Online Privacy

Although greenhouse gases make up only around 1% of the atmosphere (which is mainly nitrogen and oxygen), they have a significant influence on the Earth’s climate.  The main greenhouse gases linked to climate change are:

• Carbon dioxide (CO2) – responsible for about 60% of enhanced greenhouse effect.  Since the Industrial Revolution (c1780s) the atmospheric concentration of CO2 has increased by about 40% as a result of emissions from the burning of fossil fuels (gas, oil, coal etc.) to run vehicles, heat buildings and generate electricity.  The large-scale felling of trees has also added to CO2 levels by releasing the CO2 absorbed by the trees from the air during their growth.
• Methane (CH4) – responsible for 20% of the enhanced greenhouse effect.  Levels have more than doubled since the Industrial Revolution.  Methane is generated naturally by bacteria that break down organic matter in the guts of termites and other animals, but about two-thirds of global methane comes from man-made sources such as the burning of fossil fuels, drilling for natural gas and agricultural activities such as cattle ranching.  A molecule of methane is 21 times more powerful as a greenhouse gas than CO2.
• Nitrous oxide (N2O) – levels have increased by 16% since the Industrial Revolution and this gas is 200 to 300 times more effective at trapping heat than CO2.  The principal source of nitrous oxide is the use and leaching of nitrogen fertilisers on agricultural soils, but the burning of fossil fuels and wood, and sewage treatment plants, are other major contributors.  Road transport is a minor but growing source of nitrous oxide – particularly petrol cars with 3 way catalytic converters.
• Halocarbons – these include several ‘families’ of gases called CFCs, HCFCs, HFCs and PFCs.  These gases are almost exclusively man-made, used as spray can propellants, solvents, cleaners and coolants.  PFCs are a by-product of aluminium smelting.  Halocarbons are very slow to break down in the atmosphere and the warming effect they produce ranges from 3000 to 13000 times that of CO2.  Although the concentration of CFCs is stabilising following controls on their use through the Montreal Protocol (because of concerns about their effect on the ozone layer), other halocarbons are increasing.
• Sulphur hexafluoride – this is a man-made chemical that doesn’t occur naturally.  Its main use is as an electrical insulator in transformers and switchgear, but it is also used in tennis balls, some vehicle tyres and in the soles of some sports footwear.  It has a very long life in the atmosphere and a warming potential 23,000 times that of CO2, but its very low concentrations means that its contribution to the enhanced greenhouse effect is small.
• Water vapour – although this is the biggest contributor to the natural greenhouse effect it is not implicated in human-induced climate change, and human activities have very little impact on the level of water vapour in the atmosphere.  Its relevance to climate change stems from its capacity to magnify the effects of increases in the other greenhouse gases and produce a positive feedback effect.