carbon dioxide

Colourless, odourless gas, slightly soluble in water, and denser than air. It is formed by the complete oxidation of carbon. Carbon dioxide is produced by living things during the processes of respiration and the decomposition of organic matter, and it is used up during photosynthesis. It therefore plays a vital role in the carbon cycle.

Solid carbon dioxide is called dry ice, as it changes directly from a solid to a gas (sublimes) on warming. It is used as a coolant in its solid form and in the chemical industry.

Its increasing quantity in the atmosphere contributes to the greenhouse effect and global warming. Britain has 1% of the world's population, yet it produces 3% of CO₂ emissions; the USA has 5% of the world's population and produces 25% of CO₂ emissions. Despite growing awareness of the problem, carbon dioxide levels continue to rise worldwide.