The North Pole and South Pole look stable on maps. In reality, both poles are gradually drifting because the Earth wobbles slightly as it spins on its axis. The North Pole has drifted slightly toward North America throughout most of the 20th century due to this wobbling.
But scientists found something anomalous in 2000. The North Pole mysteriously switched direction and started moving east toward the Greenwich meridian at almost twice its previous speed—at a rate of seven inches a year. In other words, the North Pole is no longer moving toward Hudson Bay but rather toward the British Isles. This was a mystery that baffled geologists for years.
Researchers Surendra Adhikari and Erik Irvins of the Jet Propulsions Laboratory at NASA finally figured out why. Their study involved analysing data from the NASA GRACE satellites to determine whether water mass across the planet was related to the spin axis of the Earth.
The GRACE satellites pinpointed positive gravity anomalies. These anomalies are indicator that there is more mass in a particular region. The only explanation for this apparent sudden shift of mass is the movement of water on a huge scale.
Findings revealed that the movement of water around the world contributes to the rotational wobble of the Earth. There is thereby a strong link between water mass and the wobbles in the spin axis of the Earth. The findings also revealed that human activities are pretty much to blame of the current wobble or movement of the North Pole toward the Greenwich meridian. These activities have been affecting the movement and distribution of water across the globe.
Some scientists have already hypothesised that water was playing a role in the wobbling of the Earth and the movement of the North Pole. Some evidences suggested that this phenomenon was due to climate change and the melting of the Greenland Ice Sheet.
The study of Adhikari and Irvins demonstrated that the changes in Greenland alone were not enough to generate the gigantic amount of energy needed to pull the spin axis as far as it has shifted. Of course, in the Southern Hemisphere, the ice mass loss from West Antarctica is pulling and the ice mass gain in East Antarctica is pushing in the spin axis of the Earth in the same direction that Greenland is pulling it from the north.
But the combined effect was not enough to account for the new direction and the speedup. The NASA researchers realized that something east of Greenland has to be exerting an additional pull.
Further analysis of the data revealed that the water deficit in Eurasia—particularly the Indian subcontinent and the Caspian Sea area—was contributing considerably to the phenomenon. This was surprising. Accordingly, Eurasia has lost water mass due to drought and the depletion of aquifers. However, this loss was nowhere near as massive as the changes in the ice sheets.
The theory of rotating objects explains why this relative minimal loss of water in Eurasia has considerably affected the spin axis of the Earth. Adhikari and Irvins explained that the spin axis is very sensitive to changes occurring around 45 degrees latitude.
A notable takeaway from this study is that it provides a new model for explaining the wobbling of the Earth. Take note that the spin axis wobbles about 20 to 60 inches either east or west of its general direction drift every six to 14 years. By comparing the GRACE data and the graph of changes in continental water storage collected for the same period, Adhikari and Irvins concluded that changes in polar ice appeared to have no relationship to the wobble.
Changes in water on land appeared to have contribution to the wobble instead. For example, analysis of the two sets of data revealed that dry years in Eurasia corresponded to eastward swings while wet years corresponded to westward swings.
The results suggested that the relationship between land water mass in Eurasia and spin axis wobble is more than a simple correlation. The NASA researchers have isolated the cause.
Another takeaway from this study is that it provides insights about the water distribution across the Earth in the past. In addition, the study also introduces a novel model for predicting the movement of the North Pole and South Pole in the future.
The wobble of the Earth does not have far-reaching effect on daily lives. However, it is important take into account that moving poles could affect the accuracy of GPS and other satellite or observation tools.
Further details of the study of Adhikari and Irvins are in the article “Climate-driven Polar Motion: 2003-2015” published in April 2016 in the journal Science Advances.