Causes

• Carbon dioxide

Of the greenhouse gases, carbon dioxide (CO₂) is the most significant. Natural sources of atmospheric CO₂ include outgassing from volcanoes, the combustion and natural decay of organic matter, and respiration by aerobic (oxygen-using) organisms. These sources are balanced, on average, by a set of physical, chemical, or biological processes, called “sinks,” that tend to remove CO₂ from the atmosphere. Significant natural sinks include terrestrial vegetation, which takes up CO₂ during the process of photosynthesis.