The collapse of the West Antarctic ice sheet will lead to a rise in sea level by three meters.
How much sea level will rise as a result of global warming? There is no clear answer to this question. The IPCC estimate is most often cited, but it is inaccurate, because the experts settled on the most conservative indicators - precisely because of the huge number of unknowns.
One of the many X's is Antarctica, the state of which is incredibly difficult to predict. A recent survey of research in the journal Nature Geoscience nicely summarizes the state of our knowledge of the West Antarctic ice sheet.
Antarctica is divided into two parts by the Transantarctic Mountains. For several reasons, the ice sheet west of the mountains is generally considered separate from the east. Although East Antarctica is larger, most studies focus on the western part, as it melts more.
The West Antarctic Ice Sheet is unstable due to the fact that the continent below it forms a large basin, the bottom of which is well below sea level. If the ice sheet melts enough to expose the outer ring of the basin, then the entire shield is likely to turn into an iceberg. But floating ice, as you know, is especially short-lived.
Something similar has happened in the past, but the dating of these events is very vague. Without knowing the timing, one cannot say how long it took to melt. It seems like it took several centuries. So that's enough for our age? Maybe yes, maybe no: they say that the current global warming is the fastest in recent geological time.
Satellite data show that the West Antarctic ice sheet is losing 100 to 200 Gt per year, which should raise sea level by 0.28–0.56 mm. This is comparable to the rate of melting in Greenland. However, climate models do not take Antarctica into account because they cannot adequately model the small-scale processes that affect mass loss. This is one of the reasons the 2007 IPCC report does not mention the upper bounds for sea level projections.
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The most severe losses in mass of the West Antarctic ice sheet occur where ice meets the Southern Ocean, either due to the formation of icebergs or due to the melting of ice shelves. The knowledge of physics is very important for researchers here, as floating ice shelves act as a support that slows down the movement of the glacier towards the sea.
Climate change is affecting melting indirectly through circumpolar deep waters. This water is warm enough to heat the bottom of the ice shelves, and has warmed an additional 0.2 ˚C since pre-industrial times. In addition, the changed wind rose drives it to the ice of the Amundsen Sea. With further warming, the picture may change, but so far this is the main reason for the melting.
Atmospheric warming is particularly affecting the Antarctic Peninsula, where pools of melt water form on the surface of the ice, leading to faults. The water in the cracks exerts such pressure that the crack can stretch for a kilometer.
The researchers conclude that we are unlikely to see the collapse of the West Antarctic ice sheet in this century, but the uncertainty of events does not allow us to calm down. Recall that the collapse will lead to a sea level rise of three meters.