Rapid Climatic Variations
If we were to rank in importance the climatic phenomena we’ve been discussing, the existence of rapid climatic variations would be at the top of the list. Who hasn’t heard of the halting of the Gulf Stream or, wrongly, of a return to a glacial-like climate that would affect the regions that border the North Atlantic? The media have seized this image and it has even been portrayed in theaters; it is the theme of The Day after Tomorrow, a sci-fi thriller from 2005. Let’s be clear: this is science-fiction; the icing over of a large part of the United States in a few days is, fortunately, not at all realistic. But the first scenes in which a glaciologist is at work are seductive.
As we have already mentioned, the analyses carried out over the ice in Greenland are at the heart of this notion of rapid climate variation. This idea already had some followers before the first deep ice core drilling took place at Camp Century in northwestern Greenland. But the opinion that was very widely accepted in the first half of the twentieth century was that the climate could only change gradually. That our planet has lived a succession of glacial and interglacial periods was, for many scientists, a concept that was difficult to accept, but to suggest rapid changes was absolutely out of the question, if only because it takes time for a glacial ice sheet to form or to melt.
In the 1930s the study of pollen preserved in peat bogs and lakes in Scandinavia challenged what was believed up to that point: in those regions the end of the last glacial period was clearly marked by oscillations: an initial warming, which ended in a period named Allerod, was followed by a cooling around the period of the Younger Dryas (a name derived from the name of a flower from the Arctic tundra, Dryas octapetala). In 1955, a few years after its