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A man-made morality tale
...By contrast with the forecasts made by others, those essayed in the summary are quite circumspect. We can see this, briefly, in its treatment of temperatures, and at greater length in its treatment of ice and sea levels. The potential temperature rises projected in the summary are not dramatically different from those in the IPCC’s 2001 Third Assessment Report. The ‘best estimate’ made by the summary is that of a temperature rise of between 1.8º and 4.0º by 2100. It considers ‘unlikely’ changes of less than 1.1º or more than 6.4º. Already this confirms the mischievousness of Monbiot and Stern. They mention figures as high as 11.5º (13).

What about ice and the sea? Gore warns that if Greenland’s or the Antarctic’s ice melt, sea levels would rise by up to six metres. His maps show the inundation of Florida, San Francisco, Beijing, Calcutta and the Netherlands. The front page of the UK Independent goes further. Invoking the summary as ‘the final warning’, environmentalist writer Mark Lynas says that, with a temperature rise of 5.4º, ‘the entire planet will become ice-free, and sea levels will be 70 metres higher than today’ (14). How do Gore’s six and the Independent’s 70 metres compare with the summary? It considers a variety of scenarios in which no special policies are implemented to deal with greenhouse emissions. Its conclusion: by 2100, sea levels could rise by between 18 and 59 centimetres.

All this is an order of magnitude less pessimistic than Gore and the Independent. When the summary speculates about ‘virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about seven metres’, that is in the context of melting being sustained not to 2100, but for millennia (15). And the Antarctic? The summary does say that a net loss of ice mass could occur if ‘dynamical ice discharge’ dominates the ice sheet – in other words, if bits of ice break off rather than melt. But it precedes that observation with the point that current global model studies project that the Antarctic ice sheet ‘will remain too cold for widespread surface melting and is expected to gain in mass due to increased snowfall’ (16).

Alarmists such as Gore make much of the recent suggestion that the world’s ice may be melting much more rapidly than previously thought. But once again the summary is more sober. It says: ‘Models used to date do not include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future.’ (17)

As for the newer studies, the summary suggests that increased melting might raise sea levels by between 10 and 20 centimetres. Larger values, it adds, cannot be excluded; but ‘understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise’ (18). All the most worrying scenarios for rises in sea levels rely on the melting of Greenland or Antarctic ice. As noted above, the IPCC suggests that such processes will take millennia. Gore, Monbiot and Stern and others claim that we should take seriously much shorter timescales. While the IPCC uses uncertainties about melting as a reason for withholding judgment, Stern, an economist, speculates that ocean warming and the acceleration of ice flows could lead to a ‘runaway discharge’ of ice. ...