Tuesday, February 4, 2014

Less snow may cause the near term collapse of ice shelves in Antarctica

Sou | 1:02 AM Go to the first of 7 comments. Add a comment

There's a new paper out by scientists from Utrecht University and members of the British Antarctic Survey that looks at how the disappearance of the snow layer on top of ice shelves could be leading to their collapse. Here's an image from the paper to illustrate what happens:

Fig. 1. Conceptual illustration of firn air depletion and its consequences for ice-shelf hydrology and stability. (a) An ice shelf covered by a firn layer containing sufficient air. The inset shows meltwater being stored in the pore space of the firn. (b) An ice shelf with a depleted firn layer. Due to the absence of pore space, meltwater forms ponds that drain into fractures. Alternatively, water is routed to the fractures efficiently as shown in the leftmost fractures.
Source: Kuipers Munneke et al (2014)

From ScienceDaily.com

A number of floating ice shelves in Antarctica are at risk of disappearing entirely in the next 200 years, as global warming reduces their snow cover. Their collapse would enhance the discharge of ice into the oceans and increase the rate at which sea-level rises. A rapid reduction of greenhouse gas emissions could save a number of these ice shelves, researchers at Utrecht University and the British Antarctic Survey say in a new paper published today in the Journal of Glaciology.

Back in 1995 and 2002, two floating ice shelves in the north of the Antarctic Peninsula (Larsen A and B) suddenly collapsed -- each event occurred in a matter of weeks.

Dr Peter Kuipers Munneke, the paper's lead author, said: "This was a spectacular event, especially when you imagine the size of these ice shelves, which are several hundreds of metres thick, and have been in place for over 10,000 years."

The team of researchers suspected that the disappearance of the snow layer on top of the ice shelves could be an important precursor for shelf collapse. Their calculations confirm this hypothesis, and show that many more ice shelves could disappear in the next 200 years.

The scientists believed the snow layer plays an important role in regulating the effect of meltwater lakes on the ice shelves.

As long as the snow layer is sufficiently thick and cold, all meltwater can sink into the snow and refreeze. But in a warmer climate, the amount of meltwater increases, and the snow layers become thinner.

As a result, meltwater can no longer refreeze and forms large lakes on the surface of the ice shelves. The water drains through cracks and faults, causing them to widen until they become so wide and deep that the entire ice shelf disintegrates.

After their collapse, ice shelves can no longer provide resistance to the flow of the glaciers previously feeding them. As a result, the glacier flow accelerates significantly, contributing to an increase in sea-level rise.
The researchers performed calculations that show how this process may evolve over the next 200 years, using two different climate scenarios.

Dr Kuipers Munnekke said: "If we continue to burn fossil fuels at the current rate, almost all ice shelves in the Antarctic Peninsula will be under threat of collapse in the next 200 years. Only the two largest ones seem to be safe. Even in the much colder eastern part of Antarctica, some ice shelves could disintegrate. If we manage to keep global warming below the European Union target of 2oC, more than half of the ice shelves could be saved, compared to no action taken on emissions reductions."

The study received financial support from the European Union's four-year ice2sea project. Prof. David Vaughan said "We've been observing ice-shelf retreat around the Antarctic Peninsula since the early 1990s, but for the first time this model provides a strong basis for the prediction of future changes, which is a major step forward in understanding future sea-level changes."

Peter Kuipers Munneke, Stefan R.m. Ligtenberg, Michiel R. Van Den Broeke, David G. Vaughan. Firn air depletion as a precursor of Antarctic ice-shelf collapse. Journal of Glaciology, 2014; 60 (220): 205 DOI: 10.3189/2014JoG13J183


  1. As Hansen has been saying for years (eg. Hansen 2007) the dynamic response of ice sheets is being under-estimated. If we persist with BAU, we are in for a nasty surprise, or more correctly, a whole cascading sequence of them.

    Something that infuriates me is the way deniers will pick the lowest estimate for SLR at 2100 they can find and act as though that will be it. Magical halt. No more ice-sheet collapse. Completely failing to understand that once they start to go, no power on earth can stop them.

    This is a disturbing companion piece to Munnenke et al. BBC news article here.

    1. Indeed, there seems to be a general discrepancy between the relatively conservative model predictions, and the results from paleogeography. The obvious ones being the Eemian, where we get something like 6m higher sea levels with conditions little different from now, or more extreme the Pliocene, where levels are anything up to 27 meters higher, based on something like 2-3K over pre-industrial.

      If we carry on our current emissions track, global temperatures will exceed Pliocene levels by the end of the century, which means that we are gambling pretty much everything on the ice sheet response being slow.

      There is an interesting site http://flood.firetree.net/ where you can check the effects.

  2. I'm waiting to see what melt water does to the Greenland ice sheet, given the way that its surface melted last northern summer. Thermodynamics and even Newton would suggest that you don't melt that much ice without consequences...

  3. One thing that's always concerned me it the effect of rising sea level on the stability of ice shelves and ice sheets. It's pretty obvious that rising sea level will move the grounding line between the shelves and sheets back a bit. Then if the ice sheet melting speeds up because of that it causes a further rise in sea level which exacerbates the problem even more. It seems that could become a self driving feedback that could be difficult to control.

    1. Yes, this is a known risk. It's a problem mostly for marine-based ice sheets, including parts of Greenland, most of West Antarctica, and sections of East Antarctica. Doesn't matter much for ice that enters the ocean already above sea level.

    2. Och erm.........


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