Monday 24th August 2009
In a new study due to be published in the journal Geophysical Research Letters, a team of researchers has found that sea level rise caused by warming oceans also plays a significant role in pushing the poles around.
As ocean temperature increases, the water literally expands, pushing sea levels up. Conservative estimates call for this effect to raise the global shoreline by about 3 millimeters (0.12 inches) per year over the next century -- a cumulative increase of about 1 foot.
"As warming gets into the deep ocean, it pushes up the water above it," said Felix Landerer of Jet Propulsion Laboratory in Pasadena, Calif. "Some of the mass gets transferred up onto shallow continental shelves."
The additional water sloshing up into the shallows is heavy enough to nudge the planet's rotational axis slightly closer to Alaska.
"It's a completely unexpected result," Richard Gross, also of Jet Propulsion Laboratory, said. He was not involved in the study. "The conventional thinking has been that... sea level changes won't affect Earth's rotation."
The team's finding illustrates how profoundly human activity meddles with the Earth. Increasing greenhouse gases are not only driving up temperatures, but also changing the orientation of the entire planet.
Melting ice sheets will have an even bigger effect on Earth's rotation. In particular, Greenland's ice acts like an enormous, heavy welt plopped haphazardly on Earth's spinning top. As the ice melts, it flows into the oceans, redistributing the weight.
Melt water from Greenland only raises sea level up around 0.2 millimeters (0.01 inches) each year, but it moves the pole the same amount as warming.
"Greenland melting has about a ten times stronger effect on polar motion," Landerer said. As the ice sheet continues to disintegrate in the future, he added, "the effects on polar motion will be dominated by Greenland."
Michael Reilly, Discovery News