Carbon dioxide (CO2) is an important greenhouse gas. Its presence in the atmosphere helps keep the Earth's surface warm. An increase of CO2 levels in the atmosphere will increase the Earth's surface temperature. In addition to this important physical role, CO2 affects climate through chemical reactions. For example, CO2 can mix with rainwater to form carbonic acid, which can cause chemical weathering of rocks. During photosynthesis, plants absorbs CO2 to produce plant tissues for the growth of plants.

Carbon monoxide (CO) is an air pollutant. It is a poisonous gas, which can cause death by demaging the central nerve system. It is a major product of the incomplete combustion of carbon and carbon-containing compounds. For more info, see below.

What's the Problem?
CO is an odorless, colorless gas that can cause sudden illness and death. Carbon monoxide is found in combustion fumes, such as those produced by cars and trucks, small gasoline engines, stoves, lanterns, burning charcoal and wood, and gas ranges and heating systems. Carbon monoxide from these sources can build up in enclosed or semi-enclosed spaces. People and animals in these spaces can be poisoned by breathing it.

The most common symptoms of carbon monoxide poisoning are headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion. High levels of carbon monoxide ingestion can cause loss of consciousness and death. Unless suspected, carbon monoxide poisoning can be difficult to diagnose because the symptoms mimic other illnesses. People who are sleeping or intoxicated can die from carbon monoxide poisoning before ever experiencing symptoms.