groundwater for agricultural purposes.

“The contribution of groundwater is also significant,” said Humphrey. “Here, you have a problem of local water management which is taken into account by this type of analysis.”

Liu said the research had larger implications for our understanding of land water storage in the early 20’s.^e century. Researchers have 176 years of polar drift data. Using some of the methods highlighted by her and her colleagues, it might be possible to use these changes in direction and speed to estimate how much land water has been lost in recent years.

Reference: “Polar Drift in the 1990 Explained by Terrestrial Water Storage Changes” by S. Deng, S. Liu, X. Mo, L. Jiang and P. Bauer-Gottwein, March 22, 2021 ,.
DOI: 10.1029 / 2020GL092114