Carbon dioxide is a naturally-occurring gas produced by nearly all forms of oxygen-related combustion. These forms of combustion include the burning of food by animals as well as the burning of fossil fuels such as oil and gas. Carbon dioxide is harmless in normal concentrations. When atmospheric levels rise significantly, they contribute to greenhouse effect.

Carbon monoxide is as invisible and odorless as carbon dioxide, but is far more harmful to the environment. This substance is produced primarily by the incomplete combustion of fossil fuels. Healthy animals breathe out little or no carbon monoxide.

Both carbon dioxide and carbon monoxide are greenhouse gases. Well-maintained vehicles produce negligible amounts of carbon monoxide, but there is no effective way to reduce carbon dioxide emissions from fossil fuel consumption other than reducing consumption of those fuels. Carbon monoxide is far more toxic to humans than carbon dioxide, but carbon dioxide plays a far greater role in greenhouse effect than carbon monoxide because it is produced in far greater quantities.

See also: