Global Temperature
The Big Picture
Global temperature is controlled by the
amount of solar energy absorbed by the planet, including the amount of energy
trapped in the atmosphere by the greenhouse effect. Water vapor is the
primary greenhouse gas, but carbon dioxide (CO2)
gas also contributes to the
greenhouse effect. The oceans are significant sources of both water
vapor and carbon dioxide gas. When increased solar radiation reaches
the earth's surface, the surface water temperature can be increased - resulting in more water vapor and dissolved gases (like CO2)
being released into the atmosphere. Burning of fuels (combustion), decomposition of vegetation
(decay) and breathing animals (respiration) also release CO2
into the atmosphere, but these releases are counterbalanced by the
removal of CO2
from the atmosphere by growing vegetation (photosynthesis), carbon
being trapped in the ground (fossil fuels) and the formation of carbonates
in the oceans (carbonate-silicate cycle).
In addition to water vapor, water droplets
(aerosols and clouds) also affect radiation as it travels through the atmosphere.
The Earth's Energy Radiation
Budget [source]
The Global Carbon Cycle [source]
Global Temperature
Some Technical Details
The amount of solar radiation reaching
the earth's surface is influenced by many factors. The
actual radiation given off by the sun changes with time (11-year sun spot
cycle, intense solar flares, etc.). Also, planetary factors that influence the
percentage of radiation that passes through the earth's magnetic field
(magnetosphere) vary with time. There appears to be a correlation
between the earth's varying geomagnetic activity and global
temperature.
[source]
[source]
Artist's rendition of Earth's
magnetosphere [source]
The earth's geomagnetic
activity, in combination with the sun's magnetic activity, influences
the level of cosmic rays reaching earth. Cosmic rays may influence cloud
formation in the earth's atmosphere. The water droplets in clouds (like
greenhouse gases) have a major impact on the flow of energy through the
earth's atmosphere. Clouds reflect short-wave radiation back into space
(solar shield cooling), and reflect long-wave radiation back to
the earth's surface (greenhouse warming).
[source]
Global Temperature Measurement
Researchers Question Validity Of A 'Global Temperature'
ScienceDaily
(Mar. 18, 2007)
— 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).
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