Windows to the Universe original artwork by Randy Russell.
Carbon dioxide (CO2) is a kind of gas. There isn’t that much carbon dioxide in Earth’s atmosphere, but it is still very important. Carbon dioxide is a greenhouse gas. That means it helps trap heat coming from the Sun in our atmosphere through the greenhouse effect. Without carbon dioxide in our air, the Earth would be very cold.
Where does the carbon dioxide in our air come from? When humans and other animals breathe, we take in oxygen and breathe out carbon dioxide. We use the oxygen to get energy from food – this is called respiration.
Burning things also makes lots of carbon dioxide. Natural fires like forest fires make carbon dioxide. Things that humans burn make CO2, too. The smokestacks of factories that burn coal give off carbon dioxide. The engines of cars, trucks, and buses also pump carbon dioxide into the air. They sometimes give off another gas, carbon monoxide, too.
Earth isn’t the only place where carbon dioxide is important. Most of the atmosphere of Venus is CO2. The atmosphere of Mars is also mostly carbon dioxide. If carbon dioxide gets really cold, it can freeze into a solid. This kind of ice is called “dry ice”. The polar ice caps on Mars are partly made of dry ice!
source: windows to the universe