Greenhouse gases are special gases in the air that trap heat. The most famous one is carbon dioxide, or CO2. We make CO2 when we burn things like gas in cars. Another greenhouse gas is methane. Methane comes from cows and landfills where trash is buried. Water vapor is also a greenhouse gas. It's just water in the air, like the steam you see from a hot cup of tea. These gases act like a blanket, keeping Earth warm.
1. What do greenhouse gases do?
2. Which of these is NOT mentioned as a greenhouse gas?
3. Where does methane come from?
4. How are greenhouse gases described in the text?