SEA LEVEL RISE

How much will/does Antartica contribute to sea level rise (and does it)?

You can find the article here: https://www.nature.com/articles/nature17145

This article was published in Nature, by DeConto and Pollard, in 2016.
Antarctic ice sheets were the primary contributor the last times sea levels have risen significantly (which was during the Last Interglacial –130000-115000 years ago—and the Pliocene epoch). The authors use a model which links ice sheet dynamics and climate dynamics, by taking into account the warming of the atmosphere to consider the collapse of ice cliffs. First they look how to simulate the ancient sea level rising events (Pliocene and Last Intergl.), which were driven by MISI and/or MICI and ocean warming. Then they apply the model to scenarios where the warming is caused by greenhouse gas emissions (they consider three different scenarios of future greenhouse emissions, see below). The result is that Antarctica can contribute to more than 1m of sea level rise by 2100 and more than 15m in the next 500years. Though the warming of the ocean is important for determining the melting of ice sheets, the authors consider long-term sea level rise to be due to atmospheric warming caused by greenhouse gases. Finally, because of the processes involved (MICI and MISI), in these scenarios, the grounding of the ice sheets would melt. Hence, grounding ice would be unable to reform and recover even after the reduction of greenhouse gases.

How? They looked at sea level estimates during the Pliocene and Last Interglacial and then applied those estimates to see how ice shelves would react if we take into account the greenhouse gas emissions of the future (in particular they use three Representative Carbon Pathway scenarios, RCP2.6, 4.5 and 8.5). RCP2.6 produces almost no net change until 2100, while RCP4.5 causes a sea level rise of up to 32cm by 2100; 8.5 causes first a gain in ice mass due to rains and then a rapid melt causing up to 77cm sea level rise by 2100. The warming ocean could erode the grounding of ice shelves very quickly (about 10 m per year), this is calles MISI (Marine Ice Sheet Instability) leading to increased water discharge. The model takes both MICI and MISI into account.

What’s MISI and MICI: “Marine ice sheet instability (MISI) occurs when the grounding line of marinate-terminating glaciers is forced to retreat over a retrograde bed, which causes increasing ice discharge across the grounding line. Observations and modelling studies indicate that the process of MISI has already begun at Thwaites Glacier. The future retreat of Thwaites Glacier may also be exacerbated by marine ice cliff instability (MICI), a process in which an ice front that is rapidly retreating into a deepening basin becomes increasingly unstable. This could lead to runaway ice cliff failure and further ice sheet disintegration.” From: http://standrewsglaciology.org/research/dominos

 

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