Some years ago I purchased a slim volume, Reversals of the Earth's Magnetic Field, expecting some information that might bear on the subject Peter Warlow was researching. It didn't prove much help at the time but I have now had a second look at it. Written by professor JA Jacobs of Cambridge University (and formerly of the University of British Columbia) it was originally published in 1984. It is still available second hand on the ABE book site – simply log in the ISBN number, 0-85274-442-0. However, a later edition, in 1994, is selling at Amazon for silly money which is a pity as there is not a lot of useful information on geomagnetic reversals in the book that might inspire SIS members. It does show how closely the idea of magnetic reversals became bound up with the orbital cycles of Milankovitch and the idea of Ice Ages repeating themselves at 100,000 years or so. In that respect the book is useful as it is always illuminating to go back to the thought processes that dreamed up the major planks of science, and Plate Tectonics has become embedded in a quite firm manner and is rarely challenged. In that respect it is invaluable as it also throws up some flaws, problems that have been papered over in modern literature on Plate Tectonics. It is also interesting that a couple of recent magnetic reversals have been largely washed out of modern thinking on the subject. The so called Gothenburg Excursion and the Lake Mungo event. The latter was dated to around 30,000 years ago – smack in the middle of that huge C14 plateau.
The author explores a link between geomagnetic activity, the Sun, and climate (Ice Ages) and the Milankovitch cycle of eccentricity. As long ago as 1978 the link between sun spots and cycles was being seriously explored by some scientists, and solar cycles of 11 and 22 years. It was noted there was evidence for significant correlations between certain meteorological indices and the passage of the solar magnetic sector structures across the Earth (the solar wind interacting with the magnetosphere). I wonder if Piers Corbyn picked up some ideas from Jacobs?
Roberts and Olan (1973) suggested high latitude atmospheric ionisation played a role in nucleating cirrus clouds, pre-empting some of the ideas of Svensmark. Rhodes Fairbridge (1977) attempted to test such ideas at the Gothenburg Excursion, dated by Nils Axel Morner and Lanser (1975) as occurring between 13,750 and 12,350 years BP (what was then the date of the Younger Dryas Boundary event). The Excursion coincided with a short phase of glaciation during what had been a general melting environment. We may note that then, as today, catastrophism is never mentioned in the context of climate change. Jacobs also notes there was a fall in sea levels at this time which contrasted with the general rise in sea levels that had been going on since the end of the Ice Ages (as it is thought). This must be somewhere in Morner's published papers which wil be worth having a look at. The Gothenburg Excursion does not appear to have resulted in a full reversal of the Earth's magnetic field but it is interesting that on Peter Warlow's tippe top mechanism the process could have been temporary, falling back to where it began as a result of a partial inversion. Presumably Warlow was looking at geomagnetic reversals before he died as he is on record as saying that he may have picked some data up prior to the Holocene, having largely dropped the idea of Holocene reversals. His book, The Reversing Earth, is available from the SIS Book Service. Jacobs, however, goes on to say the Holocene is characterised by alternating intervals of glacial advance and retreat.