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Thursday, April 28, 2016

Global warming changing tilt of Earth's spin axis

The Age
Date: April 15, 2016
Peter Spinks
Fairfax Science Columnist


For the first time, human activity has caused a shift in the tilt of Earth's spin axis, which could affect GPS and other satellite measurements.

For the first time, the growing ecological footprint of humans has caused the whole planet to change its tilt.

The shift in the tilt of the Earth's axis, which could affect some satellite data, including GPS systems, was revealed by NASA scientists following a careful analysis of satellite data revealing a major redistribution of water and ice around the globe.


This needs to be taken into account when interpreting some satellite data and making precise measurements using GPS. Professor Matt King, University of Tasmania

This was the result of global warming causing hundreds of billions of tonnes of ice to melt every year in Greenland and west Antarctica, coupled with a deficit of water in Eurasia, the scientists concluded.



This major ice sheet in western Antarctica is melting. Its collapse is likely to raise global sea level by almost 60 centimetres. Photo: AFP, NASA

"The axis around which our planet spins moves through time, drifting and wobbling as water moves around the planet," University of Tasmania geodesist Matt King said. Having once tilted towards Canada, the polar axis is now drifting towards Britain at roughly 16 centimetres a year, the NASA measurements reveal.
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"By using radio telescopes to observe stars and other celestial bodies, we can carefully track the position of Earth's axis," Professor King said. NASA found the axis shifted dramatically from its long-term path, first in 2005 and again in 2012.

"The axis drift observed by the radio telescopes was explained by the satellite measurements which track the mass movements and could be used to predict the change in axis drift," Professor King said.



The axis around which the Earth spins has shifted.Photo: iStock

The movements point to huge changes in the storage of water on Earth, including the loss of water in the Indian subcontinent and the Caspian Sea area as a result of depleted aquifers and drought. (The spin axis is particularly sensitive to changes occurring north and south of 45 degrees latitude.)

"The redistribution of water actually shifts the centre of Earth's mass by a few millimetres, so it's not just the axis that has changed," Professor King said.

Although we would not notice the shifts, there is a small but detectable effect on orbiting satellites.

"This needs to be taken into account when interpreting some satellite data and making precise measurements using GPS," Professor King said.

It might also mean some people receive poorer or better mobile telephone coverage than previously.




The new research helps scientists understand where the planet's ice is melting, where water is being stored on land and how these things are changing over time.

"In particular, it shows that changes in water storage on the continents have had an important effect in recent years," he said.

This is also happening in west Antarctica, due mainly to relatively warm ocean water reaching the continental shelf, where it comes in contact with ice flowing off the Antarctic continent.

"That melts and thins the ice," Professor King said. "The glaciers are then slightly steeper and the ice flows faster and thins further, increasing sea levels."

This is also happening in parts of east Antarctica, but has been offset in the past decade by heavy snowfalls.

"Overall, the consensus is that Antarctica is losing more ice to the oceans than is being replaced by snowfall, which is contributing to rising sea levels," Professor King explained.

Greenland's ice is also being melted by the ocean.

The air there was warm enough to melt the top surface, Professor King said, "so Greenland's ice sheets are being attacked from the edges and above".

"The new findings open an intriguing new pathway to connect events relating to past climate change with swings in Earth's spin axis," Sydney University geophysicist Dietmar Muller said.

Australian National University earth scientist Dr Phil Cummins agrees.

"It's remarkable that humans are actually affecting the movement of the entire planet, even if it's only a slight effect that most people won't notice," he said.


Read more: http://www.theage.com.au/technology/sci-tech/global-warming-is-changing-the-earths-tilt-20160413-go5tgb.html#ixzz46q1sjVJw
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