The Greenhouse Effect Greenhouse gases are a natural part of the atmosphere. They trap the sun's warmth, and maintain the earth's surface temperature at a level necessary to support life. This is the enhanced greenhouse effect. Water vapour is the most important greenhouse gas, but human activities make little direct impact on the amount in the atmosphere.
Humans have most impact on carbon dioxide, methane and nitrous oxide.
Also making a relatively small contribution to climate change are various artificial chemicals such as halocarbons. Carbon dioxide emissions resulting from direct human activities have perturbed the global carbon cycle. Burning of oil, coal and natural gas, and the clearing and burning of vegetation, are the main causes of the rise. The digestive processes of cattle, rice cultivation, venting of natural gas, and waste decomposition in landfills are some of the major sources of CH 4 emissions. Australian scientists contribute significantly to the work of the Panel.