Rate of Ice Cap Loss May be Slower than Feared: New Study


Photo Credit: christine zenino via Flickr/CC BY

A new study published in the scientific journal Nature Geoscience suggests that the estimates for the rate of ice loss in Greenland and West Antarctica from global climate change should be significantly reduced -- by as much as half. The study posits that current ice loss estimates fail to take into account a process called glacial isostatic adjustment, which involves the rebounding movement of the Earth's crust after the last ice age. Here's what's happening, according to NASA scientists. Scientists from NASA's Jet Propulsion Laboratory and the Delft University of Technology in the Netherlands recently employed a new method (which is explained here) for measuring "trends in how water is transported across Earth's surface and how the solid Earth responds to the retreat of glaciers following the last major Ice Age".

In an interview with the Agence France-Presse, the lead researcher Bert Vermeersen of Delft Technical University, explained what they learned is happening to the Earth's crust: "A good analogy is that it's like a mattress after someone has been sleeping on it all night," he said. The AFP explains further:

The weight of the sleeper creates a hollow as the material compress downwards and outwards. When the person gets up, the mattress starts to recover. This movement, seen in close-up, is both upwards and downwards and also sideways, too, as the decompressed material expands outwards and pulls on adjacent stuffing.

Often ignored or considered a minor factor in previous research, post-glacial rebound turns out to be important, says the paper. It looks at tiny changes in Earth's gravitational field provided by two satellites since 2002, from GPS measurements on land, and from figures for sea floor pressure. These revealed, among other things, that southern Greenland is in fact subsiding, as the crust beneath it is pulled by the post-glacial rebound from northern America.

Interesting stuff -- but what of the implications for climate change and the rate of ice cap loss at the poles? NASA explains:
the researchers ... calculated new estimates of ice loss in Greenland and Antarctica that are significantly smaller than previous estimates. According to the team's estimates, mass losses between 2002 and 2008 measured 104 (plus or minus 23) gigatonnes a year in Greenland, 101 (plus or minus 23) gigatonnes a year in Alaska/Yukon, and 64 (plus or minus 32) gigatonnes a year in West Antarctica. A gigatonne is one billion metric tons, or more than 2.2 trillion pounds. The smaller but significant ice loss estimates reflect the revised role that post-glacial rebound was found to play in relation to current ice mass loss in Greenland and Antarctica.
Note that there is still a phenomenal rate of ice loss at the poles: Greenland and Alaska are still shedding over 100 billion tons of ice a year by the new estimates. And the general rate of sea level rise is thought to be unaffected, which potentially means that more of the rise should be attributed to thermal expansion -- how sea levels rise as it warms.

Finally, the paper does not challenge any of the basic mechanics of anthropogenic climate change -- and further review is necessary to confirm its claims. But even if it turns out to be right on, it the data might mean that something like thermal expansion is more of a problem than previously thought.

More on Polar Ice Loss
Arctic Sea Ice Loss Confirmed As Main Cause of Faster Polar Melt
Greenland Ice Cover Loss Shown with New Earth-Space Monitoring System (Video)

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