hi all,
I consulted with a few sea-ice wizards on the exchanges here related to Arctic trends, and Jennifer Francis at Rutgers weighed in with the following thoughts. Note the importance of the boundary layer changes as well. There are many important factors besides albedo and ocean solar absorption. Winter cloudiness etc important factor. But also note the importance of not over-interpreting short-term wiggles as trends. Much more on Dot Earth and in my earlier coverage of the sea-ice question. This post (shortcut) is a good starting point: http://tinyurl.com/dotIceTrends Here's jennifer's comment (I sent her that sea-ice graph that was making the rounds here)> Hi Andy -- The first figure you attached with the extrapolation from the 2007 summer ice loss is very unrealistic, in my opinion. Both the observed record and model simulations of ice extent exhibit a great deal of interannual variability, and most sea ice researchers would expect this behavior to continue superimposed on a continuing downward trend. Some years the decline will be dramatic, as it was in 2007, and some years there will likely be a recovery, as random atmospheric patterns act on the ice cover. What's different now as opposed to 2 decades ago is that the ice is now so thin that any unusual forcing -- be it a persistent wind pattern, cloud cover, heat transfer from lower latitudes -- will have a much bigger effect on the ice, as thin ice is more easily moved by wind and/or melted by increased heating. The small ice cover of recent years allows more solar energy to be absorbed by the open surface during summer, but exactly how that extra heat affects the system over the following months is still being worked out. Some recent research suggests that during falls after low-ice summers the lower atmosphere warms, the atmospheric boundary layer gets deeper, and low clouds increase, all of which tend to retard regrowth of sea ice in the fall and early winter. It also appears there's a large-scale influence on winter weather patterns over much of the northern hemisphere. The reason I'm telling you all this is that it appears there is no obvious mechanism for the ice to rebound significantly unless there is a multi-year period of colder-than-normal temperatures, but this is not likely as greenhouse gases continue to increase at rates even faster than the most pessimistic IPCC scenario. Regarding water temperatures, the main effect is through the added absorption of solar energy in summer, which accelerates the melt during late summer. Warmer winter temperatures in the Atlantic sector also appear to be responsible for most of the retreat of the ice edge during winter in that region, but not on the Pacific side. Maybe this is more info that you needed and much of it you already know, but it's not a simple explanation. Regarding the shipping text you sent, it looks like a bunch of hooey to me. 51 ships in the area will not have a perceptible effect on the clouds. The "good" low clouds they're talking about are already almost 100% emissive of infrared energy, and adding ship smoke to them is not going to matter. Hope this helps -- Happy New Year!! Jennifer ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Jennifer Francis, Ph.D. Institute of Marine and Coastal Sciences, Rutgers University Co-Director of the Rutgers Climate and Environmental Change Initiative 74 Magruder Rd, Highlands NJ 07732 USA -- Tel: (732) 708-1217, Fax: (732) 872-1586 fran...@imcs.rutgers.edu | http://marine.rutgers.edu/~francis/ At 9:14 AM -0700 12/29/08, wig...@ucar.edu wrote: >Re Arctic ice, the issue is not just albedo, but also thermai >inertia. The effective heat capacity of the exposed ocean is >hugely greater than the ice. > >Tom. > >++++++++++++++ > > -- Andrew C. Revkin The New York Times / Science 620 Eighth Ave., NY, NY 10018 Tel: 212-556-7326 Mob: 914-441-5556 Fax: 509-357-0965 www.nytimes.com/revkin --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
