The consequences of climate change are so huge it is sometimes difficult to appreciate the scale of what will unfold. But climate change is already responsible for fundamental shifts that include altering the axis around which the earth spins. As temperatures rise, melting ice has re-distributed water across the earth’s surface, causing the angle of rotation to shift.
The planet’s geographic north and south poles have always wandered in response to changing ocean currents and the convection of molten rock in the earth’s core — a phenomenon known as ‘polar motion’. But the emergence of global warming in recent decades has added a new and unpredictable dimension to this age-old process.
The power of climate change to cause such a significant shift in how the earth’s axis of spin moves offers a glimpse of the enormous consequences that could follow from sea-level rise, water depletion, and ecosystem destruction. “The new polar wander is sort of like the canary in the coal mine,” says Erik Ivins, a senior research scientist at NASA's Jet Propulsion Laboratory at the California Institute of Technology.
Scientists have known for several years that climate change was behind shifts in the earth’s axis of rotation following analysis of data acquired from the GRACE satellites launched in 2002. But research published in 2021 shook up understandings of polar motion by demonstrating that man-made climate change has been having an impact for longer than anyone previously thought.
Using data on glacier loss and estimations of groundwater pumping, a team of scientists calculated how the water stored on land has changed over time. Their findings showed how water loss in both polar and non-polar regions was the main reason for a dramatic eastward movement of the poles that took place in the mid-1990s.
“There is a close relationship between the rapid decrease of terrestrial water storage and the shift of polar drift,” says Professor Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences and the corresponding author of the research article. “This is very much related to the rapid melting of glaciers that is most probably due to climate change.”
A secondary — but nonetheless significant — reason for the change, according to the research, is the pumping of groundwater from underwater reservoirs, and its subsequent re-distribution across the world’s surface. The analysis showed major changes in water mass in places like northern India, which pumps huge amounts of groundwater for use in agriculture.
Since 1980, the position of the poles has moved about 120 centimetres. But this movement has been accompanied by an acceleration in the pace of change as the effects of global warming. The average speed of drift from 1995 to 2020 was 17 times faster than the average speed recorded between 1981 and 1995.
There seems little doubt that the rate of change to the shift of the earth’s axis drift will accelerate as global warming continues and the ice in the polar regions and glaciers melts ever-more rapidly. There is already significant momentum behind the process, so polar drift will take decades to slow even if warming processes were halted more or less immediately.
“With the change of climate, it is possible to foresee a change of water storage in the future that may lead to another shift of the polar drift,” says Liu.
Experts stress that the day-to-day life of ordinary people will not be affected by changes to the ‘drift’ of the earth axis of rotation, however extreme the tilt may become. There is a chance that the length of a day may grow or shrink by a few milliseconds - something only very few are likely to notice.
The phenomenon is of great interest to academics, particularly those who study terrestrial bodies like the earth, and even stars. But Ivins at the California Institute of Technology says this doesn’t mean ordinary people shouldn’t take note of what is happening. Indeed, the very fact that changes to the earth’s axis of rotation can be caused by human activity is an indicator that something fundamental is wrong.
“Generally, when a driver of a car is aware of the functioning of the car, they look for little tell-tale signs of wear or need to examine the car for critical maintenance. Such things could be a new rattle at a certain speed, or a shaky steering wheel, unusual exhaust, a tendency of the car to veer to the right or left,” says Ivins.
“In the same way, changes to the earth’s axis of rotation help provide a measure of how ‘off kilter’ the system is.”