Text 27928, 93 rader
Skriven 2007-03-19 22:37:00 av Jeff Binkley (1:226/600)
Ärende: Global Warming
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http://www.sciencedaily.com/releases/2007/03/070315101129.htm

Researchers Question Validity Of A 'Global Temperature'
It is generally assumed that the atmosphere and the oceans have grown 
warmer during the recent 50 years. The reason for this point of view is 
an upward trend in the curve of measurements of the so-called 'global 
temperature'. This is the temperature obtained by collecting 
measurements of air temperatures at a large number of measuring stations 
around the Globe, weighing them according to the area they represent, 
and then calculating the yearly average according to the usual method of 
adding all values and dividing by the number of points.

Average without meaning 

"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. Or talking 
about economics, it does make sense to compare the currency exchange 
rate of two countries, whereas there is no point in talking about an 
average 'global exchange rate'.

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. If, for 
example,  it is 10 degrees at one point and 40 degrees at another, the 
average is 25 degrees. But if instead there is 25 degrees both places, 
the average is still 25 degrees. These two cases would give rise to two 
entirely different types of climate, because in the former case one 
would have pressure differences and strong winds, while in the latter 
there would be no wind.

Many averages 

A further problem with the extensive use of 'the global temperature' is 
that there are many ways of calculating average temperatures.

Example 1: Take two equally large glasses of water. The water in one 
glass is 0 degrees, in the other it is 100 degrees. Adding these two 
numbers and dividing by two yields an average temperature of 50 degrees. 
That is called the arithmetic average.

Example 2: Take the same two glasses of water at 0 degrees and 100 
degrees, respectively. Now multiply those two numbers and take the 
square root, and you will arrive at an average temperature of 46 
degrees. This is called the geometric average. (The calculation is done 
in degrees Kelvin which are then converted back to degrees Celsius.)

The difference of 4 degrees is the energy which drives all the 
thermodynamic processes which create storms, thunder, sea currents, etc.

Claims of disaster? 

These are but two examples of ways to calculate averages. They are all 
equally correct, but one needs a solid physical reason to choose one 
above another. Depending on the averaging method used, the same set of 
measured data can simultaneously show an upward trend and a downward 
trend in average temperature. Thus claims of disaster may be a 
consequence of which averaging method has been used, the researchers 
point out.

What Bjarne Andresen and his coworkers emphasize is that physical 
arguments are needed to decide whether one averaging method or another 
is needed to calculate an average which is relevant to describe the 
state of Earth.

Reference: C. Essex, R. McKitrick, B. Andresen: Does a Global 
Temperature Exist?; J. Non-Equil. Thermod. vol. 32, p. 1-27 (2007).


Note: This story has been adapted from a news release issued by 
University of Copenhagen.


Science Daily — 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.

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