Dear Igor and Eric There are a couple of mooted causes of the Younger Dryas - discussed here.
http://www.ldeo.columbia.edu/res/pi/arch/main.shtml 'A problem with this hypothesis is the timing of meltwater pulses that are supposed to have triggered the THC shutdown: it was found that a second meltwater pulse, albeit slightly smaller than the first one, occurred at the end of the YD (Fairbanks, 1989): why didn't it also trigger a similar chain of consequences in the climate system? An alternate explanation (Clement et al., 2001) invokes the abrupt cessation in the El Nino -Southern Oscillation in response to changes in the orbital parameters of the Earth, although how such a change would impact regions away from the Tropics remains to be explained. (In fact ENSO has many global teleconnections - my note) The respective merits of both hypotheses have been laid out by Broecker (2003). The issue is far from being settled, and actively researched at Lamont and elsewhere.' Remembering the difficulties in paleoclimatic investigations - addressed well in the National Research Council Abrupt Climate Change - Inevitable Surprises. Problems that include the sparsity and intrinsic limitations of proxy data. Problems characterised by the NRC as listening to the evidence on a scratchy recording in a dark room. To quote from Alley Broecker et al. (1985) argued, “Until now, our thinking about past and future climate changes has been dominated by the assumption that the response to any gradual forcing will be smooth. But if . . . the system has more than one quasi-stable mode of operation, then the situation is more complex” (p. 25). The particular mode switch that Broecker et al. (1985) discussed was the “turning on and off of deep- water production in the northern Atlantic” (p. 24). THC is only one possible mode switch - I have listed a few of them from the Adams et al paper - and added a few. Alley also lists a few. Earth climate is a system with many degrees of freedom - concentrating on one or two and saying that everything is explained and therefore not chaotic misunderstands both the provisional nature of the paleaoclimatic evidence (and conjecture based on it but also the nature of chaos theory. ‘The climate system is particularly challenging since it is known that components in the system are inherently chaotic; there are feedbacks that could potentially switch sign, and there are central processes that affect the system in a complicated, non-linear manner. These complex, chaotic, non-linear dynamics are an inherent aspect of the climate system.’ (IPCC TAR s14.2.2.1 - http://www.ipcc.ch/ipccreports/tar/wg1/504.htm) 'The global coupled atmosphere–ocean–land–cryosphere system exhibits a wide range of physical and dynamical phenomena with associated physical, biological, and chemical feedbacks that collectively result in a continuum of temporal and spatial variability. The traditional boundaries between weather and climate are, therefore, somewhat artificial. The large-scale climate, for instance, determines the environment for microscale (1 km or less) and mesoscale (from several kilometers to several hundred kilometers)processes that govern weather and local climate, and these small-scale processes likely have significant impacts on the evolution of the large-scale circulation (Fig. 1; derived from Meehl et al. 2001). The accurate representation of this continuum of variability in numerical models is, consequently, a challenging but essential goal. Fundamental barriers to advancing weather and climate prediction on time scales from days to years, as well as longstanding systematic errors in weather and climate models, are partly attributable to our limited understanding of and capability for simulating the complex, multiscale interactions intrinsic to atmospheric, oceanic, and cryospheric fluid motions.' A UNIFIED MODELING APPROACH TO CLIMATE SYSTEM PREDICTION by James Hurrell, Gerald A. Meehl, Davi d Bader, Thomas L. Delworth , Ben Kirtman, and Bruce Wielicki: BAMS December 2009 | 1819: DOI: 10.1175/2009BAMS2752.1 You can't seriously argue that climate isn't chaotic. A bit of a flat earth stance - linear thinking in a nonlinear world - but not my problem. The second question was whether I agreed with Tsonis about a monotonic forced warming signal (of about 0.1 degee C/decade). A rate of warming that is much less risky - I might add - than the more common higher estimates based on simple trends in the surface temperature record alone. I have to admit that I don't know what it means. Global temps respond to external forcings - orbital, greenhouse gases, solar - granted but the response is nonlinear. So I don't think you can point to the temperature graph and say - this much is oceans, this much carbon dioxide, this much solar variations etc. There are changes in evaporation, convection, heat transport, precipitation, landscape, biology, winds, clouds, ice - some positve feedbacks, some negative, some switch signs and some are obscure (only a fool would think that everything is known in great detail) - but all acting as a total system and producing surprising results. In a nonlinear system with many degrees of freedom and therefore subject to frequent abrupt change - warming or cooling can and does happen fairly regularly by all the accounts of Anastasios Tsonis and Kyle Swanson. Greenhouse gases add to climate instability. Beyond that - I don't think a simple forced warming beyond the time scale (years to decades) of abrupt climate change is a useful concept. Cheers Robert Here is the link I left out for Earth albedo Figure 2: http://bbso.njit.edu/Research/EarthShine/literature/Palle_etal_2008_JGR.pdf On Jan 31, 4:12 am, Igor Samoylenko <[email protected]> wrote: > Eric Swanson <[email protected]> said: > > > Igor, are you responding to my post? > > Sorry Eric, I should have made it clear. > > My post was addressed to Robert. The first part was an elaboration on what > you said: > > "The Younger Dryas started with a well known single event, a flood of fresh > water related to the melting of the glaciers over Canada. That event is not > repeatable in the present situation, thus it is not partof some chaotic > oscillation, or what ever you are trying to claim it is. " > > The second part was a question for Robert. > > Eric Swanson <[email protected]> said: > > > I haven't read the paper in the PNAS by Kyle Swanson, et al., as it's > > behind a pay wall. But, from the information I've seen, it sure looks like > > the Earth is experiencing a warming trend. > > Indeed. I wanted to see if Robert agrees with Swanson and Tsonis that there > is "externally forced climate signal, which is monotonic, accelerating > warming during the 20th century". > > On Jan 30, 10:24 am, Igor Samoylenko <[email protected]> wrote: > > > > > It is not just Younger Dryas but also numerous other abrupt climate jumps > > during the last Ice Age cycle known as Dansgaard-Oeschger and Heinrich > > events are all thought to be linked to fresh-water fluxes and resulting > > disruption of North Atlantic deep water formation. There is a lot of > > literature on this topic, but here is a good summary paper: > > > Alley, R.B. Wally Was Right: Predictive Ability of the North Atlantic > > “Conveyor Belt” Hypothesis for Abrupt Climate Change. Earth and Planetary > > Sciences35, 241-272 (2007). > > http://shadow.eas.gatech.edu/~kcobb/abrupt/alley07.pdf. > > > "Linked, abrupt changes of North Atlantic deep water formation, North > > Atlantic sea ice extent, and widespread climate occurred repeatedly during > > the last ice age cycle and beyond in response to > > changing freshwater fluxes and perhaps other causes. This paradigm, > > developed and championed especially byW.S. Broecker, has repeatedly proven > > to be successfully predictive as well as explanatory with > > high confidence. Much work remains to fully understand what happened and to > > assess possible implications for the future, but the foundations for this > > work are remarkably solid." > > > Chris Turney has a whole chapter on this in his book Ice, Mud and Blood > > Lessons from the climate past. > > > As forTsonisandSwanson, you are of course aware of their recent paper: > > > Swanson, K.L., Sugihara, G. &Tsonis, A.A. Long-term natural variability > > and 20th century climate change. Proceedings of the National Academy of > > Sciences106, 16120-16123 (2009). > > http://www.pnas.org/content/106/38/16120.abstract > > > "Global mean temperature at the Earth's surface responds both to > > externally imposed forcings, such as those arising from anthropogenic > > greenhouse gases, as well as to natural modes of variability internal > > to the climate system. Variability associated with these latter > > processes, generally referred to as natural long-term climate > > variability, arises primarily from changes in oceanic circulation. Here > > we present a technique that objectively identifies the component of > > inter-decadal global mean surface temperature attributable to natural > > long-term climate variability. Removal of that hidden variability from > > the actual observed global mean surface temperature record delineates > > the externally forced climate signal, which is monotonic, accelerating > > warming during the 20th century." > > > So, do you accept that (having removed natural variability) we have > > externally forced climate signal, which is monotonic, accelerating warming > > during the 20th century? > > I haven't read the paper in the PNAS by Kyle Swanson, et al., as it's > behind a pay wall. But, from the information I've seen, it sure looks > like the Earth is experiencing a warming trend. I can't speak for > Robert... > > E. S. > --- > > -- > 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 > athttp://groups.google.com/group/globalchange -- 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. 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