Climate dreaming 211 point at which the ice last rests on land – the ‘grounding line’ – is under water. So these are labelled marine-based ice sheets: they rest on land under water. This obviously means that the forward edge of the ice sheet at the grounding line is in contact with ocean water. If the ocean water is warm enough, it can melt the front of the bottom edge of the ice sheet. Scientists sometimes refer to this as ‘basal melt by ocean heat flux’. If, worse, the land at the grounding line slopes downward as it goes inland, any melting can proceed downhill. This is what makes the process seem to be irreversible. Nothing is known that would stop the water from going downhill, ‘lubricating’ the base of the ice sheet, and allowing its pre-existing slide toward the sea to speed up. The glacier that is the ‘keystone’ for the West Antarctic Ice Sheet is a marine ice sheet with its grounding line on inwardly sloping land with a downward incline. Now multiple lines of evidence have been found that this same mechanism may be beginning to work on the Totten Glacier, which is the keystone helping to hold back a huge portion of the East Antarctic Ice Sheet (EAIS). ‘The Totten Glacier drains more ice than any other glacier in the EAIS and contains a volume of marine-based ice above flotation equivalent to at least 3.5 metres of global sea-level rise, comparable to that of the WAIS’.21 An intrepid team of scientists led by researchers from the University of Tasmania sailed on the RSV Aurora Australis right up to the front edge of the ice shelf buttressing the Totten Glacier – the ‘Totten calving front’ – and directly measured deep warming water that is flowing in underneath ‘through a newly discovered deep channel’. They conclude that the same general mechanism at work in West Antarctica – basal melt by ocean heat flux – is also at work in the East: several lines of evidence support the conclusion that rapid basal melt of the TIS [Totten Ice Shelf] is driven by the flux of warm mCDW [modified Circumpolar Deep Water] into the cavity: the presence of warm water at the ice front, the existence of a deep trough providing access of this warm water to the cavity, direct measurements of mass and heat transport into the cavity, the signature of glacial meltwater in the outflow, and exchange rates inferred from the heat budget and satellite-derived basal melt rates.22 Now, no one is claiming that the melting of the Totten Glacier is also already irreversible. That it is not yet irreversible is the point here, after all – what happens may depend on what we do. What we do now is supremely important for the extent of ocean invasion of now-dry land. New marine sediment evidence regarding the last interglacial period from 129,000 to 116,000 years ago has led a leading cryospheric scientist not involved in this particular new research to conclude: ‘The big ice sheets are really sensitive to just a little bit of warming. That’s a really powerful message’.23 21. S Rintoul, A Silvano, B Pena-Molino, et al., ‘Ocean Heat Drives Rapid Basal Melt of the Totten Ice Shelf’ (2016) 2 Science Advances e1601610, 1. An account of the article for laypersons is: C Mooney, ‘Scientists Confirm that Warm Ocean Water is Melting the Biggest Glacier in East Antarctica’ (2016) Washington Post, 16 December <https://www.washingtonpost.com/ news/energy-environment/wp/2016/12/16/warm-ocean-water-is-slamming-into-and-meltingthe-biggest-glacier-in-east-antarctica/?utm_term=.e103e52049f9> accessed 30 April 2017. 22. Ibid at 4. 23. Robert DeConto, quoted in Hannah Devlin, ‘Sea Levels Could Rise by Six to Nine Metres Over Time, New Study Warns’ (2017) The Guardian, 19 January. The underlying study is J Hoffman, P Clark, A Parnell, and F He, ‘Regional and Global Sea-surface Temperatures during the Last Interglaciation’ (2017) 355 Science 276–9, doi:10.1126/science.aai8464. Also see R DeConto and D Pollard, ‘Contribution of Antarctica to Past and Future Sea-level Rise’ (2016) 531 Nature 591–7, doi:10.1038/nature17145. An accessible account of the significance of © 2017 The Author Journal compilation © 2017 Edward Elgar Publishing Ltd