Climate has shifted axis of Earth, says study

View of planet Earth from space.
Composite image built from 15 satellite passes shows the Arctic and northern latitudes. Image via Norman Kuring/ NASA/ GSFC/ Suomi NPP.

Glacial melting due to global warming is likely the cause of a shift in the movement of Earth’s poles that occurred in the 1990s, says a new study.

The locations of the North and South Poles are not fixed. Earth’s spin axis – an imaginary line that passes through the North and South Poles – is always moving, due to processes scientists don’t completely understand. The way water is distributed on Earth’s surface is one factor that causes the axis, and therefore the poles, to shift.

According to the study, published March 22, 2021, in Geophysical Research Letters, melting glaciers redistributed enough water to cause the direction of polar wander to turn and accelerate eastward during the mid-1990s.

Shanshan Deng, a researcher at the University of the Chinese Academy of Sciences, is lead author of the new study. Deng said in a statement:

The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s.

Diagram: two Earths with axis different in each one.
Shifts in the geographic location of Earth’s North and South Poles is called polar drift, or true polar wander. Image via Victor C. Tsai/ AGU.

The Earth spins around an axis kind of like a top, explained University of Zurich climate scientist Vincent Humphrey (Humphrey was not involved in this research). If the weight of a top is moved around, he said, the spinning top would start to lean and wobble as its rotational axis changes. The same thing happens to the Earth as weight is shifted from one area to the other.

The study authors believed that this water loss on land contributed to the shifts in the polar drift in the past two decades by changing the way mass is distributed around the world. To determine the causes of polar drifts starting from 2002, the researchers used data from the GRACE satellite mission, which gathers information on how mass is distributed around the planet by measuring uneven changes in gravity at different points. The new research was particularly focused on shifts in Earth’s tilt in the 1990s. To calculate the total land water loss in the 1990s – before the GRACE mission started in 2002 – the researchers used data on glacier loss and estimations of ground water pumping to calculate how the water stored on land changed.

Their analysis determined that in 1995, the direction of polar drift shifted from southward to eastward. The average speed of drift from 1995 to 2020 also increased about 17 times from the average speed recorded from 1981 to 1995. They found that the contributions of water loss from the polar regions was the main driver of the polar drift, with contributions from water loss in non-polar regions. Together, all this water loss explained the eastward change in polar drift.

The Guardian reported:

Gravity data from the GRACE satellite, launched in 2002, had been used to link glacial melting to movements of the pole in 2005 and 2012, both following increases in ice losses. But Deng’s research breaks new ground by extending the link to before the satellite’s launch, showing human activities have been shifting the poles since the 1990s, almost three decades ago.

Although the research showed glacial losses accounted for most of the shift, Deng said it is likely that activities involving land water storage – such as the pumping of groundwater – also contributed to the movements.

Humphrey said:

I think it brings an interesting piece of evidence to this question. It tells you how strong this mass change is: it’s so big that it can change the axis of the Earth.

He said the change to the Earth’s axis isn’t large enough that it would affect daily life. It could change the length of day we experience, but only by milliseconds.

Bottom line: A new study says that climate change has altered Earth’s tilt on its axis.

Source: Polar Drift in the 1990s Explained by Terrestrial Water Storage Changes


Via The Guardian

April 28, 2021

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