EARTH SPIN
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. NASA/JPL-Caltech

Climate change affects not only the ice sheets, sea levels and human health, but turns out it even leads to shift in the Earth's poles. Melting of the Greenland ice sheet and the water deficit in the Indian sub-continent have caused a massive shift in mass distribution on the planet, causing the north pole to take a sharp turn to the east. The wobble in Earth's rotation every six to 14 years observed since 1899 is due to changes in land water storage.

The pole drift eastward was first noticed in 2000 and attributed in a 2013 University of Texas at Austin study to accelerated melting of Greenland ice. Now a new study published in Science Advances, by geophysicists from NASA Jet Propulsion Laboratory suggests that the drift of the poles cannot be wholly accounted unless considering changes in the amount of water held within the continents.

Using Nasa's Gravity Recovery and Climate Experiment (Grace) they conclude that in addition to the Greenland melt, the dry spell in Eurasia is driving the north pole eastwards by virtue of the continent shedding some weight.

The geographical poles wobble also due to variations in the pull by the sun and moon and the motion in the planet's core and mantle. But this is the first time it has been shown that the poles could drift due to the distribution of snow and rainfall change.

The north pole began drifting westwards around 10,000 years ago after the ice age when the massive ice sheets sitting on Canada melted. Under the loss of bulk the depressed crust rebounded and resulted in change in mass distribution of the planet. This pattern was seen in data from 1899 onward, registering a 12 metres movement in 115 years.

The recent turn to the east is a change in the earlier drift and shows the rate is twice as fast as before, at almost 7 inches (17 centimeters) a year. The changes in Greenland alone do not generate the gigantic amount of energy needed to pull the spin axis as far as this, the Nasa duo contended.

"It's no longer moving toward Hudson Bay, but instead toward the British Isles," said Surendhra Adhikari. "That's a massive swing."

Water loss from droughts and aquifer depletion
Adhikari and Erik Ivins calculated how much mass was involved in water cycling between Earth's land areas and its oceans from 2003 to 2015, and the extent to which these gains and losses pushed on the spin axis. The deficit of water in the Indian subcontinent and the Caspian Sea area was the missing link which explained the pole drift. Though not much by themselves, by virtue of being located on the 45 deg latitude, their effect on the spin axis is strong.

The water content on the continents also explained the wobble in Earth's rotation observed since 1899. Every six to 14 years, the spin axis wobbles about 20 to 60 inches (0.5 to 1.5 meters) either east or west.

Turns out that dry years in Eurasia, for example, corresponded to eastward swings, while wet years corresponded to westward swings. The east-west wobbles in Earth's spin axis could be a good way of looking at changes in land water storage in the past.

EARTH WOBBLE
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). NASA/JPL-Caltech