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NASA: Global warming is now changing how Earth wobbles

Melting ice sheets—especially in Greenland—are changing the distribution of weight on Earth. And 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.
NASA: Global warming is now changing how Earth wobbles
Earth does not always spin on an axis running through its poles. Instead, it wobbles
 irregularly over time, drifting toward North America throughout most of the 20th 
Century (green arrow). That direction has changed drastically due to changes
 in water mass on Earth [Credit: NASA/JPL-Caltech]
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.

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."

NASA: Global warming is now changing how Earth wobbles
Before about 2000, Earth's spin axis was drifting toward Canada (green arrow, left globe). 
JPL scientists calculated the effect of changes in water mass in different regions (center globe)
 in pulling the direction of drift eastward and speeding the rate (right globe)
 [Credit: NASA/JPL-Caltech]
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.

NASA: Global warming is now changing how Earth wobbles
NASA: Global warming is now changing how Earth wobbles
The relationship between continental water mass and the east-west wobble in Earth's 
spin axis. Losses of water from Eurasia correspond to eastward swings in the general
 direction of the spin axis (top), and Eurasian gains push the spin axis 
westward (bottom) [Credit: NASA/JPL-Caltech]
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."

Author: Seth Borenstein | Source: The Associated Press [April 08, 2016]

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