The mean is just mean

Let's play a game. Is it meaningful to average the weights of all professional football players? OK, is is meaningful to average the prices of all foods purchases at all grocery stores? How about all temperatures all over the world?

Discussions on global warming often refer to 'global temperature.' Yet the concept is thermodynamically as well as mathematically an impossibility, says Bjarne Andresen, a professor at The Niels Bohr Institute, University of Copenhagen, who has analyzed this topic in collaboration with professors Christopher Essex from University of Western Ontario and Ross McKitrick from University of Guelph, Canada....

"It is impossible to talk about a single temperature for something as complicated as the climate of Earth", Bjarne Andresen says, an an expert of thermodynamics. "A temperature can be defined only for a homogeneous system. Furthermore, the climate is not governed by a single temperature. Rather, differences of temperatures drive the processes and create the storms, sea currents, thunder, etc. which make up the climate".

He explains that while it is possible to treat temperature statistically locally, it is meaningless to talk about a a global temperature for Earth. The Globe consists of a huge number of components which one cannot just add up and average. That would correspond to calculating the average phone number in the phone book. That is meaningless....

If temperature decreases at one point and it increases at another, the average will remain the same as before, but it will give rise to an entirely different thermodynamics and thus a different climate.

Other discussions note, among other things, that global temperature calculations ignore much of the earth, since they are taken over land rather than over water.

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