Well, here is a can of worms. William does a nice job of explaining the residual here:
http://mustelid.blogspot.com/2005/07/harry-potter-and-polar-amplification.html but I don't think it tells the whole story. William dismisses and Dr Bitz does not mention the idea that CO2 warming is more effective where the column H2O is thin. The mechanism is real enough. How effective it is depends on how much H2O absorption bands and CO2 long-wave (a.k.a. infrared) absorption bands overlap. I'm no expert on this, but I usually refer to figure 6.2 in Peixoto & Oort's Physics of Climate for things of the sort. The overlap appears sufficiently substantial to me that it might matter. I don't have a reference handy. Here's yet another mechanism, as described by Igor Esau of Norway: http://www.iarc.uaf.edu/calendar/main.php?view=event&eventid=1175032736000 One more possible mechanism contributing to the polar amplification is a convective adjustment. The convective adjustment is a dynamical response of the lower atmosphere, namely, the turbulent planetary boundary layer (PBL), on development of instabilities due to advection and radiation processes. In high latitudes, the turbulent exchange is suppressed so that the advection and radiation heat fluxes are comparable with the turbulent fluxes for the largest part of the year. In this circumstances, details of the vertical turbulent exchange determine the near-surface heat balance and therefore temperature. I show that static stability of the PBLs may be increase climate sensitivity. I am pretty sure this isn't news and I've had discussions about this mechanism or something like it in the past. That makes no fewer than four terms acting in the same direction. Paleoclimate evidence shows that in ice free periods in the deep past the polar area gets a much bigger warming shift relative to today than does the tropical area. Even with all these mechanisms it is regarded as something of a puzzle how large cold-blooded gator-like things lived on Alaska's north slope. (This was 150 million years ago, too recent for continental drift to explain.) http://www.sciencemag.org/cgi/content/full/282/5397/2199?ck=nck I came across a thesis (PhD or Masters, unclear) which addresses the matter and mentions no less than five mechanisms, all courtesy of the ACIA (Arctic Climate Impact Assessment) report. See section 5.2 . http://www.diva-portal.org/diva/getDocument?urn_nbn_se_su_diva-6585-2__fulltext.pdf I think the one we are missing is increased efficiency of heat transfer from ocean to atmosphere as sea ice retreats. Your google search term is "polar amplification". 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 -~----------~----~----~----~------~----~------~--~---
