From Envirowiki

Carbon dioxide (CO₂) is a chemical which makes up a large part of our atmosphere (currently 381 parts per million by volume). As a gas, it is a vital to carbon-based lifeforms, especially plants.

Carbon dioxide is an non-reactive greenhouse gas. It is produced by burning carbon (coal, fossil fuels, plant matter) in air or oxygen.

[edit] reducing carbon emissions

there are numerous methods proposed to reduce anthropocentric carbon emissions in the atmosphere. these include

• carbon trading schemes, in which industries are given carbon credits, and must buy more if they want to pollute more.
• contraction and convergence, when used with a carbon rationing system, gives all world citizens an equal allocation of carbon emissions, which can be traded. This means that those in the third world are able to continue to expand their carbon emissions for a short time, while rich citizen (high carbon users) must decrease their emissions quickly, or buy more rations from those who don't need them. rationing allows the emplacement of solid carbon emission targets
• carbon taxing. simple putting a tax, or a levy on all carbon produced for any production process. taxing is simple to police, but does not allow for targets.

[edit] see also

one tonne of carbon