Carbon diox­ide is a color­less gas consist­ing of the elements carbon and oxygen, which plays an impor­tant role in climate change. In German-speak­ing coun­tries, carbonic acid is often mistak­enly referred to collo­qui­ally as ‘carbon diox­ide’. Carbon diox­ide is one of the most impor­tant green­house gases, because it absorbs some of the heat that the Earth emits into space and radi­ates it back to Earth. This creates a temper­ate climate on Earth. However, human activ­i­ties have greatly increased the CO₂ concen­tra­tion in the atmos­phere, which contributes to global warming.

Carbon diox­ide in low concen­tra­tions is a natural compo­nent of the air we breathe and is produced, among other things, during the combus­tion of fossil fuels, such as natural gas, crude oil and coal. The gas is widely used in indus­try, for exam­ple in solid form as dry ice, as a fertil­izer in green­houses, as a solvent or as an addi­tive in soft drinks.