Roy's Foggy Avenues

Up and Down the Foggy Avenues of my mind.

Saturday, April 21, 2007

On "Normal weather"

It should now be clear that the physical environment of northern North America has changed dramatically in the past 20,000 years. This environment was (and still is) a complicated and intricate system, powered by the sun and land, ice, freshwater, salt water, and atmosphere as its components. Even if it were lifeless, it would still be dynamic; the components would interact with one another. One of the most interesting aspects of this never ending change from the ecological point of view is that, over the time interval we are considering (and probably for the whole of the earth’s history), physical conditions on this continent (and everywhere else) have never repeated themselves.

At no time has there been a return to “things as they were.” It is true that there must have been times when average temperatures were similar to those at present. Thus, before the beginning and after the end of the warmer-than-now hypsithermal interval, the average annual temperature must, for a while, have been much the same as now. But in other respects, conditions would have been radically different, as there were still extensive ice sheets that would have cooled their immediate neighborhoods, and sea level was still about twenty-five meters lower than at present. Nor is it reasonable to assume that conditions on the ice sheets were the same as those in Greenland and Antarctica today. The North American ice sheets were at a much lower latitude; they did not experience months of winter darkness, and the altitude of the midday sun in summer was much greater.


From After the Ice Age: The Return of Life to Glaciated North America. By E. C. Pielou (University of Chicago, 1991) pp. 29-30

1 Comments:

Anonymous Anonymous said...

People should read this.

9:15 AM  

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