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Global Warming, Greenhouse Gases and Carbon Sinks

A brief, simplified explanation of phenomena which many people deny exist.

Why Global Warming and is it bad?
The sun's energy enters the atmosphere and energy is also radiated out into space. The energy rays, in and out, occupy different parts of the spectrum but they become effectively the same in that they add or remove heat, respectively. Once a balance has been established the rates of the two flows of energy are equal. However, part of the equation depends on the fact that some gases (greenhouse gases, see below) reflect back a proportion of the energy which would be outgoing, so temperatures on earth are warmer than would be the case otherwise. Intrinsically this is a natural phenomenon and is not bad, indeed it is the reason for life on earth, but the balance must be maintained when the temperature has reached this beneficial level for conditions to remain stable.
The gases which are produced by human activity may be small when considered as a proportion of the total gases produced by natural means but the balance can be likened to a knife edge and small percentage changes are important. Man-made emissions are increasing the greenhouse components to the extent that the balance is being upset and the earth is getting warmer and it is happening at a relatively fast rate. Recent research indicates that secondary effects are giving rise to positive feedback (where the warming itself indirectly leads to more warming). This is confirmed by meteorological data and observable natural events such as the shrinking of the icecaps, thawing in permafrost zones, rising sea levels and extremes of weather conditions.
While the average change is that of warming, local effects can include cooling because of the perturbations in the forces which drive our weather patterns. Other apparent contradictions include unprecedented floods in some areas but droughts in others. At present the impact seems minor (except to those individuals directly affected) but the eventual results will be widespread and deadly. It is already too late to stop many of the tragic outcomes of our excesses but a concerted global effort to limit the creation of further greenhouse gases could delay and mitigate the worst scenarios.
  Are there any other effects from gases?
Yes. In addition to the greenhouse gases there are some fluorocarbons (FCs; see HFCs and PFCs below) which deplete the ozone layer and allow harmful UV rays to reach the earth's surface, endangering life. The ozone layer forms a protective shield which is vital to many life forms including man. Although this appears to be a separate issue, there is a connection because the ozone depleting gases also contribute to global warming.
Sulphur Dioxide; SO2  is well known for its damaging potential to humans and trees especially. It is emitted mainly when fossil fuels are burned and, perhaps because its damage potential has been recognised for so long, its emission has been significantly controlled by clean-air acts. The immediate effects of SO2 are to cause urban fog, to cause respiratory complaints, and to produce acid rain and subsequent deforestation.

What are the greenhouse gases?
Well we're not covering the whole gamut but here are the six which are generally agreed to be the most important:
  • Carbon Dioxide; CO2
    This gas is produced naturally but careful tests show that human activity is responsible for very significant increases since the industrial age. Carbon dioxide is a by-product of the combustion of oil, gas, coal, wood (hydrocarbons) and can obviously be identified with vehicle exhausts, coal fires etc. Don't be fooled however, when you toast that slice of bread or boil the kettle, the apparently clean electrical energy comes from the power station which may be burning coal, oil or gas.
  • Methane; CH4
    Produced naturally, for example by rotting vegetation and flatulent cows, yaks and termites, methane is added to by human activities in the production and transport of coal, gas and oil and from rotting in landfill sites.
  • Nitrous Oxide; N2O
    Produced by industry and agriculture and during combustion of waste and fossil fuels.
  • Hydro fluorocarbons and Per fluorocarbons; HFCs and PFCs
    These are part of a group of compounds, containing fluorine in their make up, which have a very strong heating effect as well as depleting the ozone layer. CFCs have been used (unfortunately still are, in some devices) for pressurised sprays and refrigerants for example. It is hoped that they will eventually be banned worldwide. Some of the FCs are released in industrial processes.
  • Sulphate hexafluoride; SF6
    This gas is identified because of its extremely strong greenhouse effect. To see how much stronger it is than CO2, see the next paragraph.
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  Global Warming Potential of Different Gases
The ability for these gases to warm the atmosphere depends on two things. First, and perhaps most obvious, is the amount released (eg weight in tons or tonnes) but secondly, each of the gases has different greenhouse effects and is given a coefficient known as the Global Warming Potential (GWP). The normal reference is Carbon Dioxide for which the GWP is 1. By comparison the GWP for Methane is 21, Nitrous Oxide 310, most of the FCs are up in the 1000s with Sulphur hexafluoride at the top with a whopping GWP of 23,900.

What are Carbon Sinks?
Sinks are the opposite of Sources. Instead of releasing carbon into the atmosphere as is done when fossil fuels or wood are burned, sinks absorb carbon and lock it in. The most obvious examples are trees and other plants. As long as they are growing they are absorbing and fixing carbon (and some hold the opinion that the younger trees sink more carbon than old ones).

What Can the Individual Do to reduce Global Warming?
Well its spelled out above. Leaving aside the factors which are not easy to control such as political and industrial processes, the individual can minimise their consumption of energy derived from fossil fuels by, for example, reducing the amount of domestic heating and lighting, travelling shorter distances in cars, reusing items rather than discarding them, growing your own food or at least using locally grown crops, recycling waste, avoiding cutting and burning trees and where possible planting fresh trees.
And by the way the world is running short of water, especially drinking water; don't waste it!

Some of the above is derived from the US Environmental Protection Agency. To go to the EPA site click here.


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Originated: November 2000. Updated: 8 May, 2013