Antarctic Ice Sheets – the fuse has been lit.

Snowmobile party crossing the blue ice of Balchen Glacier, Marie Byrd Land, West Antarctica. Photo © Bruce Luyendyk

Have the Antarctic Ice Sheets reached the Point of No Return?

This blog is about where the stability of the West Antarctic Ice Sheet (WAIS) is lost. Two research studies published in the last few weeks have confirmed what has been feared; the Point of No Return for the ice sheet’s stability has been passed.

The new evidence is from two separate investigations.

In one study, satellite radar observations over twenty years detected many kilometers of the retreat of glaciers (the grounding line) in a major outlet region of West Antarctica that borders the Pacific Ocean (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract).  A second study used observations of the ocean under one of these glaciers, the Thwaites. The research found a melt rate that indicates the early-stage retreat of WAIS has begun (http://www.sciencemag.org/content/344/6185/735.abstract). The authors calculate that the collapse rate could reach a maximum in as soon as 200 years. The drainage area under study can raise the sea level by about four feet should it empty of ice.

Meanwhile, another study of the East Antarctic Ice Sheet (EAIS) along the coast facing Australia found that the geometry of the ice sheet there and the bed it rests upon is similar to that in West Antarctica (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2226.html). An ice dam on a submarine ridge prevents much of the EAIS from entering the sea. This means parts of the EAIS are also susceptible to similar factors causing the retreat of the WAIS.

What is the culprit? It’s global warming, but not the air warming around Antarctica. Rather it is the warming of the ocean that is melting the ice sheets from below and removing the ice mass that holds large portions of them in place. The warming of the ocean is the result of global warming.

Along with these new findings for Antarctica, the story of the Greenland Ice Sheet is equally troubling.

New research just published (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2167.html) found that here too, the ice sheet is sensitive to warming by the ocean from below – just like in portions of Antarctica. As a result, the ice sheets’ melting rate and their contribution to global sea-level rise will be larger than previously thought.

What does this all mean? The short answer is that the Earth’s large ice sheets are more fragile than we thought. Increased melting of them will contribute to sea-level rise this century and beyond. Other contributors to sea-level rise have been studied fairly well – the expansion of the ocean due to heating from the warmer atmosphere and the melting mountain glaciers. Now more is known about the contributions and risks of ice sheets melting.

About half a meter of sea level rise is predicted by 2050 (about 1 ½ feet)

The Intergovernmental Panel on Climate Change (IPCC; http://www.ipcc.ch) estimates about half a meter sea level rise by 2050 (about 1 ½ feet). Why is this a problem? Stand on any beach, even one on a lake. Notice the slope of the beach, how gentle it is. Imagine a permanent high tide about 1 ½ feet higher than now. Depending on the slope, the sea will encroach up the beach 30 to 100 feet farther. The effect is clear – coastline retreat. In regions where the coastal plains have almost no slope, vast land areas will be inundated and inhabitants displaced.

What can be done? What will be done? When will it be done?

 “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?”