The ‘Ice Pump’ is eating into the West Antarctic Ice Sheet. This could melt enough ice to raise sea levels by 6.4 meters. While such melting will take a long time it adds to other sources of sea level rise. Scientists advising the United Nations report ‘deep uncertainty’ and give a range of possible sea level rise by 2300 of just under 1 meter to 5.4 meters. This is a worry given land near Hong Kong’s Deep Bay and large areas north of Macau are less than 2 metres above sea level.
So how does the Ice Pump work?
The Ice Pump is driven by the changes in water density which happen as its salinity (how salty it is) and temperature vary.
The story starts between Greenland and Iceland where warm, salty surface water brought from the Caribbean by the Gulf Stream cools to about 4°C (when water is densest) and sinks to near the bottom of the ocean where it joins the Atlantic Conveyor Current taking it south to join the deep current circling Antarctica. Some of the warm water is then drawn to Antarctica’s ice sheets by the ‘Ice Pump’ in a process which starts slowly and builds up speed. First some deep warm touches the glacier melting a little. This melt water is less salty and so less dense causing it to flow up along the bottom of the glacier dragging more of the denser warm water under the glacier and causing more melting. This is the ‘Ice Pump’:
The Ice Pump is strongest where the sea bed under the glacier slopes downwards away from the sea. This is the case for over 400 kilometres of the Thwaite’s glacier:
Comparing West Antarctica with China and South East Asia on the same scale gives an idea of the size of the problem:
For more information see the BBC’s January 2020 story about the Thwaites glacier see: www.bbc.com/news/science-environment-51097309
 Source: IPCC SROCC SPM page 6 Sept 2019. The uncertainty is due to both how fast the West Antarctic Ice Sheet might melt and the extent to which humanity will curb its greenhouse gas emissions.