Too much carbon dioxide (CO2) in the atmosphere is mostly caused by two things: burning fossil fuels and the loss of trees. Urban trees help to keep urban areas cooler, they hold soil in place, they make urban areas prettier, and they help to keep urban areas quieter. They also absorb CO2 from cars, buses, and the many engines that are used in urban areas. When people plant and maintain urban trees, they usually use machines with engines which emit CO2. When a tree is cared for using machines wi Topics: Active Forest Management, Carbon, Pollution, Carbon Cycle, Carbon Dioxide, Cost-Benefits Analysis, Fossil Fuels, Photosynthesis.