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 a warming of the earth’s surface. Water vapour is the most abundant greenhouse gas. Its concentration is highly variable and human activities have little direct impact on its amount in the atmosphere. Humans have most impact on carbon dioxide, methane and nitrous oxide. Various artificial chemicals such as halocarbons also make a small contribution to the enhanced greenhouse effect.

The Greenhouse Effect

The Greenhouse Effect

The Enhanced Greenhouse Effect

The Enhanced 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.

Human activities – particularly burning fossil fuels (coal, oil and natural gas), agriculture and land clearing – are generating more greenhouse gases. Greater concentrations of greenhouse gases will trap more heat and raise the Earth’s surface temperature.