The position of Earth's axis has dramatically shifted, likely because of melting ice sheets (fueled by climate change) and natural changes in water storage on land, according to a new study in the journal Science Advances.
Erik Ivins, senior research scientist at NASA's Jet Propulsion Laboratory and co-author of the study published on Friday, told The Huffington Post that the movement of water on Earth's surface affects the planet's distribution of mass -- and its axis -- much like adding weight to a spinning top.
"If you considered a spinning top, and then placed a piece of chewing gum on the top, it would start spinning around a new axis," Ivins said in an email. "On the Earth, since water can be transported in and out of the oceans to the land -- affecting global mean sea-levels -- this also changes the moments of inertia, in exact analogy to the piece of chewing gum on a spinning top."
Earth, as many of us remember from grade school, spins on an axis. This axis is an imaginary line that stretches through the center of the planet from the North Pole to the South Pole, and is tilted at an angle of around 23.5 degrees with respect to the orbital plane that includes the sun and Earth.
Scientists have long known that Earth tends to wobble as it spins, causing its poles to drift slightly. However, a dramatic shift occurred around the year 2000, when the North Pole turned east.
In an attempt to understand why, Ivins and his colleague Surendra Adhikari analyzed space geodetic and satellite gravimetric data from 2003 to 2015. This data allowed the researchers to unambiguously identify the causal mechanism for the Earth's drifting poles after 2003.
The researchers wrote in their study that the Earth’s spin axis has been shifting 75-degrees eastward from its normal long-term drift direction since the early 2000s.
"In this paper we are talking about shift in 'drift direction,'" Adhikari told HuffPost in an email. "The pole used to be heading along ~75 degree west longitude, toward Canada, during the 20th century. It is now heading along the central meridian, i.e. 0 degree longitude, toward the U.K. So, this shift in direction would roughly be about 75 degrees to the east, from Canada to the U.K."
That shift, the researchers found, is being driven not only by melting ice sheets, but also a loss of water mass in Eurasia due to the depletion of aquifers and drought, according to a NASA release.
"This is the first time we have solid evidence that changes in land water distribution on a global scale also shift which direction the axis moves to," Adhikari, lead author of the study, told New Scientist.
Jonathan Overpeck, professor of geosciences at the University of Arizona, who was not involved with the study, told The Guardian that "this highlights how real and profoundly large an impact humans are having on the planet."
While the findings are surprising, Ivins said, there is no need for alarm. The shift, he said, is relatively small, and there is no real chance that the amount of solar radiation reaching sensitive parts of Earth will increase.
"What the shift does tell scientists," Ivins said, "is that we have a new tool to probe past climate changes in a very quantitative and accurate way. To us, that is significant."
This article was updated with a quote from Adhikari, explaining the 75-degrees eastward shift.