What is CO₂ and where does it come from?

Carbon dioxide (CO₂) is a colourless and odourless gas that is a natural component of the air and part of the global carbon cycle. It plays an important role in photosynthesis, in which plants convert CO₂ into oxygen. At the same time, CO₂ is a significant greenhouse gas that contributes to global warming and climate change. Its concentration is influenced by natural processes and human activities such as the burning of fossil fuels. Monitoring and controlling CO₂ emissions are therefore central to environmental protection and climate policy.

What is CO2? - Simply explained

Carbon dioxide (CO2) is an essential component of our atmosphere and is non-toxic, colourless and odourless in gaseous form under natural conditions. The role of CO2 in our climate is crucial: it absorbs some of the heat radiated from the earth and reflects it back to the earth's surface. This natural greenhouse effect regulates the climate on our planet and creates the conditions in which flora and fauna can thrive.

Formation and storage of CO₂ in the natural carbon cycle

CO2 is produced as a natural by-product of cellular respiration in numerous living organisms, the decay of dead organisms and the combustion of organic materials such as wood, coal and gas, or even from natural sources of CO2 (e.g. underwater volcanoes and hydrothermal vents). CO2 sinks are essential to close the natural carbon cycle. In nature, CO2 is broken down by plants through photosynthesis or physically dissolved and stored by bodies of water such as seas and oceans.

The human impact on the climate

Since the beginning of industrialisation (early 19th century), primarily through the burning of coal, oil and natural gas as well as the clearing of forests and draining of wetlands, humans have left behind a considerable carbon footprint. Natural carbon sinks are not sufficient to compensate for anthropogenic CO₂ emissions. The increased greenhouse effect due to human activities, also known as the anthropogenic greenhouse effect, is causing the Earth to warm and has a negative impact on our ecosystem. These include a general increase in temperature, the melting of snow and ice, changes in the acidity of water and the extinction of flora and fauna.


CO2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today's Earth System Models (sciencedirectassets.com)
How much carbon dioxide does the Earth naturally absorb? | MIT Climate Portal


You can find further exciting information on the subject of climate change and climate protection in our climate booklet

How does CO contribute to climate change?

Through the decomposition of organic matter, CO₂ is released into the atmosphere as part of this natural process. At the same time, photosynthesis helps to significantly reduce atmospheric CO₂ . The solubility of CO₂ in water depends on the temperature, so the oceans both produce and reduce CO₂. 

Anthropogenic (man-made) carbon dioxide sources primarily relate to the combustion processes of fossil fuels. CO₂ is an inert end product that accumulates in the atmosphere and is in constant exchange with the biosphere and the oceans. Carbon dioxide reacts with water to form carbonic acid or hydrogen carbonate, which leads to a change in the pH value, i.e. the acidity of the water. Other anthropogenic CO₂ sources that intensify the greenhouse effect include changes to land usage, e.g. the clearing of forests or draining of wetlands such as moors

IPCC 2021 Synthesis Report




You can find further exciting information on the subject of climate change and climate protection in our climate booklet

Calculate your emissions, reduce your carbon footprint and support effective climate protection projects

Caculate now


Stay informed!