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.