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An Icy Dilemma
While the Earth's smaller glaciers are known to be shrinking rapidly, leading to an increase in sea level over the last few decades, less is known about the massive sheets of ice at the planet's poles.
Polar ice sheets in Greenland in the north and Antarctica in the south collect about three-tenths of an inch (eight millimeters) of the Earth's water every year. While that sounds like a miniscule amount, sea levels would drop three inches (eight centimeters) every decade if the water didn't trickle back into the oceans. Water melting from the edges of icebergs appears to make up for the loss, though researchers still don't know which is greater; the water going into the oceans, or that retreating into polar ice sheets.
This image is a view of the Greenland (left) and Antarctic (right) ice sheets as seen by NASA's Ice, Cloud and land Elevation Satellite (ICESat), which uses lasers to make precise measurements of elevation and surface features. The satellite shines its lasers down on Earth, then collects the reflected light in a one-meter telescope and calculates elevation by measuring the total time of each laser pulse.
ICESat flies in a near-polar orbit around Earth, giving it a clear look at Greenland and Antarctica. The satellite was launched on January 12, 2003, and its initial topographic measurements across Antarctica have already detected details such as the ice streams of the Siple Coast and the Amery Ice Shelf, and the atmospheric phenomena above them. ICESat researchers hope the instrument will help determine the extent to which polar ice sheets contribute to rising sea levels, which are increasing at a rate of almost an inch (two centimeters) per year.
CREDIT: NASA
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