On Tue, 19 Jun 2007, Michael Tobis wrote: > If I understand correctly, if the Thwaite Glacier retreats a couple of > km behing a sub-sea-level ridge it is currently resting upon, there's > a scenario which can't be eliminated whereby about a quarter of the > WAIS turns into a huge relatively fast flowing glacier leading to as > much as 2 meters sea level rise on a time scale on the order of a > century. It would be like popping a cork on a bottle; the ice sheet > would just spill out the opening. > > This is summarized in Hansen's "rising sea level helps unhinge the ice > from pinning points". > > I'm not sure this is regarded as likely, but it at least it's not very > unlikely.
Is it "can't be eliminated" or " not very unlikely" or what? Really quite improbable would be my view. I don't think ice sheet behave like champagne. But since H isn't saying this, we're getting a bit off track. > The quaternary record does indeed show abrupt warmings and sea level > rises, and recent observations have revealed new mechanisms of abrupt > ice failure. > > Why should we be immune to abrupt failures of ice sheets. They have > happened in the past. > > In what way is the analogy to the paleo record unsupportable? The idea that it supports his predictions of less than century-timescale rapid sea level rise. > I think Hansen carefully avoided quantitative predictions. Informally > speaking, over a meter of sea level rise in excess of thermal > expansion, in this century, is not at all off the table from what I am > hearing from people whose business it is to think about this problem. > > I am sure you hear from others, but I don't know why they or you feel > confident in discounting this. As you say, H is a bit vague on the quant side. I'm disliking his language mostly: "Recent greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures." or, "Our concern that BAU GHG scenarios would cause large sea-level rise this century (Hansen 2005) differs from estimates of IPCC (2001, 2007), which foresees little or no contribution to twenty-first century sea-level rise from Greenland and Antarctica. However, the IPCC analyses and projections do not well account for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, nor are they consistent with the palaeoclimate evidence we have presented for the absence of discernable lag between ice sheet forcing and sea-level rise." -W. > mt > > > William M Connolley | [EMAIL PROTECTED] | http://www.antarctica.ac.uk/met/wmc/ Climate Modeller, British Antarctic Survey | 07985 935400 -- This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. Any material supplied to NERC may be stored in an electronic records management system. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
