CO₂, or carbon dioxide, is a colourless and odourless gas which is produced when carbon is burned and combines with oxygen. Carbon dioxide is also produced in the metabolism of all living creatures where it is released via cell respiration.

With a concentration of approximately 0.04%, CO₂ is a natural component of the air and does not endanger our health in any way. Only in concentrations of 5% and more, as encountered in poorly ventilated wine cellars, for instance, it may lead to headaches, dizziness or unconsciousness.

Fossil fuels can also be regarded as natural CO₂ reservoirs as long as they are not burned for energy production. The gas emissions from these natural CO₂ reservoirs regulate the CO₂ balance in the atmosphere. The problems come when CO₂ is released to the atmosphere during the combustion of fossil fuels, intensifying the greenhouse effect.
Carbon dioxide - structure (click to enlarge)

Experts reckon that a rise in CO₂ concentrations will possibly lead to a marked warming of the earth's atmosphere and a shift in climate zones in the future. That is why CO₂ emission reduction is among the biggest challenges we have to master today and in the future.

CO₂ concentrations (volume percent) in the air and their effects on humans

• 0,04 percent: Usual air concentration
• 4 percent: Exhaled air
• 5 percent: Headaches and dizzines
• 8 percent: Unconsciousness

A concentration of more than 5 percent can only be reached under special conditions, e.g. in poorly ventilated wine cellars, fodder silos, wells or cesspools.As the density of CO₂ is 1.5 times the density of air, CO₂ accumulates in deep spots, e.g. in depressions. That is why depressions are avoided during the planning of RWE Dea's climate protection pipeline so that in the unlikely event of a CO₂ leak, the CO₂ does not accumulate but whirls in the air.