Pine Island Glacier collapse inevitable This image was taken by the MODIS instrument on NASA’s

Pine Island Glacier collapse inevitable This image was taken by the MODIS instrument on NASA’s Terra satellite on January 5th, 2014, and it shows an iceberg in Antarctica’s Pine Island Bay. The iceberg began as a crack in Pine Island Glacier last November and broke away as a piece the size of Singapore in early January. The Pine Island Glacier is a major feature of West Antarctica. Western Antarctica is covered by an ice sheet. When snow falls on top of that ice sheet, it pushes older ice out towards the coast through a series of “ice streams”. The Pine Island glacier is one of these ice streams; about 20% of West Antarctica’s ice flows through its channel and you can even see streaks at the bottom-right of this image marking its flow direction. The Pine Island glacier is also one of the least stable in Antarctica. Over the last 20 years it has shrunk rapidly, contributing several millimeters worth of sea level increase over that time. New research just published in the journal Nature Geoscience suggests this is just the beginning, and over the next few decades a large portion of this glacier is going to collapse. This type of ice stream typically starts on land and moves out to sea. It pushes ice out to sea, forming a shelf of ice floating offshore. Further up, there is a “grounding line” – the point at which the glacier goes from sitting on land to floating on the oceans. Above the grounding line the glacier is anchored to rocks at the base; below the grounding line the glacier is exposed to the waters of the ocean. Much of the melting of this glacier over the last 20 years is due to the ice shelf shrinking. When warmer waters come up beneath the ice shelf, they cause ice to melt and to break away as icebergs, and as the ice shelf shrinks the glacier begins flowing faster as the sea ice helps hold the rest of the glacier in place. But the Pine Island glacier is unique in an important way; its grounding line sits on an underwater ridge. The rocks that this glacier was hanging on to had another bay behind them where the waters got deeper. Water from the warming ocean couldn’t get into this bay because the glacier was grounded farther out to sea, but this setup created a precarious situation. What would happen if the glacier lost its grounding point on this underwater ridge? The glacier would lose all of its support. The next possible grounding point is tens of kilometers farther up. If the glacier lost contact with this underwater ridge, the glacier would become extremely unstable. New research just published in the journal Nature Geoscience says that is exactly what has happened. Based on radar surveys taken through the ice, the Pine Island Glacier has now lifted completely off this ridge. Warmer waters from the open ocean are now free to flow along the entire base of this glacier; it is no longer pinned in place and has crossed a point of no return. Using models for how ice flows over topography, the scientists modeled the behavior of this glacier without the pinning point and project that it is in an irreversible retreat. The glacier will melt at the base weakening it and over time ice will break off until it retreats tens of kilometers to its next grounding point. The current structure of this glacier is going to collapse. The Pine Island Glacier is already the largest contributor to sea level rise on the Antarctic Continent. Based on these models, the scientists project that over the next 20 years, it is likely that this glacier will contribute 3 to 5 times as much to sea level rise as it did during the last 20 years and possibly more. The unsupported part of this glacier is going to die. It will retreat back to the new grounding line, dumping large amounts of water into the ocean and causing flow from the continental ice sheet to accelerate. -JBB Original article:http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html Image credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Teamhttp://www.flickr.com/photos/gsfc/11949193796/ Read more:http://www.bbc.co.uk/news/science-environment-25729750http://www.independent.co.uk/environment/climate-change/pine-island-glacier-melting-past-the-point-of-no-return-9059347.htmlhttp://www.reportingclimatescience.com/news-stories/article/pine-island-glacier-committed-to-irreversible-decline.html -- source link

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