New research says that the redistribution of water thanks to glacial melting driven by climate change has been causing the Earth to shift on its axis.
The catastrophic effects of climate change on our planet cannot be overstated. But, new research shows that these effects could be even more fundamental than we previously knew.
The melting of glaciers brought about by global warming could have actually been causing shifts in the Earth’s axis of rotation. That is the conclusion of a new study that finds glacial melting has been the cause of movement in the Earth’s poles since the 1990s.
The axis around which Earth turns and thus the locations of the North and South poles aren’t static, in fact, they move constantly. Vincent Humphrey, a climate scientist at the University of Zurich explains that in this respect Earth spins like a child’s top. And just like with that toy, if the weight is redistributed, the rotational axis shifts.
Whilst scientists aren’t exactly sure how this happens, one of the prevailing theories regarding the major mechanism behind that drift is how water is distributed across the planet’s surface. This migration of the poles is called polar wander, and it seems that since the mid-90s the melting of glaciers has redistributed enough water to alter its direction shifting it eastward.
“The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s,” explains Shanshan Deng, a researcher at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences.
Deng is one of the authors of the new study detailing the research in the latest edition of the American Geophysical Union’s journal Geophysical Research Letters.
Assessing Polar Drift with GRACE
Assessing polar drift since 2002 has been possible thanks to data provided by NASA and the German Aerospace Center’s (DLR) Gravity Recovery and Climate Experiment (GRACE).
The mission which comprised of two satellites launched in 2002 and was succeeded by a follow-on mission (GRACE-FO) the year after it was decommissioned in 2017. GRACE and GRACE-FO measure how mass is distributed across Earth by monitoring gravitational anomalies.
Previous data released by the missions has allowed researchers to determine the movement of the North Pole away from Canada and towards Russia as a result of shifts in the planet’s molten iron outer core. The mission has also shown how terrestrial water storage change —water lost from the land to the sea through things like glacial melting and groundwater pumping — can cause polar drift shifts.
For their new study, in particular, the authors wanted to see if this phenomenon could explain shifts that occurred in the mid-90s. This includes the change from southward drift to eastward drift that occurred in 1995. This change in direction was also accompanied by accelerating drift speed, with speeds recorded between 1995 and 2020 topping speeds recorded from 1981 to 1995 by as much as 17 times.
To discover the nature of these changes and what drove them the team found a way to ‘wind back’ pole tracking through time, thus calculating land water losses that occurred in the 1990s before GRACE data was available.
“The findings offer a clue for studying past climate-driven polar motion,” says Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and the corresponding author of the new study. “The goal of this project, funded by the Ministry of Science and Technology of China is to explore the relationship between the water and polar motion.”
Connecting Water Loss and Polar Drift
Winding back time on land water loss and by using data to estimate groundwater pumping and glacier loss the team was able to discover that water loss from polar regions has been the main cause of polar drift, driving that eastward drift.
“I think it brings an interesting piece of evidence to this question,” Humphrey, who was not directly involved in the research, says. “It tells you how strong this mass change is — it’s so big that it can change the axis of the Earth.”
Of course, this shift in the Earth’s axis isn’t significant enough to have an effect on our day to days lives. It could length our days, but only by a matter of milliseconds.
Though the main factor in driving polar drift, water loss from polar regions and the melting of glaciers couldn’t entirely explain the trends seen since the mid-90s. The team believes that this gap in their estimates is the result of water loss from non-polar regions.
In particular, Deng points to a small contribution from groundwater pumping in non-polar regions and as a result of water use in agriculture.
One of the most important aspects revealed by the study is how much human activity can impact land water mass changes. The research revealed in particular large changes in water mass in regions such as Beijing, Nothern India, and areas in the US such as Texas and California, all of which seem to have been caused by the pumping of groundwater for agriculture.
“The groundwater contribution is also an important one,” Humphrey concludes. “Here you have a local water management problem that is picked up by this type of analysis.”
Beyond this study, the team believes that they could now take data on polar drift that has been collected over the past 176 years and apply their newly found methodology to it to develop a history of land water loss.
By doing this, Liu says that the larger implications of land water storage throughout the 20th Century could finally be understood.
Deng. S., Liu. S., Mo. X., Jiang. L., Bauer-Gottwein. P., , ‘Polar Drift in the 1990s Explained by Terrestrial Water Storage Changes,’ Geophysical Research Letters, [https://doi.org/10.1029/2020GL092114]
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