Carbon dioxide is emitted from both natural and human sources. Natural sources of carbon dioxide include:
- Decomposition of organic matter, such as plants and animals
- Respiration by living organisms, including animals and plants
- Forest fires
- Volcanic eruptions
- Ocean release
Human activities also contribute to carbon dioxide emissions, including:
- Combustion of fossil fuels, such as coal, oil, and natural gas, for transportation, electricity, and heating
- Cement production
- Deforestation
- Organic waste sent to landfills
- Wastewater treatment plants
- Anaerobic digestion at biogas facilities
- Fluorinated gases used in air conditioning and refrigeration systems
It is important to note that while natural sources of carbon dioxide exist, human sources have upset the natural balance that existed for many thousands of years before the influence of humans.