What's driving Antarctica's meltdown?

A satellite image shows Antarctica's Byrd Glacier flowing into the Ross Ice Shelf. The continent's ice shelves are critical for slowing the flow of land ice into the ocean. Credit: Jesse Allen/NASA

From Inside Climate News:

The floating ice shelves along the edges of West Antarctica that slow the flow of its vast glaciers are under assault from all directions, and they're becoming more vulnerable to collapse, scientists warn.

Warmer water has started creeping in under them, eating away at the ice from below. Warmer air—and, in places, more rain—is melting the surface, creating ponds that can drain deep down and then splinter ice from within.

Now, new research is highlighting another threat: Since 2000, moist and warm tendrils of air known as atmospheric rivers have been swirling toward the coast more frequently, bringing more rain and surface melting.

Antarctica has been losing about 250 billion tons of ice annually in recent years, and research shows the rate has increased sixfold since 1979. At this pace, researchers have suggested, West Antarctica's ice shelves may reach climate tipping points and crumble, sending sea level rise surging well beyond current projections.

The floating ice shelves, partly frozen to the sea floor or to fjord walls, hold back vast quantities of land-based ice that could raise sea level more than currently projected if the ice's flow to the sea speeds up, said Penn State climate researcher Richard Alley.

Alley noted that some research has suggested that, if global warming pushes West Antarctica's towering ice cliffs to collapse, it could raise sea level more than 3 feet by 2100, surging to 50 feet by 2500, from Antarctic ice melt alone.

"That model is sometimes treated as a worst-case scenario, but in fact the model used a maximum calving rate that has briefly been exceeded in Greenland already, and the possibility exists that even faster calving could occur from higher, wider cliffs that could develop in Antarctica," he said.

Even the most recent international assessment of ice loss relies on models that don't account for some of those ice shelf tipping points, he said. "If we're fortunate, and the ice shelves are retained, then these models may be accurate. If we do lose the ice shelves, the models may project less sea level rise than will occur, perhaps by a lot."

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