A new study indicates that the West Antarctic Ice Sheet is in a state of irreversible decline. Over the past 40 years, the flow of glaciers into the sea has sped up. As a result, the sheets are thinning, melting the ice faster than we thought it would. Soon, sea levels will be rising.
As the ice flows into the sea, it melts faster where it contacts the seawater. As more ice melts, the sheets are lighter. This makes it float easier, with seawater creeping under to expose yet more of the sheet to increased melting. This is called grounding line retreat, and it's a key component in creating a positive feedback loop of melting.
Grounding line retreat is when a lighter glacier floats more easily, increasing melting. Image credit: NASA/JPL
Now the sheet is floating in places it used to be in solid contact with the bedrock, melting faster, getting lighter, and floating higher. It's a horrible positive feedback loop that is driving faster melting of the sheet. And it's going to keep getting worse.
Eric Rignot, researcher at UC Irvine and NASA's Jet Propulsion Laboratory, explains:
"The collapse of this sector of West Antarctica appears to be unstoppable. The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers. At this point, the end of this sector appears to be inevitable."
"Collapse" is a technical term in science. It sounds like an immediate, dramatic catastrophe, but in reality it's a slow, gradual crumble of ice that is easy to ignore without careful monitoring. The only way this backwards climb of the grounding line and rapid melting of the ice sheet is going to stop is if the bedrock has a pinning-point, a small rise to keep the glaciers from slipping seawards. From ice radar mapping the under-ice topography, we aren't seeing any pinning points in five of the six glaciers. And that sixth glacier? It's retreating just as fast as the others. When this ice melts, it will dump enough water in the oceans to raise sea levels by over a meter.
This leaves me painfully depressed. As a geoscientist, I guess I can be excited that whole new stretches of previously-inaccessible bedrock are going to become gorgeous exposures for geological mapping in the near future, but that's not much of a consolation prize.Goodbye, West Antarctic ice sheet. You were astonishing while you lasted. Are we done debating climate change yet?