Humanity's impacts on our planet's climate are so profound, we have for decades been unwittingly shifting the very axis upon which Earth spins around, scientists say.
In a new study, researchers examined the phenomenon of true polar wander, in which the geographic locations of Earth's north and south poles drift with respect to the planet's rotational axis.
This mysterious phenomenon is thought to be influenced by a number of factors, including, it now seems, the effects of anthropogenic (human-caused) climate change.
"Faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s," explains lead researcher Shanshan Deng from the Institute of Geographic Sciences and Natural Resources Research in China.
In the new study, Deng and fellow researchers examined the extent to which changes in terrestrial water storage (TWS) in recent decades contributed to the amount of true polar wander recorded in the same timeframe.
Basically, TWS includes changes in water levels on Earth resulting from glaciers melting as the world gets warmer, in addition to changes also produced by the pumping of groundwater from underground reservoirs.
The reason these changes are important is because they affect the distribution of mass on Earth, and when you're dealing with a spinning object – whether a spinning top, a yo-yo, or an entire planet revolving in space – the way its mass is distributed in turn affects the way it spins.
"It brings an interesting piece of evidence to this question," explains climate scientist Vincent Humphrey from the University of Zurich in Switzerland, who wasn't involved with the study.
"It tells you how strong this mass change is – it's so big that it can change the axis of the Earth."
While polar drift is a natural phenomenon that has been observed by scientists for over a century, the level of wander is not constant, evidenced by a pronounced directional change from westwards to eastwards that was first seen in the 1990s.
According to the team's calculations – based on satellite data from NASA's Gravity Recovery and Climate Experiment (GRACE) mission and estimates of glacier loss and groundwater pumping going back to the 1980s – the primary driver of polar drift change seen in the 1990s was ice melt due to climate change.
"The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s," the researchers explain in their study.
"The other possible causes are TWS change in non‐glacial regions due to climate change and unsustainable consumption of groundwater for irrigation and other anthropogenic activities."
While the degree of axis shift experienced so far is estimated to be so slight that humans wouldn't be able to perceive it in daily life, the results nonetheless suggest another alarming side effect of humanity's unsustainable usage of Earth's resources: planetary-scale mass rearrangements significant enough to measurably affect the revolutions of the world we live upon.
Another question is how much ongoing, locked-in ice melting – and continued plundering of groundwater resources – might impact future axis shifting, and what ramifications could result from that. We'll have to wait and see.
The findings are reported in Geophysical Research Letters.
Editor's note (27 Apr 2021): The original version of this story contained a number of errors with regard to the nature of the phenomenon of polar wander. The article has been corrected. ScienceAlert regrets the mistake.