medieval-atlas/introductory/21

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Climatic changes Prelude The era in which we live seems to be merely one of the many interglacials which have temporarily intervened in the Quaternary Ice Age which has occupied most of the last 2.6 million years. Indeed, the ten thousand years of the present 'post-glacial' period probably passed its best over five thousand years ago, in its climatic optimum. Scotland came close to the reestablishment of glaciers during much of the medieval and postmedieval period. In many parts ofthe world, glaciers did in fact reassert themselves and this has become known as "the Little Ice Age". Early medieval warm phase The last really warm phase before the onset of the Little Ice Age ran from about AD 970 towards 1200, with much of the world perhaps at times approaching the warmth of the Climatic Optimum of approximately 5000 to 3000 BC. This amelioration would certainly have affected Scotland, since in Norway corn was grown to almost 70° north from AD 880 until the eleventh century. There were vineyards in England, and in many parts of Britain tillage was extended uphill to greater heights than for some time previously or since: Kelso Abbey for example had a grange at 300 metres (about 1000 feet), with over 100 hectares of tillage. Complex end of the warm phase The way that the warm phase ended demonstrates that it is an oversimplification to expect changes to involve mere north-south shifts in temperature zones. Thus, though the warm phase passed its peak: in Greenland in the twelfth century, it probably persisted in Europe until 1300 or 1310, though with an increase in severe storms affecting the North Sea, with sea-storm flooding on the low-lying coasts. The warmth may even have reached its maximum at this late stormy stage, for there is some evidence that in the 1280s tillage reached notably high levels. This would be meteorologically consistent, suggesting a strong outward thrust of the Arctic regimes in the longitudes of Greenland and Iceland, distorting the pattern of the circumpolar vortex with a sharp salient there being balanced by a recurrent warm sector over western Europe. This type of change is illustrated N.B. The Little Ice Age begins Soon after 1300 the cooling trend abruptly began to affect Europe. In Scotland the growing season was shortened, perhaps typically by three weeks or more; the accumulated warmth for growing and ripening crops decreased; and the frequency of harvest failures increased. The Little Ice Age was underway worldwide, and, though there were' some significant intermissions, it can be said to have continued right up to Victorian times. The greater part of the fifteenth century was a time of frequent cold winters and wretched summers. Within the last thousand years, only the 1690s seem to have produced so many severe winter spells within the span of one decade as the 1430s. An early sixteenth century intermission Evidence widespread round the world suggests some amelioration at the beginning ofthe sixteenth century. Scotland seems to have benefited from the rather frequent anticyclones affecting the latitudes 45° to 50° north, with westerly winds bringing the moderating influence off the waters of the North Atlantic Drift into northern Europe. The effect was warmth approaching that of the post-Little Ice Age phase of the first half of the twentieth century. This ended suddenly. The winter of 1564-6 exceeded in length and harshness any winter since the 1430s. r:"",::""/i''/. / "/ ;;; \ .... 'i\~'-I ....' , ......... / 1..... .... .. / .... 1\ ...... ' -'-',-f t, .... , .... ... ";I'-~''''.... ,/./\1 . /'/'-,'1, \l..,II~~~ -~/ ~ Sea ice ~. Little Ice Age ..., .,.-,., • ,IJ lAM

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