Understanding Thermal Balance.

Heat is probably the most undervalued form of energy available to us. It is by far the most abundant form of energy occurring naturally, but most of it is left to dissipate to the surroundings as it will.

Our prime source of this energy is the Sun. This is a giant nuclear fusion reactor at a mean distance of some 93 million miles from Earth, Earth’s orbit taking us from a close point of 91.4 million miles to a far point of 94.5 million miles. The Sun is believed to be 4.6 billion years old already, and will continue to shine for a projected 7 billion years more.

Heat from the Sun reaches us in the form of radiation. The wavelength of this radiation is determined by the Sun’s temperature, which ranges from 16 million degrees K at the centre to 5,800 K at the surface, and the wavelengths range from Ultra Violet, and the visible spectrum, through to the short Infra Red.

The Ozone Layer in the Earth’s atmosphere fortunately blocks the worst of the Ultra Violet range, for these rays are very dangerous for us. The remaining radiation reaches the Earth’s surface, and is the driving force behind all life on the planet.

The composition of the atmosphere is crucially important to the thermal balance. Without Carbon Dioxide, or any other gas that would perform the same function, the temperature at the Earth’s surface would be about -18C, ie. the planet would be a ball of ice, and would stay that way. Some “greenhouse gas” is necessary for our continued existence.

The records of past planetary behaviour are held in ice cores, and detailed investigations of these records show that the Carbon Dioxide content of the atmosphere normally varies between two limits:- 200 ppm during an Ice Age, and 280 ppm during a warmer period.

Within these limits, the Earth is able to achieve thermal balance by re-radiating surplus energy out to space, and by storing energy in chemical form – fossil fuels. Note, however, that the balance is not a static one, but swings from one Ice Age to an Interglaciary period such as the one we are currently experiencing, and back again. Note also that energy directly re-radiated out to space is at a longer wavelength than that coming in from the Sun. This is because the wavelength of radiation is dependent on the temperature of the radiating object, and the Earth is much cooler than the Sun. This is what enables the “Greenhouse Effect” to function.

With Carbon Dioxide concentrations within this range, the condition of the planet is also influenced by other factors, such as its albedo (reflectivity), and periodic changes to external influences such as orbital forcing, as described in the Milankovitch theory.

With Carbon Dioxide concentrations above this range, however, changes in albedo will have a reduced effect. Temperatures will increase, and we see evidence that this is already happening. The fact that Olive trees will now grow in Southern England, (Devon), shows that a Mediterranean climate is now being experienced at a latitude of 51°N – hitherto unheard of.

We must also remember that the Earth has an additional heat burden to dispose of – the one caused by us using 80 million barrels of oil per day. We can no longer afford to just let this heat dissipate into the surroundings, for the surroundings themselves are in trouble, and this is where we live!

Further increases in temperature will trigger further effects that will accelerate the problem. The two most disturbing ones are the release of Methane from the Arctic Tundra, and the increase in Water Vapour take-up of the atmosphere in general. Both Methane and Water Vapour are greenhouse gases, and are considerably more effective than Carbon Dioxide.

As temperatures increase, water locked up as ice will melt. There is overwhelming evidence to show that this is happening around the world already. The immediate result of this will be higher seal levels, which in turn leads to decreased land area. As oceans retain more heat than land, there will be an additional warming factor added to the others. Increasing temperatures in the oceans themselves will in turn lead to further increases in sea level, compounding the problem still further.

If we are to get the Earth back into thermal balance, the task will be easier if we do it before further greenhouse mechanisms are triggered – and this means starting Carbon Sequestration now.

Our use of heat energy should be completely revised. Heat can be controlled with remarkably low technology – mirrors, conductors, insulators, heat engines, and it has no qualms about doing work on its way from its higher-temperature source to its lower-temperature destination. We have to learn to use it effectively, in as short a space of time as possible.

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3 thoughts on “Understanding Thermal Balance.”

  1. You note (correctly) that the additional heat burden released by the oil burned must also be re-radiated to achieve a thermal balance.
    I believe that the focus on CO2 has taken away from the importance of the entirity of the “thermal pollution” we generate. Further, the machaniasms of this pollution(i.e. direct thermal injection into the seas due water cooling of heat generating plants wghich increases the the H2O content of the atmosphere)) is of importance as well because it effects the kinetics of global warming, as opposed to the thermodynamics.
    I do not find sufficient attentioon to these matters in hte global discusstins. I suspect that even if we were to be stable today at 240ppm CO2, we would find our release of heat into the environment would cause global warming. I have not seen sufficient attention given it. We may need more fundamentally look at whether or not we can continue the modern rate of thermal pollution at all, regardless of CO2 emissions. Why are these more fundamental and , Ibelieve , larger problems, no even well publisized?

  2. Hello ML,

    I think a simple way of viewing this is to think of a water tank, which in this case represents the Earth, and an immersion heater, which represents the 80 million barrels of oil per day. In order to save energy, we usually lag the water tank with a special insulation jacket. This means that for a given water temperature, we use less energy, and save cost. If we use the same amount of energy with the insulation in place, the temperature of the water will be higher than it would be without the insulation.

    The Carbon Dioxide, and other greenhouse gases, are of course the insulating jacket.

    The complex way of looking at it is to use computer modelling, and many experts around the world are doing just that. Whenever they find something of significance, they publish their data, and this is the source of some of my information.

    An excellent, though alarming, recent publication is

    http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
    Climate Change and Trace Gases

    and I recommend that you take the time to read it thoroughly.

    An older document is well worth a read also. This is a sidebar in Microsoft Encarta entitled

    “The Dynamic Atmosphere”

    Having said that, your suggestion that “It could be 3 causing 1 right?” could well become correct. This will occur at the next stage, when trees stop being a net absorber of Carbon Dioxide, and become a net source of it over any 24 hr period.

    This is one of the escalations that I would very much like to forestall, for after it occurs, our task will be much harder.

    Futher increase in temperature after that will trigger an increase in Methane content as the Arctic Tundra thaws. At that point, as Methane is 21 times more effective than Carbon Dioxide at retaining heat, we need to sequester Carbon Dioxide at a much faster rate to compensate.

    The sooner we act, the better!

  3. I understand and accept the following statements as true:
    1-The CO2 concentration is rising
    2-CO2 absorbs parts of the infrared spectrum
    3-The temperature of the earth is rising

    My question is: how can be we be sure that 1 and 2 are *causing* statement 3? I am told we’re pretty sure that’s the case but I’ve never seen a proof of this link of causality.

    It could be 3 causing 1 right? or it could be mere correlation of 1 and 3

    ML

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