Earth’s poles are shifting because of climate change

By Anil Ananthaswamy
13 December 2013 (New Scientist) – Climate change is causing the North Pole’s location to drift, owing to subtle changes in Earth’s rotation that result from the melting of glaciers and ice sheets. The finding suggests that monitoring the position of the pole could become a new tool for tracking global warming. Computer simulations had suggested that the melting of ice sheets and the consequent rise in sea level could affect the distribution of mass on the Earth’s surface. This would in turn cause the Earth’s axis to shift, an effect that has been confirmed by measurements of the positions of the poles. Now, Jianli Chen of the University of Texas at Austin and colleagues have shown that melting due to our greenhouse-gas emissions is making its own contribution to the shift. The wobble in Earth’s axis of rotation is a combination of two major components, each with its own cause. One is called the Chandler wobble and is thought to arise because the Earth is not rigid. Another is the annual wobble, related to Earth’s orbit around the sun. Remove these wobbles, and you are left with an additional signal. Since observations began in 1899, the North Pole has been drifting southwards 10 centimetres per year along longitude 70° west – a line running through eastern Canada. This drift is due to the changes in the distribution of Earth’s mass as the crust slowly rebounds after the end of the last ice age. But Chen’s team found something surprising. In 2005, this southward drift changed abruptly. The pole began moving eastwards and continues to do so, a shift that has amounted to about 1.2 metres since 2005. To work out why the pole changed direction, Chen’s team used data from NASA’s GRACE satellite, which measures changes in Earth’s gravity field over time. The data allowed them to calculate the redistribution of mass on Earth’s surface due to the melting of the Greenland and Antarctic ice sheets and mountain glaciers, and the resulting rise in sea level. It correlated perfectly with the observed changes in the mean pole position (MPP). “Ice melting and sea level change can explain 90 per cent of the [eastward shift],” says Chen. “The driving force for the sudden change is climate change.” [more]