210 Journal of Human Rights and the Environment, Vol. 8 No. 2 5.1 Does the melting ever stop? Some of the irreversible effects of allowing carbon emissions to continue for too long result from what are usually referred to as ‘tipping points’: points of no return. ‘No return’ is obviously relative to some time-scale. Some conditions may revert to what humans now consider to be normal after millennia, or after millions of years. We know from the geological record that this planet passes through deep cycles over vast periods of time: ice forms, sea-levels decline, and dry land expands; ice melts, sea-levels rise, and dry land shrinks.18 Here I will refer to a change that persists for many centuries as permanent and will say that passing the threshold for such a change is passing a point of no return. This focuses the argument on changes that affect human interests that we can conceivably be concerned about. For other purposes one could adopt different criteria for ‘irreversibility’ and understand ‘no return’ with even longer time-frames. The lists of potential tipping points for climate that may lie in the near future usually include disruption of the Atlantic meridional overturning circulation, the melting of Arctic permafrost releasing both carbon dioxide and methane in positive feedback of earlier warming, and the melting of the massive ice sheets of Greenland, West Antarctica, and East Antarctica that currently withhold vast amounts of water out of the oceans and for now free up many square miles of coastal land all over the planet that would otherwise be submerged under oceans. We can glance briefly at the melting of ice sheets that would drive rises in sea-level. In 2014 the scientific world was electrified by the dramatic news that two independent studies by teams of eminent cryospheric scientists had concluded that the West Antarctic Ice Sheet (WAIS) is probably already melting irreversibly.19 In other words, the tipping point for West Antarctica has probably already been passed, which means that over the coming centuries the sea-level will rise by 3 metres. This much sea-level rise will inundate scores of coastal cities. Subsequent examination of the two initial studies by other leading specialists uninvolved in them has confirmed their conclusions.20 One of the most dramatic elements of these findings is the specification of the working of a mechanism by which the ice sheets are undercut from below – literally – by warming ocean water in addition to the effects of the warming atmosphere above. Ice sheets rest on land; this is what distinguishes them from ice shelves, which by definition float on the ocean, often immediately in front of ice sheets, which they ‘buttress’ – hold back from sliding into the sea. But although ice sheets by definition rest on land, in some cases that land is itself far below the surface of the ocean so the 18. D Archer, The Long Thaw: How Humans are Changing the Next 100,000 Years of Earth’s Climate (Princeton University Press, Princeton 2009). 19. I Joughin, B Smith, and B Medley, ‘Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica’ (2014) 344 Science 735–8, doi:10.1126/ science.1249055; E Rignot, J Mouginot, M Morlighem, H Seroussi, and B Scheuchl, ‘Widespread, Rapid Grounding Line Retreat of Pine Island, Thwaites, Smith, and Kohler Glaciers, West Antarctica, from 1992 to 2011’ (2014) 41 Geophys. Res. Lett., 3502–9, doi:10.1002/ 2014GL060140. A non-technical account of the significance is found in T Sumner, ‘No Stopping the Collapse of West Antarctic Ice Sheet’ (2014) 344 Science, 683, doi:10.1126/ science.344.6185.683. 20. R Alley et al., ‘Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More’ (2015) 43 Annual Review of Earth and Planetary Sciences 207–31, doi:10.1146/annurev-earth060614-105344. © 2017 The Author Journal compilation © 2017 Edward Elgar Publishing Ltd