Carbon dioxide is a colorless, odorless gas made of one carbon atom bonded to two oxygen atoms. Scientists write it as CO₂. Every time you breathe out, you release carbon dioxide that your body created by burning food for energy. Plants do the opposite: they absorb carbon dioxide from the air and use sunlight to turn it into food through a process called photosynthesis, releasing oxygen that we breathe in.

Carbon dioxide plays a crucial role in Earth's climate. It acts like a blanket in the atmosphere, trapping heat and keeping our planet warm enough for life. Without any carbon dioxide, Earth would be frozen. But too much creates problems: when we burn coal, oil, and gas, we release extra carbon dioxide that had been locked underground for millions of years. This extra CO₂ thickens the atmosphere's heat-trapping blanket, causing global temperatures to rise.

You encounter carbon dioxide in everyday life: the bubbles in soda and sparkling water are CO₂ dissolved in liquid. Dry ice, used for special effects and keeping things frozen, is carbon dioxide in solid form. When you blow into a straw in limewater during a science experiment and the liquid turns cloudy, that's the carbon dioxide from your breath reacting with chemicals in the water.