View source for Conclusions on the ice sheet in the instrumental period

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The Antarctic ice sheet is not behaving in a uniform manner &ndash; this is not surprising considering its enormous size, but the complexity and disparity of responses between different areas that has become observable in recent years might have been considered unlikely even a decade ago. The geographic extent of the ice sheet places different parts in markedly different positions within the global climate system and subjects them to different environmental drivers.

The most isolated portion is the East Antarctic ice sheet, primarily an extremely cold, high elevation plateau of ice, difficult for moisture-laden storms to reach. Recent atmosphere warming, pervasive throughout the rest of the planet, has not yet arrived, but slight increases in ice thickness are underway, likely an ongoing response on a centennial or millennial time scale to much older changes in climate.

Around the edges of the Antarctic ice sheet, the current state of the ocean is influencing the Amundsen Sea sector of West Antarctica and is likely also responsible for similarly behaving, but smaller, regions of East Antarctica. Here, the ocean appears to be the primary driving force, thinning the narrow fringing ice shelves, leading to rapid thinning and acceleration of the grounded ice. What happens at depth in the ocean matters to the ice sheet, and is itself strongly determined by the overlying atmospheric circulation, highlighting the complex climate interactions in this region. Other sectors of the West Antarctic ice sheet also contain fast moving ice streams, but aside from the now-stagnant Kamb Ice Stream and the decelerating Whillans Ice Stream, their current behaviour is far less extreme.

Ice on the Antarctic Peninsula is behaving quite differently from the rest of the continental ice sheet, in that it is engaged in an active interaction with a currently warming climate. Its north-south topography is the only barrier to the east-west atmospheric and oceanic circulation at these latitudes. Here, high rates of snow accumulation and melting drive a more vigorous glaciological regime. Recent observations have captured the sudden, and very likely recently induced, succession of ice shelf disintegrations followed by the dramatic acceleration of the glaciers that fed them. Perhaps more than any other single phenomenon, these events heighten concern about the near-future impact on global sea level of change in much larger ice reservoirs.

The attribution of ice loss on the Antarctica Peninsula to human-driven warming is now strong, and although not yet proved conclusively, there is a strong hypothesis that a similar case can be made for West Antarctic thinning. The thickening on parts of East Antarctica is an expected consequence of climate change, but it is not yet possible to make a satisfactory attribution of the changes there to any specifically observed climate change.
[[Category:The instrumental period]]
[[Category:The Antarctic ice sheet]]