"The main issue is: How fast will ice sheets respond to global warming? The IPCC calculates only a slight change in the ice sheets in 100 years; however, the IPCC calculations include only the gradual effects of changes in snowfall, evaporation and melting. In the real world, ice-sheet disintegration is driven by highly nonlinear processes and feedbacks. The peak rate of deglaciation following the last ice age was a sustained rate of melting of more than 14,000 cubic kilometers a year—about one meter of sea-level rise every 20 years, which was maintained for several centuries. This period of most rapid melt coincided, as well as can be measured, with the time of most rapid warming. Given the present unusual global warming rate on an already warm planet, we can anticipate that areas with summer melt and rain will expand over larger areas of Greenland and fringes of Antarctica. Rising sea level itself tends to lift marine ice shelves that buttress land ice, unhinging them from anchor points. As ice shelves break up, this accelerates movement of land ice to the ocean. Although building of glaciers is slow, once an ice sheet begins to collapse, its demise can be spectacularly rapid. . . . These considerations do not mean that we should expect large sea-level change in the next few years. Preconditioning of ice sheets for accelerated breakup may require a long time, perhaps many centuries."
It sounds as if Micheals is being disengenuous, but this statement by Hansen is disingenuous as well. This period of most rapid melt also occurred when glacial ice was located as far south as the Washington DC region and is not applicable to the present day scenario where glacial ice is found only in Greenland and Antarctica. And rapid desalination of the North Atlantic from this melting of mid-latitude glaciers would have accelerated the warming/melting of glacial ice. Also not applicable to present day scenarios - but Hansen implies that the present day warming trend will similarily affect near-polar region glaciers.