medieval-atlas/introductory/16

Transcription

Climatic processes With the predominant westerly winds bringing weather in off the Atlantic, the effect of the ocean on Scotland's climate is a profound but paradoxical one. Thus, despite a latitude reaching that of Greenland; warmth from the waters of the North Atlantic Drift keeps winters relatively mild. Yet in summer the heat-sink effect of the deep ocean holds down growing season temperatures, making crop ripening more marginal than in countries with more continental regimes, though these tend to have much more severe winters. Thus even southern Finland is better for ripening crops than much of Scotland. Also within Scotland, cereals ripen to much higher altitudes in the east, which is not only farther from the Atlantic heat-sink, but in the rainshadow of the mountains, with clearer skies. The shallow North Sea downwind is of much less climatic significance. Sandier soils in the east also dry out faster Greenland and warm up quicker in the spring. The flatter "oceanic" annual temperature curve in the west seriously reduces the amount of heat (measured in "accumulated day degrees") available above the threshold temperature needed for crops to grow. Thus, in contrast to the highpeaked curves of continental inlands, even a small change in conditions can be critical -whether due to climatic variations through time, or to altitude locally. Thus, vertical distances in, say, the Alps are of much less practical importance than in Scotland, and in particular, in Atlantic Scotland. There, even a small vertical change can severely constrain agriculture, while to ascend Ben Nevis from the relatively bland lowland at Fort William is to approach the climate of Greenland.

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