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The Climates of the Geological Past

kgrsadghogrAAll geologists will have heard of Alfred Wegener. Few will have heard of his father-in-law, Wladimir Köppen, one of the founders of modern climatology. In his early work Wegener applied the principle of the primacy of climatic zones to reconstruct continental positions through time, capitalizing in a way on Lyell’s notion that a shifting of the continents across climate zones might explain the global distribution of fossils and the location of past climate-sensitive deposits. Meeting Köppen, whose climate classification system matches temperature and precipitation to patterns of vegetation and soils, and who was much taken with Wegener’s ideas, Wegener found an ideal collaborator.  Their magnum opus was published in German in 1924. It featured the first comprehensive suite of global palaeoclimatic maps (displaying the distributions of climate sensitive indicators) for the Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Eocene, Miocene, and Pliocene + Early Quaternary, all made without the benefit of palaeomagnetic observations. Salt and gypsum deposits were found to be common where such evaporites are found today, in the arid belts north and south of the equator. Cretaceous corals characterized the equatorial zone between the 30th parallels, just like today. Glacial indicators clustered around the poles. And coals occurred under temperate humid conditions, and in the humid tropics.

In the 1930s, Alexander Du Toit enthused about Köppen and Wegener’s concepts, which enabled him to predict where past climate zones were. But widespread influence was handicapped by the lack of an English translation. Perhaps as a result, Köppen does not feature in the index to Arthur Holmes’s magisterial Principles of Physical Geology, 1965. Not until palaeomagnetic data made continental reconstructions accurate, beginning in the 1970s, did we see, a resurgence of the Köppen and Wegener approach in the palaeoclimatic maps of Pamela Robinson at UCL, fast followed by the efforts of Fred Ziegler and Judy Parrish at the University of Chicago.

For their Quaternary chapter, Köppen invited a contribution from Milutin Milankovitch, who had just begun using celestial mechanics to explain climate change over the past 65,000 years. Köppen saw that Milankovitch’s coolest periods matched the sequence of 4 glacial and 3 interglacial events found by Penck and Bruckner in the Alps. Milankovitch graciously allowed the use of his published calculations in the book, and added some new unpublished features. As the book’s editors point out, this made it possible for the first time “to establish a precisely defined time scale of Late Cenozoic glacial-interglacial history”. Where Köppen and Wegener went wrong was in thinking that differences in the positions of the fronts of past ice sheets in Europe might also reflect the wandering of the Quaternary pole, whose positions would not be established by palaeomagneticists for another 25 years. Even so, they did make clear for the first time that the peak of the last Ice Age - the Last Glacial Maximum – occurred about 20,000 years ago. Köppen, the great climatologist, convinced Milankovitch that the key to creating a glaciation was the duration of summer warmth, not winter cold. Milankovitch’s data showed that the latest peak in insolation and summer warmth occurred about 10,000 years ago. Since then, Köppen reasoned, orbital change cooled northern hemisphere summers – a process that is still going on today.

Despite the limitations imposed on their data by a paucity of samples and the crude state of geological dating, their product has stood the test of time. It is now a historical masterpiece and well worth the purchase.

Reviewed by Colin Summerhayes

THE CLIMATES OF THE GEOLOGICAL PAST / DIE KLIMATE DER GEOLOGISCHEN VORZEIT by Köppen, W., and Wegener, A., Borntraeger Science Publishers, Stuttgart 2015, edited by J. Thiede, K. Lochte and A. Dummermuth. ISBN 978-3-443-01088-1.W: