Brian Kahn, 23 April 2021
Of all the things attributable to climate change, the rotational poles moving differently is definitely one of the weirder ones. But a new study shows that’s exactly what’s happening. It builds on previous findings to show that disappearing ice is playing a major role, and shows that groundwater depletion is responsible for contributing to wobbles as well.
The findings, published last month in Geophysical Research Letters, uses satellites that track gravity to track what researchers call “polar drift.” While we think of gravity as a constant, it’s actually a moving target based on the shape of the planet. While earthquakes and other geophysical activities can certainly play a role by pushing land around, it’s water that is responsible for the biggest shifts. The satellites used for the study, known as GRACE and GRACE-FO, were calibrated to measure Earth’s shifting mass.
They’ve previously detected gravity changes tied to disappearing ice in Antarctica and the drought that led to groundwater depletion in California in the mid-2010s. The data can also reveal how these changes in gravity, in turn, impact the poles.
Polar drift is something that happens naturally. The Earth’s axis is slowly shifting, but there’s been a marked acceleration in recent decades. The poles are now moving at nearly 17 times the rate they were in 1981, a fairly remarkable speed-up. What’s even more remarkable, though, is that poles actually began moving in a new direction quite suddenly in 2000, at a rapid clip.
Previous research used the same satellite data to observe the speed-up and change of gear and attributed it to ice loss in Greenland and West Antarctica as well as groundwater pumping. The new study extends the record back to the 1990s and explores some of the year-to-year wobbles in more detail. The findings point to changes in groundwater use in specific regions as the source of some of those differences.
“Using the GRACE data (for the period 2002-2015) we showed that such interannual signals (as these authors pointed out: kinks at 2005 and 2012) can be explained by the terrestrial water storage,” Surendra Adhikari, a scientist at NASA Jet Propulsion Laboratory who led the 2016 research, said in an email. “The new paper reinforces the statement by also showing that another kink in the polar motion data (at 1995) is also explained by total water storage variability, especially by the on-set of accelerated Greenland ice mass loss and depletion of water storage in the Middle East and the Indian subcontinent.
“In general, the paper (along with our previous works) reveals the strong connection between the climate variability and how the Earth wobbles,” he added, noting the new study was a “nicely done paper.”
In the scheme of things, climate change triggering polar movement isn’t too worrisome, given the other clear and present dangers like intense heat waves, ocean acidification, and the sixth mass extinction. Ditto for the role of groundwater depletion, which has the potential to impact billions of lives. But it’s a powerful reminder of just how much humans have reshaped the planet and why we should probably cut it out sooner than later if we don’t want our world to turn upside down.
Correction, 4/23/21, 6:30 p.m.: This post has been updated to reflect that the rotational poles are the ones in question moving and being studied.