The Greenhouse Effect

Heat from the sun is trapped by greenhouse gases in the Earth's atmosphere - known as the greenhouse effect. Without this, the planet would be cold and lifeless. With too many greenhouse gases, the Earth would be intolerably hot, as is the planet Venus. Greenhouse gases, of which carbon dioxide is one, do therefore affect the climate; they are part of the Earth's climate system.

Contrary to what is stated by proponents of the man-made theory of Earth's recent warming trend, Earth's long history of changing climate is not mainly driven by carbon dioxide levels. In fact, temperature changes cause the level of carbon dioxide in the atmosphere to change, as indicated by the Earth's temperature record.

Is the man-made increase to atmospheric carbon dioxide levels likely to "tip the balance" and cause a "runaway greenhouse effect"? First of all, how much of the greenhouse effect is caused by carbon dioxide and how much is due to other greenhouse gases?

Carbon dioxide is a relatively minor greenhouse gas. By far the most important greenhouse gas is water vapour.

Furthermore, humans are not the main cause of carbon dioxide emissions. The oceans are responsible for most of it; as temperature increases, the equilibrium between dissolved carbon dioxide in the oceans and carbon dioxide in the air is shifted, and more carbon dioxide is released into the atmosphere. Dying vegetation, animals, bacteria and volcanoes all produce more carbon dioxide than humans.

It is not even clear that the greenhouse effect in general is a major factor in changing the Earth's temperature. Since the greenhouse effect occurs in the stratosphere, the theory predicts that temperature changes on the Earth would be greater in the stratosphere than in the atmosphere. However, studies have shown that recent temperature changes on the Earth have been more pronounced at the surface.