DEFEND FOR THE POOR CARBON
|2.0 Antarctic Ice Core Data|
|5.0 Heat Balance Mechanism||6.0 Further Interpretation of Ice Core Data||7.0 Coming Interglacial Peak Period|
5.0 HEAT BALANCE MECHANISM
Thermonuclear reactions namely nuclear fusion and nuclear fission are the two major sources of energy that govern all the activities in the Universe. In Solar System, the Sun is the major source of nuclear fusion energy to the Earth, while the Earth is the natural nuclear fission reactor.
The fusion energy from the sun (peak at visible range) reaches the Earth through radiation on the Earth surface that facing the sun. Part of the solar incident is reflected to space depending on the Earth albedo or reflectivity. The earth emits heat to outer space throughout the whole Earth surfaces regardless of day or night via long wavelength radiation.
The Solar Constant  is the amount of energy that falls on a planet, on a plane perpendicular to the rays of the sun. This constant is a function of the distance of the planet from the sun. The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1.366 kilowatts per square meter (kW/m²). The actual direct solar irradiance at the top of the atmosphere fluctuates by about 6.9% during a year (from 1.412 kW/m² in early January to 1.321 kW/m² in early July) due to the Earth's varying distance from the Sun, and typically by much less than one part per thousand from day to day.
Thus, for the whole Earth (which has a cross section of 127,400,000 km²), the power is 1.740×1017 W, plus or minus 3.5%. The solar constant does not remain constant over long periods of time, but over a year varies much less than the variation of direct solar irradiance at the top of the atmosphere arising from the ellipticity of the Earth's orbit. The approximate average value cited, 1.366 kW/m², is equivalent to 1.96 calories per minute per square centimeter, or 1.96 langleys (Ly) per minute.
The Earth receives a total amount of radiation determined by its cross section, but as it rotates this energy is distributed across the entire surface area. Hence the average incoming solar radiation, taking into account the angle at which the rays strike and that at any one moment half the planet does not receive any solar radiation, is one-fourth the solar constant (approximately 342 W/m²). At any given moment, the amount of solar radiation received at a location on the Earth's surface depends on the state of the atmosphere and the location's latitude.
The energy from both nuclear reactions heats up the Earth as illustrated in figure 5.1 below.
Figure 5.1 – The fusion energy from the sun reaches the Earth through radiation and partly reflected. The fission energy from the core of the Earth reaches the Earth surface through convection and conduction. The earth emits the heat to outer space from all surfaces via radiation.
Figure 5.2 – Fission energy from the core of the Earth reaches the Earth surface through convection and conduction.
Earth's internal heat mainly comes from heat produced by disintegration decay. The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232. At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.
Heat from the Earth core is transferred to the surface through few methods:-
The crust layer of the Earth acts as an insulator to the heat transfer from core to the surface. The heat released to the surface through crust layer is less than the heat generated by nuclear fission process. The generated heat then accumulates at the Mantle layer. When molten substances at Mantle layer accumulate enough energy, it activates volcanic eruption and numerous earhtquakes to release the heat to the surface.
From the interglacial cycle shown by the ice core data as indicated in figure 5.3, the heat balance on the Earth is NOT always heat gained. In fact, most of the time, the Earth undergoes heat loss and the temperature drops. For each cycle of interglacial, the heat gain period from the lowest to the highest temperature is short; while it takes longer time for the heat loss period from the highest to the lowest temperature. The average temperature is around -5.5°C.
Figure 5.3 – The orange circle indicates an interglacial cycle.
The solar energy has great influence on the surface temperature of the earth and affects the weather; it can be easily balanced up by blocking the incoming incident such as higher Earth albedo and higher ash contain in the Atmosphere. The small temperature fluctuation is caused by variation in solar energy as the solar constant may fluctuate slightly. Solar energy is not the major switch in triggering the interglacial period. In general and averagely, the heat gain from solar energy is LESS than the heat loss from the Earth.
The atmosphere acts as a thermal insulation between the Earth and the outer space where heat is released through convection and radiation. It keeps on the Earth warm so that the Earth is livable. Higher content of water vapour in the atmosphere reduces the heat rejection rate.
The thermal energy from the Earth has great influence below the Earth surface and affects the climate; this energy is difficult to be released, and slowly accumulated within the earth. The heat accumulation in Mantle layer of the earth increases the movement of the molten substances and encourages for volcanic eruption and tectonic plate movement. The Earth thermal energy constitutes the remaining portion of heat loss of the Earth to the outer space.
The heat balance mechanism is illustrated in figure 5.4.
Figure 5.4 – The Solar energy and Earth thermal energy heat up the atmosphere, ocean, land, glaciers and ice. Glaciers and ices melt to water and flow to rivers and ocean. Water from the ocean vapourizes to form water vapour and rises to the atmosphere. When water vapour cools down, it precipitates in the form of rain or snow, falls to the ocean, glaciers or ices. The heat from the Earth emits to the outer space via radiation.
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updated on 27-April-2010.
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