The following is a news release from the University of Copenhagen
this past March. I've decided not to put it in my own words
because I agree with Professor Andresen, and want the
article to reflect his views rather than mine because he is the
professor not me.
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 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).
http://www.sciencedaily.com/releases/2007/03/070315101129.htm
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