Could Gravity Save Antarctic Ice?

Maybe, maybe not, but a new study argues climatologists—and policymakers—need to start taking geophysics into account.
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A satellite composite image of Antarctica. (Photo: Wikimedia Commons)

A satellite composite image of Antarctica. (Photo: Wikimedia Commons)

Climate scientists know that as the world warms, sea levels will rise and coastlines will change. But those scientists may need to adjust their estimates of where and how big those changes will be. According to a new study, factors like the malleability of the Earth's crust and the gravitational pull of the Antarctic Ice Sheet are likely to have a substantial impact.

The Antarctic Ice Sheet has been in the news a fair amount lately, mainly because quite a bit of it is melting away. In fact, scientists have grown adept at identifying not just how much ice is melting, but also where it's melting—and, complicating matters, where the ice is actually building up.

What the scientists haven't done—at least not in much detail—is figure out where that water will go. For that, write researchers Natalya Gomez, David Pollard, and David Holland, you need to understand that our planet isn't the uniform, rigid sphere we usually imagine; its mountains compress the crust underneath and create subtle variations in the force of gravity, which researchers have been able to detect since the late 19th century.

"We need to incorporate these sea-level effects into ice sheet models in order to refine projections of future ice loss."

Ice sheets are no different, Gomez and her colleagues explain. That might well sound absurd, but at a mile thick and a few thousand miles across, the AIS contains somewhere around 30,000 trillion metric tons of water—plenty enough gravitational pull to lift the surrounding waters above the global ocean average, and enough weight to flatten out the South Pole. (Indeed, scientists measure how much ice the sheet's losing in part by tracking how much higher the land gets every year.)

What all that means is that, as the AIS melts, the land underneath it will rise and the AIS's gravitational pull on the surrounding waters will decline, resulting in a lower sea level near the coasts of Antarctica. As that happens, the AIS will rise out of the water. But one of the main reasons the AIS is melting is because of contact with seawater, so as the sea recedes, the ice sheet will melt more slowly. In other words, the AIS might stick around longer—and the world's oceans might rise less quickly—than previously thought. Depending on how much the Earth warms up, that could be enough to prevent, or at least delay, the complete collapse of the western reaches of the AIS, the team writes.

But that's not to say the future is bright. More to the point, "we need to incorporate these sea-level effects into ice sheet models in order to refine projections of future ice loss," Gomez writes in an email. "Sea-level changes have a stabilizing influence on the ice-sheet retreat and have the potential to slow or stop retreat in the future, so this is good news from a sea-level hazard perspective. But as recent research has been highlighting, there are a number of other factors that will influence the ice-sheet retreat."

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