Weatherdem's Weblog

Bridging climate science, citizens, and policy


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Pine Island Glacier Past A Tipping Point?

A major glacier located in West Antarctica could, according to recent research, be near or past a tipping point, beyond which the glacier will inevitably slide into the ocean.  Pine Island Glacier has had its grounding line, the area where the glacier rests either on the ocean or land, pushed back toward land due to increasingly warm ocean temperatures melting it from below.  If it retreats behind a lip on the continental shelf, rapid and irreversible loss of ice will occur.

Investigation into the glacier indicates that the grounding line may have retreated behind the lip back in 1996.

Research indicates that before the next stable grounding line can be reached on the inner slope, half of the land-based glacier will have melted into the ocean.  Melting land-based glaciers result in rising sea levels.  Half of Pine Island Glacier would raise sea levels by 9″ before 2100.  If a nearby glacier also retreats, sea levels would rise by 20″.  Either case would result in the displacement of millions of people worldwide, likely leading to the collapse of stable governments.

Tipping points can no longer be viewed as future abstractions.  We are already passing them, cementing disastrous events in our future.  How many we pass, and by what degree, is up to us.


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Antarctic & Arctic News 1/26/09

A study was published in last Thursday’s issue of Nature and was covered in this MSNBC article.  It examined temperature trends across Antartica.  The continent as a whole has seen its average annual temperature rise 1F since 1957.  If Western Antarctica is contrasted with Eastern Antarctica, a very dramatic warming comes through: West Antarctica is 20F warmer and has warmed at twice the rate that East Antarctica has.  Previously, significant warming was noted for just the Antarctic Peninsula.  West Antarctica covers much more land surface than just the Peninsula.

The ozone hole is one cause for East Antarctica’s slower warming.  The hole influences the polar vortex, which distributes warm and cool air around the Antarctic Circle.  Cooler air has been maintained over East Antarctica since the 1970s than would have been the case without it.  Efforts in the late-20th century to stop destroying the ozone layer will continue to bear fruit throughout the remainder of the 21st century.  As the hole closes, the polar vortex will shift with it.  East Antarctica should begin experiencing more warming as the century goes on.

Very large ice sheets have broken off from Antarctica in recent years.  The rate at which the sheets are moving toward the ocean has accelerated, as they have in Greenland.  The Wilkins Ice Sheet is hanging on by a very tenuous piece of ice and should be the next sheet to calve.  These events are likely to increase in magnitude and frequency in the near-term.  Ice in West Antarctica rests below sea level.  If its melt increases, which wouldn’t take much more warming than has already occurred and is well within climate model projections, it will find its way to the oceans, rising sea levels.  It won’t take much sea level rise to significantly alter how coastal residents live.  A rise of only a few inches from current levels will impact millions of people worldwide.

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The Arctic is experiencing its third instance of very little to no ice growth since its minimum extent back in September:

In each instance prior to this, areal extent grew at climatologically normal rates.  Similar signals can be seen in the 2006-2007 data.  The progression of weather systems across the arctic is of course responsible for the temporary lack of growth.  I would say that it is unlikely that areal extent will match the climatological average this winter.  Conditions and this time series indicates to me that this winter is closer to the 2006-2007 winter than the climatological winter.  Maximum extent will be reached in approximately seven weeks’ time.  Then, the 2009 melt season is on.  What will things look like come September?

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