There's an effect which I've not seen discussed here, but without doubt it's important. Ocean NOT covered by sea ice will radiate heat into space far more effectively than will the white ice it replaces. Ocean ice loss is potentially less significant than has been assumed. In fact, if the water uncovered is relatively warm, it could result in a greater loss of heat into space than would otherwise be the case.
Can the clever people (or the people with clever computers) estimate the significance of this effect? A 2008/12/29 Mike MacCracken <mmacc...@comcast.net>: > I would respond with two hopefully clarifying comments: > > 1. While there is a lot of focus on when the ice will be gone in summer, > this will have little effect on the weather as the surface temperature and > water availability are similar for no ice and melting ice. Indeed, more > solar is absorbed, but that does not significantly raise ocean temperatures. > What really matters is what happens in the fall into winter, because as long > as there is no ice or thin ice, there will be a lot of heat transport to the > atmosphere and so the near surface air cannot cool to –40 C and so create > cold, dense air masses that spread out from the Arctic and influence weather > around the midlatitudes. With all the extra heat going up into the > atmosphere (the solar heat absorbed during the time with lower albedo), the > atmospheric circulation will be altered—causing, as Jennifer notes, the > "large-scale influence on winter weather patterns over much of the northern > hemisphere." So, while the retreat of summer sea ice is an easy metric, what > really affects the weather is the delayed formation of thick ice that can > insulate the atmosphere from the heat contained in the ocean. > > 2. On the characteristics of low clouds, I thought the intent was to raise > the albedo when the Sun was out, not to raise the IR emissivity. During the > polar summer one wants the clouds with a high albedo (once the surface > starts to melt and its albedo comes down to below that of low clouds). Then, > during the polar night, one would want to decrease the cloud emissivity so > the surface can more rapidly radiate to space (the clouds tend to retard the > cooling process that allows ice to form, as Jennifer notes). > > Mike MacCracken > > > On 12/29/08 11:26 AM, "Andy Revkin" <anr...@nytimes.com> wrote: > > 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. > ++++++++++++++ > > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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