212 Journal of Human Rights and the Environment, Vol. 8 No. 2 Totten is also specifically a marine-based ice sheet, and the Tasmania-based research team found, as we have seen, hard physical evidence that the mechanism of basal melt by ocean heat flux is at work under the ice shelf that buttresses the ice sheet. Several years ago I introduced the concept of a ‘threshold likelihood’ of catastrophic human losses, which obtains when ‘(a) the mechanism by which the losses would occur is well understood, and (b) the conditions for the functioning of the mechanism are accumulating’.24 Both WAIS and the Totten Glacier have unfortunately turned out to be paradigm cases of threshold likelihood. I argued then that when such massive losses had threshold likelihood, we should take action to prevent them in spite of not being able to calculate a probability of their occurrence, provided only that the costs were not excessive. Knowledge of a calculable probability is unnecessary when threshold likelihood has been established for a possible human catastrophe that can be prevented at non-excessive cost. Lauren Hartzell-Nichols has subsequently incorporated threshold likelihood into her carefully constructed Catastrophic Precautionary Principle.25 A rise in sea-level of an additional 3 metres from the melting of the Totten Glacier, especially in combination with the 3 metres from the melting of the WAIS, would undoubtedly constitute a human catastrophe for every nation with a sea-coast. To choose not to mitigate our emissions now at the maximum affordable rate, but instead to rely on the possibility (with no calculable probability!) of somehow fully adequate future negative emissions would be to choose to ignore the threshold likelihood that between now and when BECCS, or whatever turned out to be the NET of choice, took a substantial bite out of the emissions ‘over-shoot’ at the global scale our lack of ambition would have opened the door to – allowed the planet to pass the threshold for – the beginning of the irreversible melting of the Totten Glacier. Gambling that the tipping point for the irreversible melting of Totten would not be passed would be an outrageously reckless act – an utterly unjustified risk transfer. To save ourselves some trouble and expense, and whatever they might risk for us, we would risk catastrophe for future generations from sea-level rise. 5.2 Do the oceans ever forget? Some other irreversible – or if you like, very long-term – effects last ‘only’ for centuries, not millennia, and are not usually included in the customary lists of tipping points. But they affect foreseeable human interests just as decisively. For example, researchers – including Susan Solomon of MIT, a former chair of the IPCC working group on the basic science of the climate (Working Group I) – have recently drawn a striking conclusion about the famously ‘short atmospheric life-time’ of the greenhouse gas methane, a conclusion which Solomon has summarized informally as DeConto and Pollard is B Dennis and C Mooney, ‘Scientists Nearly Double Sea Level Rise Projections for 2100, because of Antarctica’ (2016) Washington Post, 30 March, <https://www. washingtonpost.com/news/energy-environment/wp/2016/03/30/antarctic-loss-could-doubleexpected-sea-level-rise-by-2100-scientists-say/?wpisrc=al_alert-hse> accessed 30 April 2017. 24. H Shue, Climate Justice: Vulnerability and Protection (Oxford University Press, Oxford 2014), 265. 25. L Hartzell-Nichols, A Climate of Risk: Precautionary Principles, Catastrophes, and Climate Change (Routledge, New York and London 2017). © 2017 The Author Journal compilation © 2017 Edward Elgar Publishing Ltd