As David Spratt posted at Climate Code Red a giant crack has opened across the full width of the Pine Island Glacier (PIG) ice shelf, spawning a new iceberg about 720 square kilometres in area, roughly eight times the size of Manhattan Island in New York. This is about the best photo I can find:
We’ll get some orientation first and then look at the implications. This image locates the PIG on the continent of Antarctica:
This image from the LiveScience photo gallery outlines the PIG basin:
This basin together with the Thwaites Basin just to the south drains 40% of West Antarctica. These two glaciers alone could lead to sea level rise of half a metre by 2100 according to material cited by Spratt.
This image compares Antarctica with Greenland:
The red patches show the ice sheet thinning from 2003 to 2007.
This image shows the decadal warming from 1957 to 2007 as much greater in West Antarctica than on the giant ice sheet of East Antarctica:
David Spratt cites research and climatologists suggesting that the PIG and Thwaites glaciers may have already tipped. He reckons that Fred Pearce’s prediction made some years ago looks spot on:
Another vulnerable place on the West Antarctic ice sheet is Pine Island Bay, where two large glaciers, Pine Island and Thwaites, drain about 40 per cent of the ice sheet into the sea. The glaciers are responding to rapid melting of their ice shelves and their rate of ﬂ ow has doubled, whilst the rate of mass loss of ice from their catchment has now tripled. NASA glaciologist Eric Rignot has studied the Pine Island glacier, and his work has led climate writer Fred Pearce to conclude that ‘the glacier is primed for runaway destruction’. Pearce also notes the work of Terry Hughes of the University of Maine, who says that the collapse of the Pine Island and Thwaites glaciers — already the biggest causes of global sea-level rises — could destabilise the whole of the West Antarctic ice sheet. Pearce is also swayed by geologist Richard Alley, who says there is ‘a possibility that the West Antarctic ice sheet could collapse and raise sea levels by 6 yards [5.5 metres]’, this century.
As against that a recent study which attempts to come to terms with ice sheet decay suggests sea level rise of 69cm by 2100 with only a 5% chance that it could go beyond 84cm. That was in May this year. In June another study surveyed all the Antarctica ice shelves and found that the ‘basal melt’ the melting from below exceeded glacier flow and iceberg calving above. They found:
the melting underneath all of the ice shelves accounted for 55 percent of all ice-shelf mass loss between 2003 and 2008, which is significantly higher than what anyone had previously thought.
Spratt also cites research by Blancon et al which found that sea levels rose 3 metres in 50 years due to the rapid melting of ice sheets during the Eemiam interglacial 120,000 years ago. I’m cognisant of the fact that much of the bedrock under the Antarctic ice sheet is below sea level, bringing the ice sheet edges in direct contact. This is one image indicating the underlying topography:
Sea level is where blue and green meet. The intervals on the left are 5,000 feet (1,524 metres). Finally from the earlier post on Greenland I’ll repeat the image from James Hansen showing the effect that a 10-year exponential doubling of ice sheet melting can have late in this century:
I’d suggest that we still can’t be at all confident we know what’s going to happen by century’s end. Reality will be less smooth than Hansen’s lines. Chunks falling off the Pine Island Glacier are definitely a worry, but not so much immediately. The second half of this century is likely to see more dramatic action than the first.