Koldioxid, or carbon dioxide (CO2), is a colorless gas that is naturally present in Earth's atmosphere. It is produced by the respiration of animals and plants, as well as through the combustion of fossil fuels like coal, oil, and natural gas. Koldioxid plays a crucial role in the carbon cycle, where it is absorbed by plants during photosynthesis to produce oxygen. In addition to its natural sources, koldioxid is also a byproduct of various industrial processes. It is used in the production of carbonated beverages and as a refrigerant. Elevated levels of koldioxid in the atmosphere contribute to global warming and climate change, making it an important focus for environmental science and policy.