Will Antarctica shrink or grow as climate warms?
Antarctica from space. Satellite data from 2002 to 2005 showed a loss of ice overall, but this trend might not continue.
DB: This is Earth & Sky, on what’s happening on the far southern continent of Antarctica as Earth gets warmer.
JB: Antarctica is completely surrounded by an ocean. As this southern ocean warms, more water evaporates from the sea surface. That evaporating sea water increases snowfall over the southern continent.
DB: On the other hand, the warming ocean also causes ice near the edges of the Antarctic continent to slide more rapidly into the sea, causing sea level to rise.
John Wahr: And it turns out that those two things are in pretty close balance . . .
JB: That’s John Wahr, University of Colorado geophysicist.
John Wahr: And suppose something comes along to just affect one of those numbers a little bit. Say it increases the discharge into the ocean by, I don’t know, 10 percent. If you just tweak one of them a little bit, that one can win. It can have big effects on sea level.
JB: Antarctica’s ice has the potential to have a huge effect on the rising level of Earth’s oceans. For their part, Wahr and his colleagues used satellite data to learn that, from 2002 to 2005, Antarctica lost more water to the ocean than it gained from precipitation.
DB: Wahr and other scientists are continuing to monitor the southernmost continent, hoping to help predict how much the sea will rise in this century. More at earthsky.org.
JB: Our thanks today to NASA. We’re Block and Byrd for Earth & Sky.
The report by John Wahr and his colleague Isabella Velicogna was published online by the journal Science, at the Science Express website, on 2 March, 2006. Read the abstract here.
They found that each year between 2002 and 2005, Antarctica contributed about half a millimeter – or a little more than a tenth of an inch – to sea level rise. Another way to look at it is that Antarctica lost about 36 cubic miles of water each year. That?s about as much water as the city of Los Angeles uses in 36 years.
Wahr says this is the first time that anyone has been able to measure the ice mass of the entire Antarctic continent.
Wahr and Velicogna used the twin satellites of GRACE (the Gravity Recovery and Climate Experiment) to measure Antarctica?s total ice mass.
The two satellites orbit Earth together, one following the other. They precisely measure the distance between each other. As the first one approaches an area on the surface of higher mass, say the continent of Antarctica, it speeds up slightly. And as it passes Antarctica, it slows down slightly. This slightly changes the distance between the two satellites. Laser beams sent between them measure their separation with high precision. That changing distance is then translated into mass below.
See an animation of the GRACE satellites in orbit.
Wahr says that the GRACE satellites should continue operating for another 7 years.
Our thanks to:
John Wahr
Geophysicist
University of Colorado
Boulder, CO
Additional Teacher Resources
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