....... and in the Southern hemisphere
Header source: http://www.antarctica.gov.au/news/2018/ocean-waves-following-sea-ice-loss-trigger-antarctic-ice-shelf-collapse.
After months of expectation, a one trillion tonne piece of the Larsen C ice shelf, the size of Bali, broke off Antarctica sometime between 10 and 12 July 2017. This follows the collapse of Larsen A in 1995 and Larsen B in 2002 and accounts for about 10% of the ice shelf’s total area. If the glacier that feeds the ice shelf melts, sea level rise will accelerate[1]. While the climate change signal is much clearer in the northern latitudes - where longer-term records show a relatively steady retreat of Arctic sea ice - evidence of global warming's impact around Antarctica is also showing up in the observations[2]. Larsen B’s demise was precipitated following a number of particular warm Antarctic summers[3].
After months of expectation, a one trillion tonne piece of the Larsen C ice shelf, the size of Bali, broke off Antarctica sometime between 10 and 12 July 2017. This follows the collapse of Larsen A in 1995 and Larsen B in 2002 and accounts for about 10% of the ice shelf’s total area. If the glacier that feeds the ice shelf melts, sea level rise will accelerate[1]. While the climate change signal is much clearer in the northern latitudes - where longer-term records show a relatively steady retreat of Arctic sea ice - evidence of global warming's impact around Antarctica is also showing up in the observations[2]. Larsen B’s demise was precipitated following a number of particular warm Antarctic summers[3].
Ice shelves like this have the potential to unleash a flood of ice from the continent that can significantly contribute to rising sea levels. Somewhat paradoxically, Antarctica’s melting ice sheets have rendered parts of the US East Coast more prone to flooding [4]. This is the subject of elaboration below.
Meanwhile, there are also concerns about the vast Pine Island and Thwaites Glacier Basin. Along with Pine Island Glacier, Thwaites Glacier has been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat. This hypothesis is based on both theoretical studies of the stability of marine ice sheets and recent observations of large changes on both of these glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces lowered, and the grounding lines retreated.[5]
Thwaites is starting to thin; and ice flows into the sea as the leading edge recedes inland. If the front edge of Thwaites retreated from the Coast back into the broad Bentley Subglacial Trench behind, it could make an ice face thousands of feet high, extending from far above the trench to deep down into it. Such a cliff could break fast, making incredibly tall icebergs that would roll over and float away through the trench outlet to the ocean, raising sea level by something like 11 feet if it were to retreat as far as the Transantarctic Mountains behind the Bentley. [6]
Meanwhile, a study published in late 2019 in the journal Nature Communications, revealed that sea levels rose as much as three metres each century about 130,000 years ago during the last interglacial period as Antarctic ice sheets melted leading to speculation that the IPCC consensus that sea levels will rise only about 2100 is too conservative, bearing in mind that the “climate forcing” from greenhouse gasses is much stronger today. If the Greenland and Antarctic ice sheets melted in their entireties, the rise would be in the order of 60 metres.
[1] http://www.pbs.org/newshour/rundown/antarcticas-larsen-c-ice-shelf-finally-breaks-releases-giant-iceberg/
[2] http://www.smh.com.au/environment/climate-change/attacked-from-two-sides-antarctic-sea-ice-hits-another-record-low-20170926-gyouuc.html
[3] Chelsea Harvey, “New crack emerges in major Antarctic ice shelf”, SMH, 5 May 2017, 7 (from the Washington Post).
[4] April Reese, “Swell or High water”, Scientific American, June 2017, 13.
[5] https://en.m.wikipedia.org/wiki/Thwaites_Glacier
[6] Richard B Alley, Professor of Geosciences at Pennsylvania State University, "Is Antarctica collapsing - Rapid glacier retreat could put coastlines under water sooner than inspected", Scientific American, February 2019, 36-41.
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