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Πηγή: New scientist

8 April 2016

Why the North Pole is now slowly moving towards London

The North Pole is on the move. The real one, not this pole stuck in the ice

Sue Flood/Getty

London is calling. The planet’s North Pole mysteriously changed the direction of its travel in 2000, turning eastwards towards the Greenwich meridian. It now seems that this change in direction is down to the redistribution of water on land as well as to melting polar ice.

The Earth’s rotational axis, and with it the location of the physical North Pole, was travelling at a rate of about 10 centimetres a year over the last century towards Canada’s Hudson Bay along a line of longitude that runs through Toronto and Panama City.

This movement was down to the redistribution of Earth’s mass as the crust has slowly rebounded after the end of the last ice age.

But since 2000 it has made a dramatic 75-degree eastward shift heading along the Greenwich meridian. Some evidence suggested that the shrinking of ice sheets in Greenland and Antarctica caused by climate change was behind the surprise shift.

Now, a study says this change is also influenced by the changing distribution of water on land.

“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,” says lead researcher Surendra Adhikari of NASA’s Jet Propulsion Laboratory in Pasadena, California.

For example, Adhikari says, the Indian subcontinent and the Caspian Sea are losing a massive amount of water, pulling the axis eastwards.

Always on the move

The study used data from NASA’s GRACE satellites to investigate how the distribution of water mass was related to the direction of Earth’s axis movement between 2002 and 2015.

The results also shed light on another long-standing puzzle: why the axis oscillates every few years. This oscillation is also down to changes in water mass around the planet, says Adhikari.

“The precise knowledge of polar motion, and Earth rotation in general, is indispensable for many applications,” says Florian Seitz of the German Geodetic Research Institute in Munich. This includes GPS navigation systems and the positioning of satellites. The findings could also help us study climate change, he says.

Because we have an accurate record of the axis’s movement since 1899, we may now be able to use that data to map out past changes in the distribution of land water more precisely.

This, in conjunction with factoring in where the axis is heading, could help make climate models more accurate.

Journal reference: Science Advances, DOI: 10.1126/sciadv.1501693