Hi Jim—I’ll certainly agree climate can be path dependent, so some locations in climate space that are like attractors. The classic suggestion, however, that the energy balance models gave that had a snow-covered Earth as an additional possibility I believe was flawed due, at least in part, to their failure to treat the diurnal cycle (there is, in my view, just no way that high albedo snow survived under the noonday tropical sunlight).
I’d also comment regarding climate sensitivity that the concept itself has problems—a good example being that orbital element cycles top of the atmosphere have virtually no change in annual, global integral, but the result is ice ages, so a very large climate change from a redistribution of incoming solar by season and latitude. IPCC and others account for this by counting the ice sheet albedo as an external forcing, but that is only plausible because (most—Berger et al. do) computer models can’t run long enough to simulate ice sheets as an internal feedback. Given both issues, I guess the admonition we’d both agree on is be careful and thoughtful. Mike On 2/27/12 9:09 AM, "Jim Fleming" <[email protected]> wrote: > Dear Mike, > > Fine, but those quotes are from papers by Lorenz on climate, not weather. > They are not essentially about the propagation of transient signals or random > events, or even "stability," but, as he says, indicate that the solutions to > any boundary constraints plus dynamic forcings lie along attractors. That is, > there are multiple solutions and we can't treat forcings as linear, at least > in the "climate of the models" he was exploring. > > Jim > > > > On Sun, Feb 26, 2012 at 8:50 PM, Mike MacCracken <[email protected]> wrote: >> Hi Jim--I think you need to be careful in applying the Lorenz butterfly >> effect to climate--the equations are for the weather and how it varies >> within a system that is bounded by external conditions. >> >> For climate, so the average of the weather when there are a particular set >> of external boundary conditions. Now, the climate can certainly have some >> path dependent phenomena--so hysteresis of various types (e.g., Greenland >> ice sheet, carbon cycle given the various ways it gets stored and released, >> etc.), but I just don't think that it is random in the sense that Lorenz was >> portraying the situation for the weather. >> >> Certainly there is some variability given a certain set of external boundary >> conditions and so it can seem that the climate sensitivity varies somewhat, >> and it is certainly possible that one can get to points where there may be a >> jump between different possibilities created by hysteresis (like we can >> reach a warmth were Greenland ice sheet melts away, and this might happen >> pretty rapidly), but I would not call this a random sort of event in the >> butterfly sense. >> >> As to the paleoclimatic jumps, it may well be that there are causal >> mechanisms for those--bursting of ice dams and outflow of freshwater, etc. >> Again, that does not really seem random to me, but a process that can have >> jumps--and it may be hard to predict precisely, but is it really a butterfly >> event, etc. It seems to me were the Earth system's climate, we'd have not >> had so many millions of years between major glacial periods, we'd not have >> had the stable Holocene, we'd not be finding the Milankovitch cycles, etc. >> >> Best, Mike MacCracken >> >> On 2/26/12 1:16 PM, "Jim Fleming" <[email protected]> wrote: >> >>> > Before you go too far down the path of CO2-climate sensitivity, please >>> > consider the work of Ed Lorenz who was interested in models that >>> > emulate sudden jumps from one equilibrium state to another, in >>> > patterns similar to the paleo-climatic record. >>> > >>> > In his paper "Climate is what you expect," Lorenz wrote: >>> > A climatologist encountering [fluctuations in real data] could not, on >>> > the basis of the data alone, say whether the dominant cause of the >>> > changes was external or internal. >>> > >>> > Elsewhere (climate of the model), for climate variations over a 100- >>> > year interval, as given by a simple one equation model designed to >>> > support internally produced climatic changes: >>> > >>> > "Two or more distinct climates may well be compatible with the same >>> > external conditions." >>> > >>> > Finally: >>> > "If the climate system is treated as a dynamical system--a system >>> > whose evolution is governed by precise laws, or, more frequently, by >>> > equations that represent such laws, the climate then becomes >>> > identifiable with the attractor of the dynamical system‹but the >>> > dynamical system may have more than one attractor!" >>> > >>> > Can we rely on single variable linear or logarithmic (non-chaotic) >>> > forcing to predict the future state of the climate system? >>> > >>> > Jim >> >> > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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/geoengineering?hl=en.
