Carbon dioxide (CO2) is produced from both natural and human-related sources: Natural causes:

• Respiration: Animals and humans release CO2 when they breathe out as a byproduct of cellular respiration, where glucose and oxygen are converted into energy, CO2, and water.
• Decomposition: When plants and animals die, bacteria decompose the organic material, releasing CO2.
• Volcanic eruptions: Volcanoes emit CO2 from the Earth's interior.
• Forest fires: Combustion of biomass releases CO2.
• Weathering of carbonate rocks: CO2 dissolves in rainwater forming carbonic acid, which reacts with rocks releasing CO2 back into the atmosphere.
• Plant decay and ocean processes also contribute to natural CO2 cycling

Human causes:

• Burning fossil fuels: The combustion of coal, oil, and natural gas for energy and transportation releases large amounts of CO2 that were previously stored underground for millions of years.
• Deforestation: Reduces the number of trees that absorb CO2 during photosynthesis, increasing atmospheric CO2 levels.
• Cement production and other industrial processes also emit CO2.
• Human activities have significantly increased atmospheric CO2 since the 1800s, raising levels from about 280 ppm pre-industrial to over 415 ppm today, driving climate change

In summary, carbon dioxide is caused by natural biological, geological, and chemical processes, as well as by human activities primarily related to fossil fuel combustion and land use changes