Interstadials in the Ice Ages

24 January 2014
Geology

This debate began at Anthony's site, Watts Up With That, some time ago, after the publication of a climate paper that made a great deal of the discovery of mosses that had been under the ice since an interstadial dated 43.5 to 39 thousand years ago. According to EM Smith (see http://chiefio.wordpress.com/2014/01/23/of-interstadials-a-fondness-of-b…) this implies it must have been warmer then than it is now – during an interstadial smack bang in the middle of the last 100,000 year Ice Age. The general opinion of climate scientists is that it was a little cooler rather than warmer – after all, there was no high in co2 or cows letting off wind in the alley behind the weather station.

Clearly, there could have been no ice when the mosses were growing. Unless they have got their dates wrong, which is I suppose a possibility, we have a very warm period around 40,000 years ago. This is roughly the period of the Chauvet cave art, which depicts lions in a savannah environment in the heart of Europe. The paper did not play on the fact it must have been warmer at that time, but concentrated only on the fact that it was so warm in the present world it was unearthing mosses that had lain buried for 40,000 years. Neither did they have much to say about the location in the middle of the so called Ice Ages.

Beetles can tell you a lot about temperatures in the past. SA Elias of Holloway College, University of London, situated on the A30 climbing out of Egham, an imposing building on the slope, in a paper in 2007 at http://pure.rhul.ac.uk/portal/files/17443513/Beetle_reveals_Late_Pleisto…, mentions that between 65 and 25 thousand years ago isotopic data from Greenland ice cores and N Atlantic sea bed sediment cores show multiple abrupt climate changes during the Marine Isotope Stage 3. The analysis of beetle assemblages in many parts of N America allow a reconstruction of the timing and intensity of climate changes (Elias, 1999). Some places were notably warmer than they are today. The warm period around 43.5-39ka coincided with the Upper Warren Interstadial in Britain between cooler Heinrich events 4 and 5. The latter was followed by another short interstadial around 33 thousand years ago – before temperatures plunged once again after a couple of thousand years. This was just prior, we may note, to the Late Glacial Maximum. It seems that Greenland ice cores show up 24 interstadials during the last 100,000 years (generally depicted as a cold and unpleasant period related to cycles in the orbit of the Earth). These are designated Dansgaard-Oeschger events (named after two Danish scientists).

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