After rain falls on a forest, mist rises and new rain clouds form. When forests are cut down, this cycle is disrupted, and the area eventually grows drier, causing a change in the local climate. If huge area of trees are cut down, the carbon dioxide they would have used builds up in the atmosphere and contributes to the greenhouse effect. And without trees to hold the soil and absorb water, rain washes topsoil away, a process called soil erosion.