Study attributes Antarctic glacier melt to volcanoes

A recent study published in the Proceedings of the National Academy of Sciences presents strong evidence that geothermal heat from volcanic magma under the West Antarctic Ice Sheet (WAIS), not global warming, is a major factor contributing to glacial melting.

Using radar techniques to map water flows under the Thwaites Glacier in western Antarctica, researchers at the University of Texas Institute for Geophysics (UT-IG) found the resulting heat was much more widely and less evenly distributed than previously believed, with some areas considerably hotter than others. Thwaites, one of the world’s largest and most rapidly retreating glaciers, is of special interest for predicting sea level rise.

Getting a good handle on the relative influence of natural thermal conditions has proven to be very challenging. As the report states: “Geothermal flux is one of the most dynamically critical ice sheet boundary conditions, but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers.”

Yet as UT-IG lead researcher David Schroeder commented in a press release, “The combination of variable sub-glacial geothermal heat flow and the interacting sub-glacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined.”

Previous estimates depended extensively upon theoretical modeling. But as UT-IG report coauthor Don Blankenship observed, “It’s the most complex thermal environment you might imagine. And then you plop the most critical dynamically unstable ice sheet on planet Earth in the middle of this thing, and then you try to model it. It’s virtually impossible.”

Another WAIS glacier at Pine Island gained major attention when satellite measurements revealed it has retreated 19 miles since 2005.  A large iceberg that broke loose caused media-trumpeted speculation that this “race to the sea” heralded the beginning of the end for the West Antarctic Ice Sheet.

A subsequent satellite study reported in a 2000 issue of the Journal of Geophysical Research determined that the dynamics of ice thinning over the entire Pine Island drainage basin — which amounted to about 1.6 meters per year between 1992 and 1999 — was most likely driven by phenomena operating on time scales of hundreds to thousands of years, not by 20th Century warming.

And what net contribution to sea level rise will result if this thinning rate continues unabated? It will amount to about 6 mm — the width of a paper clip — each century.

There’s nothing new about concern regarding glacial melting causing sea level rise, a natural phenomenon that has been occurring over eons. After all, sea levels rapidly rose by as much as 130 meters as world ice sheets melted at the end of the last Ice Age about 13,000 years ago.

A 1922 article which appeared in a South Australia newspaper warned: “We are now, it is believed, slowly approaching another warm epoch, when, if it becomes universal, affecting both hemispheres together, the ice will again melt, and the sea rise to its ancient level, submerging an enormous portion of what is now dry and thickly populated land.”

As for dramatic shifts in the WAIS, there’s nothing new about that either. A major study released by the British Antarctic Survey (BAS) last year found that the Pine Island glacier thinned just as rapidly 8,000 years ago as it has in recent times, yet subsequently recovered.

Another BAS study published in the journal Geophysical Research Letters reported that WAIS thinning is “within the natural range of climate variability” over the past 300 years. It also noted that, “More dramatic isotopic warming (and cooling) trends occurred in the mid-19th and 18th Centuries,” suggesting that the anthropogenic (human-caused) climate influences in this location cannot be the driver.

Meanwhile, as the WAIS once again thins, Antarctic sea ice continues to grow and break recent records. At the end of May that extent reached the highest level recorded since satellite measurements first began in 1979. That expanse reached nearly 13 million square kilometers, beating the previous 2010 record of 12.7 million kilometers. The new record was 10.3% above the 1981-2010 climatological average of 11.7 million square kilometers.

Geological evidence suggests that the Antarctic coastline, which is now covered with ice,was ice-free only 6,000 years ago. Much more recently, in 1513, a Turkish sea captain named Piri Reis was able to chart open coastline waters, so that does not really tally with global warming (or cooling) as recent climate change events either.

Let’s finally realize that West Antarctic Ice Sheet has been melting at about its recent rate over thousands of years. This condition is expected to continue until either it entirely disappears, or until such time as the next Ice Age intervenes to stop it. Let’s hope that the latter circumstance doesn’t occur any time soon.