Two new papers published this week suggest that the West Antarctic glaciers draining into the Amundsen Sea — the Pine Island, Thwaites, Haynes, Pope, Smith and Kohler glaciers — are melting rapidly and are now committed to collapse, adding up to 1.2 metres to future sea level rise. In the NASA JPL video above, Eric Rignot, lead author of a paper ((E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl. Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011. Geophysical Research Letters, 2014; DOI: 10.1002/2014GL060140)) examining how the glaciers’ “grounding lines” — the point where the bottom of the glacial ice leaves the bedrock and starts to float — have retreated very significantly over the last 20 years explains how they are now melting back unstoppably. Another paper modelling ice loss from the Thwaites glacier ((Ian Joughin, Benjamin E. Smith, Brooke Medley. Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Science, DOI: 10.1126/science.1249055.)) finds that it is committed to retreat and collapse via the same mechanism. Lead author Ian Joughin of the University of Washington, told Science magazine:
The next stable state for the West Antarctic Ice Sheet might be no ice sheet at all…
That would add over 3 metres to future sea level, although Joughin et al find that Thwaites collapse is likely some way off in the future. Their paper concludes:
Nonetheless, the similarity between our highest melt rates and present observations suggests that collapse may be closer to a few centuries than to a millennium.
Rignot told Science that more realistic ocean modelling of the ocean’s effects on Thwaites could bring the date of collapse closer to the present.
Glaciologist Richard Alley told the New York Times that news of the two papers findings “shook me a little bit”:
“If we have indeed lit the fuse on West Antarctica, it’s very hard to imagine putting the fuse out,” Dr. Alley said. “But there’s a bunch more fuses, and there’s a bunch more matches, and we have a decision now: Do we light those?”
Rignot provides a more detailed explanation of the melting process in this video, also well worth watching:
The stability of the West Antarctic ice sheet has concerned scientists since the 1970s. There are multiple lines of evidence that it has collapsed in whole or in part during the last (Eemian) interglacial (LIG), and may have done so rapidly — on a timescale of decades to centuries. It now looks very likely that the processes that will lead to another collapse are well under way. There is a very real risk that they will continue whatever we do to restrain climate warming. We know from the LIG that sea levels were as much as 9m above present by the end of that warm period — with CO2 100 ppm lower than present.
The bottom line is clear: even if the global community succeeds in hitting a 2ºC target and the atmosphere stays under 450 ppm CO2 , we are going to have to say goodbye to the current coastline and everything built there. The long transition has begun in earnest. We can but hope that it is a process slow enough to allow us to adapt.