Researchers have used models and global positioning system (GPS) technology for more than a decade to track the movement of water from melting ice masses, the oceans and the atmosphere that cause the Earth to bulge at its equator and the North Pole to shift slightly, he told the Reno Gazette-Journal.

In recent years, however, Blewitt and his colleagues developed computer software that analyzes GPS signals more precisely, allowing them to measure changes in the shape of the Earth within a few millimeters, or about three-twentieths of an inch.

"So instead of using models, we actually observe bulges in the Earth's shape directly and relate it to the wobble," Blewitt said.

Blewitt and his fellow researchers, Richard Gross of the Jet Propulsion Laboratory and Peter Clarke and David Lavallee of the University of Newcastle-upon-Tyne, England, have published their findings in an article published in the April 1 edition of Geophysical Research Letters.

Blewitt will present his groups findings Thursday at an international science conference in Montreal.

"When people think of GPS, they usually think of finding a car on a road somewhere, not measuring the whole diameter of the Earth within a few millimeters," he said.

"But it's just been recent advancements university researchers developed in the technology of GPS that has allowed us to do that."

It provides a new method of tracking where water is moving around the planet, Blewitt said.

"Just by looking at the Earth's shape, we can see where water is moving from the ocean and where it gets deposited on land," he said. "It gives us the ability to measure how much the Earth's climate system is changing."