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See-also: Flohn, 1974 and flohn in 1975

Flohn 1979: On Time Scales and Causes of Abrupt Paleoclimatic Events

Hermann Flohn: Quaternary Research, vol 12, p135-149, 1979. Another claim for the elusive "smoking gun"... but I don't think so. Before reading my views, lets read the abstract:

During the last 7 x 10^5 years the ocurrence of abrupt climatic variations, of an intensity probably reaching 5 oC/50 yr and with a duration of the order of several centuries can be demonstrated; their frequency is of the order 10^-4 (sometimes even 10^-3) per year. Most impressive examples are sudden coolings in earlier interglacials; in some periods the variability of past climates was obviously much greater than now. Due to the effective spatial coherence of the atmospheric and oceanic circulation their extension, not necessarily of similar intensity, is probably hemispheric or even global. They are modified by feedback mechanisms within the geophysical climatic system; orbital changes play a selective role leading either to suppression or to growth. Any physical interpretation of such abrupt palaeoclimatic events remain as yet speculative. One of the most attractive models is the occurence of clusters of major volcanic eruptions which is more frequent than expected in random series. This is similar to the clustering of severe earthquakes in recent years; both events are probably interrelated responses to the (apparently discontinuous) motions of tectonic plates.

Now, before discussing it as I should (which is to say, in terms of what was known when it was written) lets look at it in the light of todays knowledge. Or at least my present knowledge. First, I think the current view is that rapid changes don't occur during interglacials (e.g. [ 1] or perhaps [2] though I can't find a good ref for this). There *is* the 8.2kyr "event" but I gather that it is smaller than glacial D-O events and anyway probably related to the last draining of Lake Agassiz anyway. Note that current opinion is that both GRIP and GISP2 cores are unreliable for the Eemian. Second the volcanoes/earthquakes stuff I would discount - AFAIK the current view is that rapid change is caused by events associated with the Laurentide ice sheet. In retrospect, I think this paper probably fits into the discovery of rapid climate change.

Now moving on to the paper in its own time. Firstly, I still don't understand the coolings-during-interglacials claim: the examples he cites appear to be mostly at the end of the last glacial: the familiar Dansgaard-Oeschger events (which were beginning to be appreciated about when this was published). Its important for the predicting-ice-ages idea that he be talking about cooling events during an interglacial. He does have a section called "Examples of abrupt interglacial coolings", and particularly glacial stage 5e (127-115 kyr BP). I think this is still controversial, but how it was regarded at the time I don't know. Anyway, lets leave that aside for the moment. The argument in this paper is a shift from predicting full glacials towards predicting rapid coolings instead. From the point of view of predicting disaster, this is a step forwards, because getting a rapid ice age is and always was tricky: they are slow things.

As to whether this paper predicts anything, this from the abstract is relevant: Any geophysical interpretation of such abrupt palaeoclimatic events remain as yet speculative. So it looks like no predictions... but perhaps some speculation?

In the conclusion he writes:

From the viewpoint of a climatologist, the most imporant result of these investigations is the fact that within the human time scale of about 100 yr or less, our climate is (or can be in some periods) much more variable than hitherto assumed. Especially important, and indeed disquieting, is the evidence of abrupt cooling within warm (interglacial) periods, apparently as rare events with a recurrence time on the order of 10^4 yr. ... the last comparable events occurred ... during ... the Late Glacial (14,000 - 10,000 yr ago) ... Speculations about their geophysical mechanism have been made (above). The occurence of clusters of volcanic eruptions seems to be the most appropriate model, to be checked by further investigations... The problem of abrupt intense coolings during an interglacial climate similar to the present climate resembles, to some extent, the Damocles' sword hanging high above the globe and its inhabitants. Because of its possible consequences for the human race, its study deserves a much higher priority... this study can hopefully only serve as a trigger for a more serious treatment, including an assessment of risk.

So: I note that he finds these events rare (10^4 years apart) but they are disquieting. His best mechanism is volcanoes (which would presumably make predicting them difficult) and indeed he ends, after some Damoclean language, explicitly calling for further research.

My conclusion is that this is another there-are-risks-we-need-to-study-them paper.

Comments as ever welcome.

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