The greenhouse effect

Greenhouse gases are a natural part of the atmosphere. They absorb and re-radiate the Sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life. The problem we now face is that human actions—particularly burning fossil fuels (coal, oil and natural gas), agriculture and land clearing—are increasing the concentrations of the gases that trap heat. This is the enhanced greenhouse effect, which is contributing to warming of the Earth.

Greenhouse gases include water vapour, carbon dioxide CO2, methane, nitrous oxide and some artificial chemicals such as chlorofluorocarbons (CFCs). Water vapour is the most abundant greenhouse gas. Its concentration is highly variable and human activities do not directly impact on its amount in the atmosphere. The concentrations of the other greenhouse gases in the atmosphere are directly influenced by human activities. Once released into the atmosphere, many of these gases remain there for a long time.

The Greenhouse effect versus the enhanced greenhouse effect. In the greenhouse effect, the Earth is covered by a blanket of gases which allows energy from the sun to reach the Earth's surface, where some of it is converted to heat energy. Most of the heat is re-radiated towards space, but some is re-radiated towards the ground by greenhouse gases in the atmosphere. This is a natural effect which keeps the Earth's temperature at a level necessary to support life. In the enhanced greenhouse effect, human activities are generating more greenhouse gases. Greater concentrations of greenhouse gases will trap more heat and raise the Earth's surface temperature.