Nature
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Human-driven climate change has increased glacier melting in polar regions for decades. By the 1990s, the redistribution of water on Earth's surface due to glacial melt was enough to drive a shift in the planet's axis, a new study has shown.
The findings, published in Geophysical Research Letters have immediate consequences for all Earth and space sciences.
"The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s," said lead author Shanshan Deng in a statement.
As the Earth rotates around its axis, the areas where the invisible axis line intersects with the planet's surface are the North and South poles. However, the axis is not static but drifts for reasons that still remain unclear to scientists. One proposed reason is changes in water distribution on the surface of Earth.
Imagine a spinning top. If the weight of the top was moved around, it would wobble and lean as its axis rotation shifts. When mass moves around on the surface of our planet, it also causes the axis to move, and so the poles shift as a consequence. Since 2002, researchers have been able to track these changes to the planet's axis based on data provided by the Gravity Recovery and Climate Experiment (GRACE), a joint NASA and German Aerospace mission that tracks how mass is distributed around the planet by tracking uneven changes in gravity at different points across the globe.
Previous studies using GRACE data had linked the drift in Earth's axis to increases in glacier melting, however, the new findings have taken it a step further. The researchers backdated their pole tracking analysis to the 1990s before the GRACE mission was launched. They then calculated the total water loss back then to see how the poles were influenced three decades ago.
They found that in 1995 the direction of polar shift shifted from southward to eastward, and that the average speed of this drift from 1995 to 2020 was 17 times faster than it had been from 1981 to 1995.
By using the data from the water loss and groundwater data they calculated how the water stored on land had changed. Their findings revealed that the water loss due to glacier melting in the polar regions of the planet was the main driver of the eastward shift of Earth's axis, while water loss from non-polar regions also played a role in areas where large amounts of groundwater pumping are used for agricultural purposes.
"I think it brings an interesting piece of evidence to this question," said Vincent Humphrey, a climate scientist at the University of Zurich who was not involved in this research. "It tells you how strong this mass change is – it's so big that it can change the axis of the Earth."
Humphrey did note however that 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."
Nevertheless, the concerning trend continues in the polar regions as the planet warms due to climate change. More glacier melting is anticipated and with that, a more dramatic shift in the Earth's axis could result.
