Global warming is shifting the way the Earth wobbles on its polar axis, a new Nasa study has concluded. Melting ice sheets – especially in Greenland – are changing the distribution of weight on Earth. That has caused both the North Pole and the wobble, which is called polar motion, to change course, according to a study published Friday in the journal Science Advances.
Scientists and navigators have been accurately measuring the true pole and polar motion since 1899 and for almost the entire 20th century they migrated a bit toward Canada.
But that has changed with this century and now it’s moving toward England, said study lead author Surendra Adhikari at NASA’s Jet Propulsion Lab.
‘The recent shift from the 20th-century direction is very dramatic,’ Adhikari said.
Although a desktop globe always spins smoothly around the axis running through its north and south poles, a real planet wobbles.
Earth’s spin axis drifts slowly around the poles; the farthest away it has wobbled since observations began is 37 feet (12 meters).
These wobbles don’t affect our daily life, but they must be taken into account to get accurate results from GPS, Earth-observing satellites and observatories on the ground.
Around the year 2000, Earth’s spin axis took an abrupt turn toward the east and is now drifting almost twice as fast as before, at a rate of almost 7 inches (17 centimeters) a year.
‘It’s no longer moving toward Hudson Bay, but instead toward the British Isles,’ said Adhikari.
Adhikari and Ivins’ calculations showed that the changes in Greenland alone do not generate the gigantic amount of energy needed to pull the spin axis as far as it has shifted.
In the Southern Hemisphere, ice mass loss from West Antarctica is pulling, and ice mass gain in East Antarctica is pushing, Earth’s spin axis in the same direction that Greenland is pulling it from the north, but the combined effect is still not enough to explain the speedup and new direction. Something east of Greenland has to be exerting an additional pull.
The researchers found the answer in Eurasia.
‘The bulk of the answer is a deficit of water in Eurasia: the Indian subcontinent and the Caspian Sea area,’ Adhikari said.
The discovery raises the possibility that the 115-year record of east-west wobbles in Earth’s spin axis may, in fact, be a remarkably good record of changes in land water storage.
‘That could tell us something about past climate — whether the intensity of drought or wetness has amplified over time, and in which locations,’ said Adhikari.
While scientists say the shift is harmless, it is meaningful. Jonathan Overpeck, professor of geosciences at the University of Arizona who wasn’t part of the study, said ‘this highlights how real and profoundly large an impact humans are having on the planet.’
Since 2003, Greenland has lost on average more than 600 trillion pounds of ice a year and that affects the way the Earth wobbles in a manner similar to a figure skater lifting one leg while spinning, said NASA scientist Eirk Ivins, the study’s co-author.
Ivins said he likes to think of it as a billion trucks each year dumping ice out of Greenland.
On top of that, West Antarctica loses 275 trillion pounds of ice and East Antarctica gains about 165 trillion pounds of ice yearly, helping tilt the wobble further, Ivins said.
They all combine to pull polar motion toward the east, Adhikari said.
Jianli Chen, a senior research scientist at the University of Texas’ Center for Space Research, first attributed the pole shift to climate change in 2013 and he said this new study takes his work a step further.
‘There is nothing to worry about,’ said Chen, who wasn’t part of the NASA study.
‘It is just another interesting effect of climate change.’
