The greenhouse effect is a natural phenomenon. For millions of years, the levels of greenhouse gases in the atmosphere have remained relatively constant, part of a natural cycle that was regulated by the vast forests and oceans that covered the earth's surface. The atmosphere is the gaseous envelope that supports life on earth by providing chemicals necessary for life, protecting the earth's inhabitants from harmful solar radiation, and acting as a transport mechanism for heat, moisture and essential chemicals through the climate system. Air is a mixture of gases, primarily nitrogen and oxygen, with smaller amounts of water vapor and trace gases. While the others have remained constant, the level of greenhouse gases has risen dramatically over the last century.
Carbon dioxide is a gas that is vitally involved in the process of photosynthesis.
It is the most significant by volume of the gases presently responsible for the greenhouse effect. The cause of this increase is well known. Nearly all of it comes from burning fossil fuelscoal, petroleum and natural gas. A secondary source is deforestation. Because carbon is stored in trees, when they are cut or burned, carbon is released into the atmosphere.