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PICTURE: The melting of glaciers in Alaska, Greenland, the southern Andes, Antarctica, the Caucasus, and the Middle East that accelerated in the mid-1990s. GEOPHYSICAL RESEARCH LETTERS / AGU
WASHINGTON – The melting of glaciers due to global warming is likely what caused a shift in the movement of the poles in the 1990s.
The locations of the North and South Poles are not static, unchanging points on our planet. The axis around which the earth rotates – or more precisely the surface from which the invisible line emerges – is always moving due to processes that scientists do not fully understand. The way water is distributed on the earth’s surface is one factor that drives drift.
Melting glaciers distributed enough water to turn and accelerate the direction of polar migration eastward in the mid-1990s. This emerges from a new study in Geophysical Research Letters, the AGU’s journal for meaningful, short-format reports with immediate effects on the entire earth and space science.
“The faster melting of the ice under global warming was the most likely cause of the polar drift change in direction in the 1990s,” said Shanshan Deng, a researcher at the Institute of Earth Sciences and Natural Resource Research, China Academy of Sciences University of China Academy of Sciences Sciences and author of the new study.
The earth rotates like a point around an axis, explains Vincent Humphrey, a climate researcher at the University of Zurich who was not involved in this research. When the weight of a convertible top is moved, the top begins to tilt and wobble as its axis of rotation changes. The same thing happens to the earth when weight is shifted from one area to another.
The researchers were able to determine the causes of polar shifts from 2002 onwards using data from the Gravity Recovery and Climate Experiment (GRACE), a joint mission by NASA and the German Aerospace Center, which was launched this year with two satellites, and a follow-up mission The mission collected information on how the mass is distributed on the planet by measuring uneven changes in gravity at different points.
Previous studies on the GRACE mission data have shown some reasons for later changes in direction. For example, research has found that recent movements of the North Pole from Canada to Russia are caused by factors such as molten iron in the Earth’s outer core. Other shifts have been caused in part by what is known as the change in terrestrial water storage, in which all water on land – including frozen water in glaciers and groundwater stored on our continents – is lost to melting and groundwater pumps.
The authors of the new study believed that this loss of water on land contributed to the shifts in polar drift over the past two decades by changing the distribution of mass around the world. In particular, they wanted to see if this could explain changes that occurred in the mid-1990s.
In 1995 the polar drift shifted from south to east. The average drift speed from 1995 to 2020 also increased 17 times compared to the average speed measured from 1981 to 1995.
Now researchers have found a way to turn modern pole tracking analysis backwards in time to find out why this drift occurred. The new study calculates the total land water loss in the 1990s prior to the start of the GRACE mission.
“The results provide a clue to studying past climatic polar movement,” said Suxia Liu, a hydrologist at the Institute of Geosciences and Natural Resource Research of the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences, and the corresponding author of the new Study. “The aim of this project, funded by the Chinese Ministry of Science and Technology, is to study the relationship between water and polar movement.”
Water loss and polar drift
Liu and her colleagues used data on glacier loss and estimates of groundwater pumping to calculate how water stored on land has changed. They found that the contributions of water loss from the polar regions are the main drivers of polar drift, with contributions from water loss in non-polar regions. Together, all of this water loss explained the change in polar drift to the east.
“I think it brings interesting evidence to that question,” said Humphrey. “It shows you how big this mass change is – it’s so big that it can change the Earth’s axis.”
Humphrey said the change in the Earth’s axis was not big enough to affect daily life. It could change the length of the day we experience, but only by milliseconds.
The faster melting of the ice could not fully explain the shift, Deng said. Although they did not specifically analyze this, they speculated that the slight gap could be due to activities involving the storage of land water in non-polar regions, such as unsustainable groundwater pumping for agriculture.
Humphrey said this evidence shows how much direct human activity can have an impact on changes in water mass on land. Their analysis revealed large changes in water mass in areas such as California, northern Texas, the Beijing region, and northern India – all areas where large amounts of groundwater were pumped for agricultural purposes.
“The groundwater contribution is also important,” said Humphrey. “Here you have a local water management problem that is captured by this type of analysis.”
Liu said the research had greater implications for our understanding of land water storage in the early 20th century. The researchers have 176 years of polar drift data. Using some of the methods she and her colleagues highlighted, it may be possible to use these changes in direction and speed to estimate how much landwater has been lost in recent years.
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