There are (roughly) two mechanisms via which ice sheets decline: in situ melting leading to runoff, and direct transport of ice into the oceans via ice streams. We have a moderately good theoretical understanding of melting and a quite poor understanding of mass transport. If I understand correctly, mass loss from greenland in the present day is mostly the first type. The ice streams originating from Greenland have fairly limited cross-sections compared to the volume of the ice sheet as a whole, and so are only a small portion of the total contribution. Since such flows tend to be geographically constrained, the cross-sections may remain fairly limited even as the Earth warms. The big question is how fast can the ice streams accelerate.
However, as noted in the current IPCC discussion, even if the streams accelerate substantially, the limited width of the outflows originating from Greenland may still limit the impact. Even a very large increase in flow rate may only contribute some tens of centimeters of additional sea level rise, rather than meters, during this century. So, even though the knowledge of ice flows is quite limited, some geographical constraints suggest that the impact of ice flows from Greenland could remain moderate rather than severe. By contrast, ice discharge could play a major role in the evolution of the West Antarctic ice sheet, but the IPCC continues to predict that increased precipitation will keep the Antarctic stable during this century (i.e. no net mass loss). -Robert A. Rohde http://www.globalwarmingart.com/ On Jul 26, 9:52 am, "Michael Tobis" <[EMAIL PROTECTED]> wrote: > I think he has an interesting argument: > > 1) The ice sheets are so far out of equilibrium that an exponential > increase in their net decay is a reasonable approximation. > > 2) The doubling time for the rate is about a decade. > > I suspect point 1 fails to hold once we get into significant fractions > of a meter per decade, and I have no idea how he calibrated point 2, > but I think both points are quite plausible and worth discussing. > > I agree that the "almost inconceivable" is disturbingly excessive. > > mt --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
