The point where the Pine Island and Thwaites glaciers meet the sea serve as a back-stop restraining most of the great ice flows of West Antarctica. If those backstops were to fail, ocean water would flood inland along a reverse slope and generate a massive and swift out-rush of ice that would ultimately raise the world’s oceans by about 3 meters. And, lately, the evidence is mounting that the backstops are failing.

At Thwaites, just south of the neighboring Pine Island Glacier (PIG), recent research found that the ocean was flooding inland beneath that enormous ice sheet at a rate of up to 400 meters per year. But to the north, there is indication of trouble at the ice surface.

Back to Back Calving Events

Just last September, a massive 100 square mile ice berg calved off the Pine Island Glacier. The event was significant in that it marked the first major retreat of the glacial front in the face of an advancing ocean. Pine Island had already sped up. But the calving face withdrawal inland appeared to mark a new phase for the large glacier.

Another calving event at Pine Island Glacier as seen by @Copernicus #sentinel1 as the rift as the SW ice shelf released multiple small icebergs. It will be interesting how the rest of this high damage area will react. pic.twitter.com/PxwLNoaF4w — Stef Lhermitte (@StefLhermitte) April 4, 2018

(Sentinel 1 satellite observations show a rapidly moving Pine Island Glacier calving off another large ice berg. Meanwhile, considerable damage appears to have been done to the glacial front.)

Now, just 7 months later, PIG is calving again. A large, approximately 6 kilometer long, 1 kilometer wide, chunk appears to have broken off into the Southern Ocean and shattered. Meanwhile, to the north and south along the glacial front, rifts appear to have formed.

This recent calving event is significant for a number of reasons. The first is that it’s happening just months after a recent large break-off during 2017. Other recent calving events at Pine Island occurred during 2001, 2007, and 2013. The present 2017-2018 events are back-to-back. The second reason is that the splintering appears to indicate a more fragile ice face. An impression reinforced by the concordant formation of rifts spreading away from the calving zone. The third is that the satellite imagery suggests Pine Island Glacier is moving quite rapidly (Recently, this rate of motion has been 1-2 km per year. However, it’s reasonable to question whether the glacier is continuing to speed up).

Conditions in Context

Present global warming due to fossil fuel burning has now forced the world into a range of temperatures between 1.0 and 1.21 degrees Celsius above 1880s averages. This boundary is similar to that of the lower range of the Eemian 120,000 years ago when oceans where 10-20 feet higher than they are today.

(The tall ice cliffs composing the Pine Island Glacial front have become increasingly fragile and fast moving as they enter the warming Southern Ocean and as that warming water continues to invade inland. Image source: Commons, Pine Island Glacier Calving Front, NASA.)

Under present greenhouse gas forcing and planned emissions, additional warming is in store. Climate models produced by Dr. Michael E Mann indicate that we are likely to hit the 1.5 C global temperature boundary some time between 2027 and 2031 on the current emissions pathway. This predicted warming is significant because analysis of past climates appears to indicate a risk of more rapid rates of sea level rise when global temperatures rise to a range between 1.5 to 2.5 C above past base line averages (see meltwater pulse 1 A).

Since the 1990s, the global rate of sea level rise has proceeded at roughly 3.3 mm per year with an apparent acceleration to around 3.6 to 4.1 mm per year during the 2010 to present time period. Given observed ice sheet instability in West Antarctica, in East Antartica, and in Greenland, there is a serious risk that this rate of rise will continue to accelerate over the coming years and decades. The key question of concern is how much and how soon.