Posted: Monday, February 2, 2009 12:00 am
The most puzzling aspect of much of the climate-change reporting these days is the frequent reference to average or mean temperatures.
It's puzzling because there is no such thing as an average temperature in the real world, the world where weather happens and plants grow or don't grow. There is only the actual temperature at whatever time it is measured.
The other day scientists came out with a report that trees in the western United States were dying at roughly twice the rate as 50 years ago. During any one year now, 2 percent of the trees in any stand of forest were dying, compared to 1 percent at the beginning of the study period. The report related this change to an average temperature increase of 1 degree over the period.
It's hard to understand how a minuscule change in "average temperature" can affecting anything like a forest, especially tree species that lived through the last ice age as well as the 1930s, the hottest period on record.
Suppose its a freezing 20 degrees F at night and 70 degrees in the afternoon. The average for that day is 45 degrees. The next day it's 40 at night and 50 in the afternoon.
Completely different conditions, but the same average temperature. The effect of the weather on living things would be very different those two days, but according to the average, conditions were just the same.
And if "average" can means so many things, then how do scientists conclude that something or other happened because of a change in the average?
If tree mortality actually rose, relating it to the average doesn't say whether it rose because it was mostly hotter or mostly colder; or because the days were cooler and the nights milder or vice versa, or whether it had anything to do with temperatures at all. (hh)