Earth Girth
Melting ice is expanding the planet's waistline
The Science
Ice loss from Greenland and Antarctica sends more water into the oceans leading to a "fatter" Earth.
pressure of land-based ice has reduced as the ice melted, the land underneath has "rebounded" causing Earth to become more spherical, he said. "It is a bit like a sponge, it takes a while to come back to its original shape."
In the mid-1990s that trend changed; however, as the planet appeared to start flattening out again, Nerem said. Puzzled by this observation, the scientific community came up with theories as to why this might be the case. "But a lot of it was speculation, albeit informed speculation," he said.
That was until the launching of the GRACE satellite mission. Using the high-resolution GRACE dataset, Nerem and Wahr were able to conduct their experiment confirming the relationship between ice mass loss and the shape of Earth. But this Nerem says is only a starting point. "People have started to suggest that the melting in Greenland and Antarctica has started to affect Earth's rotation," Nerem said. "That is another thing to think about."
Using the GRACE values for ice loss in Greenland and Antarctica, Nerem and CIRES Fellow and physicist John Wahr, predicted how that ice loss has changed Earth's shape since 2002, and their calculations agreed with the changes recorded by laser-ranging measurements from a variety of different satellites.
"We found that Greenland and Antarctica cause most of this change," Nerem said.
The two regions are losing a combined 382 billion tons of ice a year, which means Earth's waistline is growing at about 0.7 centimeters per decade, Nerem said.
From the time scientists first began measuring Earth's shape, they've noted it's not a perfect sphere, Nerem said. The spinning of the planet means, just like any non-rigid spinning object, material tends to move out to the equator. "So there is more mass along the equator than there is at the poles," he said.
Most of the time the scientists have been taking measurements of its shape, Earth has been changing from this elliptical, or oblate shape, to a rounder one as it readjusts to the end of the ice age 20,000 years ago, Nerem said. Since the downward
By Jane Palmer
Like many of its denizens, Earth is getting thicker around its middle. But it is not cookies and donuts that pose a problem for the podgy planet, but an age-old slimming elixir: water.
Ice loss from the Greenland and Antarctica icesheets that injects the oceans with more fresh water drives the phenomenon, says CIRES Fellow and aerospace engineer Steve Nerem.
"If you imagine Earth is like a soccer ball and you push down on the North Pole it would bulge out at its 'equator'," he said. "So Earth ends up looking like a slightly squished ball."
The change in Earth's shape reflects the redistribution of mass on the planet and, as gravity depends on mass, Earth's gravity field changes also, Nerem said. Scientists can measure this variable from satellites. Data from the Gravity Recovery and Climate Experiment (GRACE)—twin satellites launched in 2002 that make detailed measurements of Earth's gravity field to monitor changes in ice mass, the amount of water in the ocean and losses in continental water—enabled the researchers to test a theory that the ice loss was changing the planet's shape.
