Antarctic Shelf-Ice More Stable Than Thought: Potsdam Alarm Stories Becoming Obselete
By Dr. Sebastain Lüning and Prof. Fritz Vahrenholt
(Translated/edited with permission by P. Gosselin)
The Antarctic ice shelf is made up of huge ice sheets that float on the ocean and are firmly connected to the mainland ice cap. There are two main ice shelves: the Ronne-Filchner and Ross (Figure 1). There are also a number of other smaller shelves.
The ice shelves act as a block that holds back and brakes the mainland ice sheets. Just how well is this safety block functioning today? Do we have to worry that the Antarctic ice sheet will soon slide into the ocean and cause a sea level surge?
Such a horror scenario was spread to the public by climate scientist Anders Levermann of the Potsdam Institute for Climate Impact Research (PIK) four years ago. In a blog article at the PIK-friendly Klimalounge-Blog, Rahmstorf’s institute fellow colleague suggested dramatic consequences for the Antarctic shelf ice should a fundamental shift in global energy supply not rapidly take place. Levermann is also very closely associated with the IPCC and is a lead author of the current climate assessment report. In a recent article titled: “Untenable ice shelf – Updated“ he upped the stakes and added:
Simulations of the Antarctic here are briefly introduced. These show that the loss of the Ross Ice shelf 3 million years ago led to the collapse of the West Antarctic ice sheet and a seven-meter rise in sea level. […] to make statements with certainty on whether the retreat of the ice shelf is accelerating, the current data sets are not sufficient.”
According to theoretical simulations, the shelf ice is expected to disappear. Levermann does admit, however, that these models cannot be compared to hard measured data. Within the scope of the PIK ice shelf catastrophe publicity campaigns, a PIK Phd candidate was sent in to do an interview with the evangelical online magazine Chrismon, in which she made some surprising statements:
Climate change: The ice is sliding into the sea. In ten years… the Earth will be much warmer than today, climate scientist Maria Martin claims. She can prove this with the help of computer models.
CHRISMON: Has it gotten warmer in Antarctica?
MARTIN: We can assume this, also when the directly measured data in Antarctica do not go back very far. In 2002 a large ice shelf collapsed, it simply fell apart. We suspect this because melt water had formed there.”
Computer models as proof? That’s an adventurous claim. Even the IPCC reminds us that computer models only depict scenarios and can never be used as proof. Not a good start.
Then comes her next gaffe: Has it gotten warmer in Antarctica? Martin answers yes to this, but with a reference to supposedly limited measured temperature data, leaving a back door open. Let’s take a look at this supposedly “limited measured data” (Figure 2). According to RSS satellite data, it has gotten a bit colder, and not warmer, in Antarctica since measurements began in 1979. Obviously the PIK scientist is quite wrong with her suspicions. Her concluding reference to a past ice-shelf break is not exactly enlightening. Such calving is part of the transport conveyor that carries snow that was converted to ice in the interior of the seventh continent and on over to the coast. The ice shelf collapse she mentions has about as much informational value as a spilled sack of rice in China.
Figure 2: Temperature development since 1979 from RSS satellite data (lower curve). The upper curve depicts the development in the Arctic. Source: climate4you.
The final statement of the Potsdam ice shelf catastrophe campaign was made on 11 May 2013 at the online Neuen Potsdamer Nachrichten (PNN) [New Potsdam News]. Read it for yourself:
Chain reaction in Antarctica is feared Already in this century a gigantic ice slide threatens to occur in the Antarctic region, which up to now has played hardly a role in climate change. This is the conclusion that German scientists have reached with two simultaneous computer simulations. Unlike what was assumed, climate change also impacts the Weddell Sea, the largest shelf sea of the Southern Ocean on the Antarctic continent, scientists report in the journal ‘Nature‘. The warm water masses are having a massive impact on the Filchner-Ronne ice shelf. […] The giant ice sheet will soon begin to rapidly melt and disappear by the end of the century, the two scientists write with respect to their calculation. As a consequence, great amounts of mainland ice could slip into the ocean because shelf ice acting as a barrier would be lacking. This in turn would lead to a rise in sea level. ‘ Shelf ice is to mainland ice what a cork is to a bottle,’ explains AWI oceanographer and lead author of the study, Hartmut Hellmer. ‘They brake the flow of ice because they get snarled up everywhere in the bays and, for example, they get lodged on islands.
Also a second study published in ‘Nature Geoscience’ points to such a development. Scientists led by Martin Siegert of the British University of Edinburgh analyzed the thickness of two ice flows that feed into the Filchner-Ronne ice shelf using Georadar (Radio Echo Sounding, RES) – and the ground properties underneath. According to the analysis, there is a large steeply inclined basin with a smooth base that would hardly be able to counter a slip-away. The melt rate will increase from 5 meters per year today to up to 50 meters per year by the end of the century, so estimates AWI oceanographer Jürgen Determann. How the mainland ice would react to the mega-melting ice shelf is still open. However the scientists assume that it moves and that it will slide increasingly faster. Should the melting ice be completely offset by the subsequently flowing mainland ice, this would lead to an additional sea level rise of 4.4 millimeters per year.”
Other media outlets gratefully jumped on the story, such as the Augsburger Allgemeine and Spiegel. Yet, in the meantime, things have quieted down with regards to the Antarctic ice shelf catastrophe. For some reason the PIK and its associated institutes have lost their desire for the subject. What happened?
Hardly a month had passed since the Potsdam campaign ended before the first scientists appeared in public with very inconvenient words. A team of scientists led by Tore Hattermann of the Norwegian Polar Institute published a study showing gross errors made in the theoretical ice shelf models used. Hattermann and his colleagues set up a 12-tonne drilling rig on the surface of the Antarctic Fimbul ice shelf and bored through the more than 200 meter thick ice sheet at three locations. Underneath the ice they measured the temperature and produced a data set that was unique in its kind. Here they found surprising results: The ice shelf models had assumed a much too high temperature underneath the ice. In reality the water beneath the shelf ice was considerably colder. The mass loss postulated by the models could no longer be supported in the face of the new hard temperature calibration data. Moreover, the ice mass of the ice sheet currently appears to be hardly changing, as the team led by Hattermann was able to show in a paper in the Geophysical Research Letters.
Then just a few weeks later, things got a lot worse for the Potsdam scientists: In September 2012 a study in the journal The Cryosphere was published by a team of researchers of the University of California Irvine led by Bernd Scheuchl. Here the scientists compared radar measurements of the Antarctic Ross and Ronne ice shelves from 1997 and from 2009. Here the scientists determined the changes in ice shelf’s ice flow speed over the 12-year period. Both the large Mercer and Whillans ice flows of the Ross ice shelf had slowed by 50 m/year and 100 m/year respectively. Also most ice flows that feed into the Filchner-Ronne ice shelf show a moderate slowdown.
The results simply are not cooperating at all with the postulated Potsdam Antarctic shelf ice catastrophe.
Now just out is yet another paper that has been in print since the end of June 2013: Earth and Planetary Science Letters. An international team led by Christina Hulbe of the University of Otago in New Zealand extended the study even further back into the past. Using surface speed measurements from the 1970s and moderate-resolution imaging spectroradiometer (MODIS) from the 2000s, Christina Hulbe and colleagues were able to show that the biggest portion of the Ross ice shelf had slowed down in its movement during the last 30 years.
In Potsdam they reacted by switching the focus over to Indian monsoons. This will get them the media’s attention for a couple of months – at least until serious scientists take a closer, more serious look at the basis of their newest alarm story.
Dr. Sebastian Lüning and Prof. Fritz Vahrenholt are the authors of the new book: The Neglected Sun.