Friday, August 21, 2009

Global warming will affect Earth’s tilt’

Influx Of Water From Shrinking Ice Sheets Will Change The Axis Of Rotation From The Present 23.5°

A new study has suggested that global warming may heat up oceans to the extent that it could cause Earth’s axis to tilt in the coming century. According to a report in New Scientist, the warming effect was previously thought to be negligible, but researchers now say the shift will be large enough that it should be taken into account when interpreting how the Earth wobbles. The Earth spins on an axis that is tilted some 23.5 degrees from the vertical. But this position is far from constant — the planet’s axis is constantly shifting in response to changes in the distribution of mass around the Earth.

“The Earth is like a spinning top, and if you put more mass on one side or other, the axis of rotation is going to shift slightly,” said Felix Landerer of Nasa’s Jet Propulsion Laboratory in Pasadena, California. The changing climate has long been known to move Earth’s axis. The influx of fresh water from shrinking ice sheets also causes the planet to pitch over.

Landerer and colleagues estimate that the melting of Greenland’s ice is already causing Earth’s axis to tilt at an annual rate of about 2.6 centimetres — and that rate may increase significantly in the coming years. Now, they calculate that oceans warmed by the rise in greenhouse gases can also cause the Earth to tilt — a conclusion that runs counter to older models, which suggested that ocean expansion would not create a large shift in the distribution of the Earth’s mass.

The researchers modelled the changes that would occur if moderate projections made by the Intergovernmental Panel on Climate Change — a doubling of carbon dioxide levels between 2000 and 2100 — were to become reality. The team found that as the oceans warm and expand, more water will be pushed up and onto the Earth’s shallower ocean shelves.

Over the next century, the subtle effect is expected to cause the northern pole of Earth’s spin axis to shift by roughly 1.5 centimetres per year in the direction of Alaska and Hawaii. The motion is strong enough that it needs to be taken into account when interpreting shifts in Earth’s axis. Tracking the motion of the poles could help place limits on the total amount of sea level rise over decades.

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