Greenhouse gases and consequences
Greenhouse gases and consequencesGreenhouse Effect
The greenhouse effect is a natural phenomenon that warms the earth and enables it to support life. Without it, the average temperature on earth would be around -18 degrees C, instead of the current +15 degrees C - a frozen wilderness. It works on the same principles as the ordinary glass garden greenhouse, where glass allows light to get in, but does not allow for the heat to get out. This makes for a much higher temperature inside the greenhouse.
On a planetary scale, similar processes occur. Light from the sun has no trouble penetrating the atmosphere and reaching the earth's surface, warming it. The earth re-radiates much of this heat in the form of (invisible) infrared radiation. Infrared rays have a longer wavelength than visible light, and for this reason can be absorbed by certain gases in the atmosphere, labelled greenhouse gases. This absorption of heat warms up the atmosphere, which in turn radiates some of the heat back to the earth.
Greenhouse gases include water vapour, carbon dioxide (CO2), methane (CH4), chloroflurocarbons (CFCs), Ozone (O3), and Nitrous Oxide (N2O).
It all seems very straightforward: greenhouse gases trap the sun's heat, warming the planet sufficiently for life to exist. There is, however, one problem: human activity has dramatically increased the amount of greenhouse gases in the atmosphere.
Over the last two centuries the concentration of greenhouse gases in the atmosphere has increased quite significantly, mainly as a result of burning fossil fuels for industrial purposes. For example, atmospheric concentrations of carbon dioxide have increased from 280-285 parts per million in 1800 to 350 parts per million today. Currently the concentration of CO2 is rising by 0.4% per year. Methane has increased from about 750 parts per billion to 1700 parts per billion over the past 200 years, and nitrous oxide appears to be increasing at a rate of about 0.3% per year.
As the various greenhouse gases accumulate in the atmosphere, the amount of infrared radiation that is trapped increases. It is estimated that if we continue at our current rate of CO2 emissions alone, the average global temperature will rise by 1.5 to 4.5�C over the next 40 to 50 years.
Although the most important cause, burning of fossil fuels is not the only cause of the build-up of greenhouse gases in the atmosphere. Other causes include deforestation (trees absorb carbon dioxide, turning it into oxygen), the use of fertiliser (a source of N2O), and rotting organic matters (which produce methane).
Because of the many factors involved in the process, it is extremely difficult to accurately forecast the effects of an average global temperature rise of, say, 3 degrees on the earth in general or on Australia in particular. It is, however, possible to make some points with a reasonable degree of certainty.
The sea level would rise anywhere between 30 and 150 cm. This is the result of two factors: a partial melting of the Antarctic and Greenland icecaps, and...
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