Unusually warm water beneath its grounding zone (grounding line) is accelerating the melting of a key Antarctic glacier (74,000 sq. mi). New research on the Thwaites Glacier (lately dubbed the Doomsday Glacier by no less than FOX News) on the West Antarctica Ice Sheet shows the water underneath the floating ice shelf to be about closer to 36F. The glacier is melting from below.
The Thwaites mass is an Ice Shelf, a hybrid formation that rests on bedrock on one end while floating on the other. The grounding line of these ice shelves – where the glacier meets land – anchors the ice, and also serves to hold back the much larger mass of land ice behind it. The existence of warm waters beneath the grounding line is more bad news for the stability of the Antarctic continent and the growing threat of rising sea levels.
Mar 1: Antarctica is about to lose another major chunk off of the Brunt Ice Shelf in West Antarctica. This New York City-sized sheet will be the largest ever observed. If you want to know why ice shelves are important, find more here.
Feb 10: Petermann Glacier, Greenland’s longest, has formed new cracks and appears to be accelerating it’s collapse into the ocean. A Manhattan-sized chunk broke away in 2012. The flow of this has increased by about 10% since then. This is freshwater that increases sea level, but also changes the salinity of the ocean, which could be worse long term.
A massive cavity – described as nearly the size of Manhattan – has been found in Thwaites Glacier in West Antarctica. This means that this huge glacier has been falling apart from inside, more or less out of view of satellites up to this point. The cavity would have held 14 billion tons of ice. If the water frozen in the Thwaites melted into the ocean, it would contribute two additional feet of sea rise.
This is only the latest bad news from way down under, where the Antarctic ice sheet is melting about six times faster than 40 years ago. It is collapsing at a rate of 250 billion tons annually. That is flowing into the ocean.
I have been surprised that most people don’t differentiate among the types of polar ice and what is happening with each. The rapid disappearance of sea ice is driving one of the most powerful climate feedbacks. The rapid melting of land ice contributes to sea level rise and changes the salinity of the ocean. The ice shelves are what are holding back land glaciers.
A straightforward summary of polar ice collapse and what it means for the rest of the planet is Here
Antarctic land ice melt is 6X faster than 1980's rate: Jan 13 - Two alarming new research reports (University of California) tell us that the rate of Antarctic land-ice melt has increased 280% over the past four decade. The current rate - which is accelerating - is enough to add one millimeter a year in sea level rise. New estimates indicate an end-of-century rise over near 200 ft. Ice has increased from 40 gigatons / year from 1979-90 to 252 gigatons per year from 2009-17. Six times faster.
Jan 19 - Antarctic sea ice sets a new record for all time low extent.
There are three types of ice that play a role in global warming. It is important to distinguish among them when discussing the affects of melting ice and the resulting feedback loops have on climate change patterns.
The key characteristic of land ice is that it has not been in the ocean. When it melts, it contributes to the total volume of water in the oceans.
Slowdown of global currents (including the critical Gulf Stream) is driven by freshwater pouring into the ocean from melting glaciers on Greenland and Antarctica. Differences in salinity between depth layers drive the global overturning current.
This hybrid ice class is critical to the rate of melt for onshore ice sheets. To a large degree, ice shelves are what is holding back the flow of glaciers into the ocean, especially in Greenland and Antarctica. As the ice shelves of Antarctica break up in dramatic fashion, the land ice behind them begins to flow faster. That is what is happening now.
Ice that floats in the water and it’s affect on climate is tricky to measure, but the general trends are crystal clear. The extent of ice pack decline has been verifiable for decades, with the total area covered reduced by about 70% since 1978. Equally important, but harder to measure, is ice thickness, which can now be measured by satellite. Compared to the lowest extent year of 2012, this year’s extent is slightly greater, but the all important class of “multi-year” ice is far less. The thickness of the remaining ice is also starkly less.
“The Arctic is going through the most unprecedented transition in human history,” Jeremy Mathis, director of NOAA’s Arctic research program, said at a press conference. “This year’s observations confirm that the Arctic shows no signs of returning to the reliably frozen state it was in just a decade ago.”
The rapid melting of sea ice is one of two major polar feedback loops that are accelerating global warming beyond the point of no return. Read more about feedback loops.