Tuesday, May 20, 2014

Antarctic Ice Sheets – the fuse has been lit.

snowmobile and sledge cross blue ice on Balchen Glacier, Marie Byrd Land. Photo © Bruce Luyendyk
Snowmobile party crossing blue ice of Balchen Glacier, 
Marie Byrd Land, West Antarctica. Photo © Bruce Luyendyk

Have the Antarctic Ice Sheets reached the Point of No Return? My last entry was an excerpt from my memoir about flying past the Point of No Return (AKA Point of Safe Return) in route from Christchurch to McMurdo Station, Antarctica. This entry is about an entirely different PNR, that 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 PNR for stability of the ice sheet has been passed.

The WAIS covers the subcontinent of West Antarctica in thousands of feet of ice.
About the area of Mexico, if the WAIS melted entirely sea level would rise an average three meters around the world (ten feet).
WAIS stability means that the ice is not melting faster than it is forming and is not causing global sea level to rise. Scientists have found that this is not the case. The WAIS is now unstable and melting at a rate beyond the rate it can be replaced. Neither can the melting be slowed or stopped. The PNR has been past.

The new evidence is from two separate investigations. In one study satellite radar observations over twenty years detected many kilometers of 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 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 is capable of raising 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 holds back a large portion of the EAIS from entering the sea. This means parts of the EAIS are also susceptible to similar factors causing retreat of the WAIS.

What is the culprit? It’s global warming of course, but not the warming of the air around Antarctica. Rather it is the warming of the ocean that is melting the ice sheets from below and removing 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 for 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 rate of melting of the ice sheets and their contribution to global sea level rise will be larger than previously thought.

What does this all mean? Short answer, that the Earth’s large ice sheets are more fragile than we thought. Increased amounts of 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 melting of mountain glaciers. Now more is known about the contributions and risks of ice sheets melting.

The Intergovernmental Panel on Climate Change (IPCC; http://www.ipcc.ch ) estimates about half a meter of 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. The sea will encroach up the beach anywhere from 30 to 100 feet farther depending on the slope. The effect is clear - coastline retreat. In regions of the world where the coastal plains have almost no slope, vast areas of land will be inundated and inhabitants displaced.

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

In a NY Times piece on May 12 Professor Richard Alley of Penn State was asked to react to the new findings from West Antarctica.
 “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?”

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