|Iceberg Ross Sea, Antarctica. Photo © Bruce Luyendyk|
A few weeks ago I posted about discoveries that showed dynamic collapse of marine-based parts of the West Antarctic Ice Sheet is underway (May 20, 2014). What I want to explore now is the current thinking of scientists on the role of Antarctica in sea level change this century.
It will come as no surprise that sea level is projected to rise from the influence of global warming. This is discussed in both the Intergovernmental Panel on Climate Change (IPCC) AR5 report (Assessment Report Five 2013) and the 2014 National Climate Assessment. What do these reports say about sea level change and Antarctica’s role – and do the reports address the dynamic collapse scenarios revealed by studies published in the last few months?
First, “Projections suggest a substantial increase in 21st century Antarctic snowfall, mainly because a warmer atmosphere would be able to carry more moisture into polar regions. Regional changes in atmospheric circulation probably play a secondary role. For the whole of the Antarctic ice sheet, this process is projected to contribute between 0 and 70 mm to sea level fall [emphasis added].”
Second, “There are strong indications that enhanced outflow (primarily in West Antarctica) currently outweighs any increase in snow accumulation (mainly in East Antarctica), implying a tendency towards sea level rise.”
Third, “Before reliable projections of outflow over the 21st century can be made with greater confidence, models that simulate ice flow need to be improved,…”
Last, “Sea level could rise if the effects of marine instability [collapse of marine-based portions of the ice sheets] become important, but there is not enough evidence at present to unambiguously identify the precursor of such an unstable retreat.”