Keeping the Earth Warm - the Greenhouse Effect:

• The sun radiates energy, largely as visible light, and the Earth absorbs some of this energy
• Some of the energy that's radiated from the Earth's surface is absorbed by gases in the atmosphere, warming it
• The gases in the atmosphere that stop the infrared radiation from escaping are called greenhouse gases, which create the greenhouse effect

Which are the Greenhouse Gases?:

• Greenhouse gases include: carbon dioxide, methane, nitrous oxide and CFCs
• Methane is produced by anaerobic decay of organic matter in waterlogged conditions, for example in bogs and rice fields
• Decay of domestic waste in landfill sites and the decomposition of animal waste are other sources of methane
• It's also produced in the digestive systems of animals such as cattle and released when they expel gas
• Incomplete combustion of fossil fuels can also release methane
• Since pre-industrial times, the atmospheric con of methane has more than doubled
• A molecule of methane can absorb more infrared than a molecule of carbon dioxide - but doesn't stay in the atmosphere for as long
• In less than 12 yrs, methane molecules will have reacted with oxygen to form carbon dioxide and water, but methane is continually being made
• Methane emissions could be reduced through better waste recycling and by using it as a biofuel
• When methane burns and produces carbon dioxide and water vapour, one greenhouse gas changes into two less serious ones
• It would eventually have turned into these gases anyway, and the energy that comes from burning methane from waste can replace energy from fossil fuel
• Significant increases in carbon dioxide levels in the atmosphere, through processes such as burning fossil fuels, have been linked to changing temps

Does Increase Carbon Dioxide Cause Global Warming?:

• There is a high correlation between temp and carbon dioxide levels
• Before the industrial revolution (1750), changes in carbon dioxide level are the result of changes in the Earth's orbit around the sun, changes in solar radiation, and volcanic eruptions
• A rise in temp is followed by a rise in carbon dioxide released from the oceans, which causes further warming
• The rise in carbon dioxide since the industrial revolution didn't follow a rise in temp - the conc in 2007 (383ppm) is 37% higher than in 1750
• The levels of carbon dioxide will continue to increase rapidly if emissions aren't reduced
• The correlation between carbon dioxide levels and and temp doesn't prove that one causes the other
• However, there is so much scientific evidence supporting the link between global warming and rising levels of greenhouse gases that it's now a widely accepted theory