Carbon dioxide or CO2 is a colorless gas with a density about 53% higher than that of dry air. Plants such as green leaves use energy from sunlight though photosynthesis to chemically combine carbon dioxide drawn in from the air with water and nutrients tapped from the ground to produce sugars, which are the main source of food and food gives us energy. Trees which have green leaves filter the air. They make CO2 into oxygen for us to breathe. If we cut down trees there will be more carbon dioxide in the air which is bad for us. Most trees are in rainforests but nowadays some people are cutting down trees. A way we can fix the problem is by planting more trees. Carbon dioxide can be harmful and helpful its just how we treat the Earth.