Perspective by William McClenney on the paper of the same title by:
P. C. Tzedakis, E.W. Wolff, L. C. Skinner, V. Brovkin, D. A. Hodell, J. F. McManus, and D. Raynaud
I can often be heard, when assailed by the well-informed, climate, to ask the eminently reasonable question “In your opinion, how long will the Holocene last?” Rodney Dangerfield Syndrome then ensues, without exception so far, because astonishingly, few of the climate cognoscenti have even heard of the Holocene, much less pondered how, why, and by what mechanism it might, theoretically, be extended……
This IS the debate we should be having. So far, the Holocene has been quite the historically stable little interglacial, so far not exhibiting the normal climate instabilities of the typical end extreme interglacial.
But “Can we predict the duration of an interglacial?”
This, now week-old paper, explores a fascinating linkage concept, the inception and disintegration of the bipolar seesaw.
“We propose that the interval between the “terminal” oscillation of the bipolar seesaw, preceding an interglacial, and its first major reactivation represents a period of minimum extension of ice sheets away from coastlines.”
I will leave it to the experts to comment and debate as to whether or not we are perhaps seeing the onset of said bipolar seesaw in Arctic/Antarctic sea ice, and whether or not such is applicable in an anthropogenic greenhouse-gas world.
However, we might need to consider:
“…thus, the first major reactivation of the bipolar seesaw would probably constitute an indication that the transition to a glacial state had already taken place.”
As we work our way through this paper, we find:
“With respect to the end of interglacials, the MIS 5e– 5d transition represents the only relevant period with direct sea-level determinations and precise chronologies that allow us to infer a sequence of events around the time of glacial inception (Fig. 2).”
“Thus, glacial inception occurred ~3 kyr before the onset of significant bipolar-seesaw variability.”
“Given the large decrease in summer insolation over the Last Interglacial as a result of the strong eccentricity-precession forcing, we suggest that the value of 3 kyr may be treated as a minimum. We thus estimate interglacial duration as the interval between the terminal occurrence of bipolar-seesaw variability and 3 kyr before its first major reactivation.”
This paper then proceeds to get very deep indeed into the evolution of the post-MPT interglacials, with an eye towards how each might be relevant to our interglacial times.
The take-home context, in terms of CO2 forcing might be encapsulated by this:
“A corollary of all this is that we should also be able to predict the duration of the current interglacial in the absence of anthropogenic interference. The phasing of precession and obliquity (precession minimum/insolation maximum at 11 kyr BP; obliquity maximum at 10 kyr BP) would point to a short duration, although it has been unclear whether the subdued current summer insolation minimum (479Wm−2), the lowest of the last 800 kyr, would be sufficient to lead to glaciation (e.g. Crucifix, 2011). Comparison with MIS 19c, a close astronomical analogue characterized by an equally weak summer insolation minimum (474Wm−2) and a smaller overall decrease from maximum summer solstice insolation values, suggests that glacial inception is possible despite the subdued insolation forcing, if CO2 concentrations were 240±5 ppmv (Tzedakis et al., 2012).”
Would you like fries with your Baked Alaska?
I have sent Anthony the raw and highlighted versions. A bloody good read.
cp-8-1473-2012 (PDF raw)
cp-8-1473-2012 HLT (PDF highlighted)