The Enhanced Greenhouse Effect

The greenhouse effect is a naturally occurring process in the atmosphere, which allows Earth to be habitable.

As the sun's rays reach the Earth, some are reflected off the upper atmosphere straight back into space. Rays that pass through the atmosphere are either absorbed by the earth, oceans, plants and animals or are reflected back into space.
On this final route, clouds, water vapour, carbon dioxide and other greenhouse gases (methane, nitrous oxide and others) trap some of these reflected rays, keeping the sun's heat in while allowing the rest to pass out into space.

The enhanced greenhouse effect follows the same route but due to higher consecrations of greenhouse gases, especially carbon dioxide, due to human activities such as burning of fossil fuels, farming and land use changes, traps more of the re-radiated rays in the atmosphere, warming up the planet.

Greenhouse Gas Emissions by Sector

Carbon Dioxide

The present atmospheric concentration of carbon dioxide has not been exceeded for the past 650,000 years, and possibly not for 20 million years. Ice core records show that carbon dioxide levels in the atmosphere varied between 180 and 280 parts per million (ppm) due to glacial cycles. For the past 10,000 years global atmospheric carbon dioxide has been quite stable at between 260 and 280 ppm, and level at about 280 ppm from 1000 to 250 years ago.

However, since the Industrial Revolution, some 250 years ago, carbon dioxide concentrations have increased by more than a third (to approximately 380 ppm), nitrous oxide levels by about 19 per cent and methane concentrations have more than doubled.

The burning of fossil fuels by humans adds about 6.5 billion tonnes of carbon each year in the form of carbon dioxide. Land clearing, reduced soil humus and the erosion of topsoil account for one to two billion tonnes of carbon a year.

Proof that more carbon dioxide is being added to the atmosphere than removed is the fact that concentrations of the gas continue to rise. Once carbon dioxide "the main greenhouse gas increasing through human activity" is released into the atmosphere, it stays there for between 50 and 200 years, while methane, 20 times 'stronger' than carbon dioxide, stays in the atmosphere for 9 years.

Department of Climate Change -

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Last updated: 29 March 2011

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