The “Unstoppable Collapse” of the West Antarctic ice sheet – the rest of the story

The mainstream media and the Arizona Daily Star are in their usual “gloom and doom” mode because a few glaciers in the Amundsen Sea of West Antarctica are flowing faster than they have been and hence calving ice into the sea. This glacial behavior has been known for some time. The current turmoil was precipitated by recent publication of two papers based on data collected between 1992 and 2011.  But even back in 1968, a paper by Ohio State University glaciologist John Mercer called the West Antarctic Ice Sheet a “uniquely vulnerable and unstable body of ice.” Mercer based his statement on geologic evidence that West Antarctica’s ice had changed considerably many, many millennia ago at times when the ice sheets of East Antarctica and Greenland had not.

Is it just coincidence that this story is being hyped now, closely following release of the latest National Climate Assessment Report by the Obama administration? Is this just an attempt at “climate diversion” away from other issues? (See: National Climate Assessment Report = Science Fiction and Politics). Anthony Watts has some comments and links to the science on his WUWT blog.

I have yet to see any of the mainstream media mention the fact that Antarctic sea ice is currently at or near an all-time high extent (see article here).

The “gloom and doom” part of the “collapse” story is speculation that glacial calving will cause an undue rise in sea level. Studies show, however, that this “unstoppable collapse” will take hundreds to thousands of years and might possibly cause a sea level rise of 1.5 feet per century. Does that worry you?

To put things in perspective, let’s look at some geography and geology.

First is a NASA illustration of the offending glaciers (colored red):

Glaciers of Amundsen Sea Antarctica

For me, that illustration does not give a good sense of how much area we are taking about, so here is a more general map. Compare the tiny area of the Amundsen Sea sector with the total of Antarctica, or even with the total of West Antarctica:

antarctica_amundsen_sea_sector-1

 

In the scheme of things, this is a very small area of West Antarctica that is “collapsing.”

I have some questions about the net effect of all this on sea level rise.

Glaciers move usually because more weight, i.e., snow, is piled onto the upper parts of the glacier and gravity causes it to flow. Were does the snow come from? Evaporation from the ocean which reduces sea level.

In West Antarctica, the glaciers are “grounded” below sea level and are therefore displacing ocean water. Since water as ice has more volume per weight than liquid water, melting of “grounded” ice should also decrease sea level.

Another NASA illustration shows that the bedrock in the entire area covered by these glaciers (brown in the illustration below) is below sea level.

West Antarctica bedrock  topography

 

Floating ice already displaces its weight with an equal weight of water so the net effective on sea level of melting floating ice is near zero (Archimedes’ principle).

Only ice/snow that was always above sea level could raise sea level once it melted into the sea. How much is that compared to the evaporated water which produced the ice/snow on the upper parts of the glacier in the first place? What is the mass balance?

The website www.antarcticglaciers.org discusses the mass balance of Antarctic ice in great detail.

Here is their illustration of what is going on; note that they show a below-sea-level basin that is being melted:

 Antarctica Pine island glacier

As to my question on mass balance, Antarcticglaciers predicts:

“Climate models predict that, for a generally warmer climate, snowfall will increase over Antarctica. Surface melt will increase around the more northerly Antarctic Peninsula, and dynamic changes such as increased ice discharge, ice-shelf collapse and grounding line recession, and marine ice-sheet instability are likely to offset any increases in precipitation. However, if no dynamical ice response is assumed, then increases in snowfall over the entire continent of 6-16% to 2100 AD and 8-25% to 2200 AD are likely to result in a drop in sea level of 20-43 mm in 2100 and 73-163 in 2200, compared with today. However, it is more likely that the Greenland and Antarctic ice sheets will lose mass over the next century, with rapid coastal changes, increases in ice flow and ice-shelf collapse all likely. As a result of these complex expected changes, there are a number of uncertainties in past, present and future ice sheet mass balance.” (Emphasis added)

There is a great deal of uncertainty and the story will take several hundred to a thousand years to play out.

Ironically, the UN IPCC AR5 report says ““Projections of Antarctic SMB changes over the 21st century thus indicate a negative contribution to sea level because of the projected widespread increase in snowfall associated with warming air temperatures.” (Krinner et al., 2007; Uotila et al., 2007; Bracegirdle et al., 2008).” (13.4.4.1). So much for media hype.

END

A version of this post first appeared in the Arizona Daily Independent.

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