SL103: What Controls the Earth's Temperature?
David Noel
<davidn@aoi.com.au>
Ben Franklin Centre for Theoretical Research
PO Box 27, Subiaco, WA 6008, Australia.
The Earth is a sphere, isolated in space
People claim that the Earth's temperature has increased in recent years, and it may well have. But popular ideas about what is meant by "temperature", and the factors which may affect it, are often wildly off the mark.
The thing is, the Earth is a globe largely isolated in space, and is subject to the normal laws of physics. The latter must be understood for any rational analysis of any of its characteristics.
Fig. SL103-F1. The Earth, a Globe in Space.
One of the major obstacles to popular understanding of scientific matters is the difficulty in grasping the scale of things -- things which are so small as to be irrelevant in the whole picture, and things which are so large as to overwhelm smaller factors. This is understandable. The scale of things can be much better understood if numerical values are attached to the various factors, as is done here. Surprisingly, in modern science explanation, this point is often forgotten.
When it comes to the Earth's Heat Content, this parameter is always dynamically balanced -- total inputs always equal total outputs. If, say, a new input such as the explosion of a hydrogen bomb occurs, all the relevant factors rebalance themselves. With a big enough new input, there may be a measurable change in temperatures. But the Earth instantaneously readjusts itself for this.
Energy inputs and outputs -- the heat cycles
By far the biggest daily source of energy received by the Earth is that from the Sun -- that is, sunlight in the visible spectrum and either side. Interestingly, only about half of our solar input is visible light, most of the rest is infrared, with tiny amounts of ultraviolet and other wavelengths.
In "Temperatures of the Earth -- a Globe in Space" [A], the sizes of the various inputs and outputs are given in BLU units, to make them more easily grasped. The average daily input of the Earth in radiation from the Sun is set at 1 million BLUs -- most people can visualize a million of something, say the number of dollars needed to buy a house.
All the other factors involved in our Temperature Balance are less than a million BLUs. Perhaps surprisingly, the next biggest after sunlight is Evaporation -- between a quarter and a half of our input from the Sun is used the same day, to evaporate water from our seas and other water surfaces. This evaporation has a strong cooling effect. It also moves a huge amount of energy from our waters into the atmosphere, and this energy powers our winds, rainstorms, cyclones, and other weather events.
Fig. SL103-F2. The Earth's Energy Inputs and Outputs.
Figure F2 includes estimates of most of the Earth's inputs and outputs. Although the daily solar energy input is put at 1 million, in fact the amount received on any one day depends on the date. This is because the Earth follows an elliptical orbit round the Sun, rather than an exact circle.
Variation of solar energy received at different times of the year
On January 3, Earth is closest to the Sun, and on July 4, it it is most distant. This has quite a large influence on the solar input -- some 7 %, or 70,000 BLU. This variation in the amount of energy is close to 10 times the total amount of energy in any other factors, such as the amount of energy released from earthquakes each day.
The variation is close to 1000 times the energy used by Mankind each day. This is not just an interesting fact, it means that the amount of energy we use is insignificant compared to natural daily variations. It is arrogant for us to think we can can alter the Earth's temperature balance to any significant of measurable degree.
The Earth is in dynamic temperature equilibrium
We have looked at details of energy inputs, what about outputs, how does the Earth dispose of energy? All but a very tiny fraction of the energy that the Earth eliminates each day is Radiation, heat energy radiated away, mostly in the infrared.
The radiation from a body in space is defined very exactly by radiation laws, part of established physics. The first of these is the Stefan-Boltzmann law, which gives the intensity of radiation emitted from a surface, and depends very strongly on the temperature of the surface. The second is Planck's radiation law, which gives the spectrum -- the spread of energy against temperature -- of radiation from a surface.
In the case of our Earth, most of the radiation comes from the solid surface, a little from the edge of the atmosphere, and is dependent on the effective temperatures of these surfaces. This radiation travels at the speed of light. The term "Greenhouse" implies a barrier to this radiation, but no such barrier exists.
An independent test of Greenhouse claims
Finally, there is an independent test of "Greenhouse" theories, that is, of whether or not Mankind's activities have affected the temperature of the Earth.
Whatever we do on Earth is unlikely to have any measurable effect on the temperature of the Moon. We can measure the temperature of a point on the Moon easily and regularly using a pyrometer (optical thermometer).
Comparing reference temperatures on Earth and Moon over time, it it will be apparent whether or not changes are reflected on both bodies or on only one. If changes on Earth are due to external factors, such as changes in the Sun's output, similar changes will be seen on the Moon. If changes on Earth have no parallels on the Moon, then they can fairly be attributed to Man's activities. This is dealt with more fully in [C].
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AOI articles with relevant evidence
[A]. Temperatures of the Earth -- a Globe in Space (a re-analysis with some surprising results) .
[B]. Finally, the True Origin of Earthquakes?,
[C]. CM605: Has Mankind altered Earth's Temperature? (A decisive test for man-made global temperature change: The Reality Check for Greenhouse).
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SL103 Commenced writing 2025 Mar 14. First version 1.0 on Web 2025 Mar 20.
