Greenhouse Affect

The earth’s climate is predicted to change because human activities are altering the chemical composition of the atmosphere through the build up of greenhouse gases – primarily carbon dioxide, methane, and nitrous oxide.

Energy from the sun drives the earth’s weather and climate, and heats the earth’s surface. This causes the earth to radiate the energy back into space. Atmospheric greenhouse gases (water vapour, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat similar to the glass panels of a greenhouse.

Without this natural “greenhouse effect,” temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earth’s average temperature is a more hospitable 24 C. However, problems may arise when the atmospheric concentration of greenhouse gases increases.

Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%. Methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. Due to the concentrations increasing the heat-trapping capability of the earth’s atmosphere is enhanced.

Greenhouse gas concentrations are increasing. Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. Plant respiration and the decomposition of organic matter release more than 10 times the CO released by human activities; but these releases have always been in balance with the carbon dioxide absorbed by plant photosynthesis. What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Energy burned to run cars and trucks, heat homes and businesses are responsible for about 80% of society's carbon dioxide emissions and about 20% of global nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions. Estimating future emissions is difficult, because it depends on economic, technological, and institutional developments.

The Hole in the Ozone LayerDiscovery of the hole in the ozone layer showed that human activity has a major impact on Earth. The destruction of ozone in the stratosphere high above the planet's surface has been brought about as the result of the widespread use of chemicals, which under normal conditions are chemically inert and harmless.

Ozone occurs at all levels in the atmosphere, but most of it is found in the stratosphere, between about 15-50 kilometres above the Earth's surface. Even there it occurs in minute concentrations, but it plays a very important role. Ozone absorbs harmful ultraviolet radiation which is produced by the Sun. Ultraviolet radiation can damage cells of living things - plants, animals and people. Whereas small doses result in nothing worse than sunburn, larger amounts may cause cataracts or skin cancer, and can affect the growth of plants.

The breakdown of ozone has been caused by complex chemical reactions involving chlorine and bromine. The ozone is produced like this: O2(g) + UV radiation 2O(g) O2(g) + O(g) O3(g) Decomposition: O3(g) + UV radiation O2(g) + O(g) O(g) + O(g) O2(g) Although small amounts of these elements occur naturally in the stratosphere - for