Deforestation is the purposeful clearing of forested land. Forests influence the water cycle through a process called transpiration. Trees absorb water through their roots which is later released as water vapor from their leaves. This water vapor accumulates into clouds until it falls down again as rain, snow, or hail. Trees also absorb carbon dioxide from the atmosphere reducing global warming Global warming occurs when carbon dioxide (CO2) and other air pollutants collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth's surface. Normally this radiation would escape into space, but these pollutants, which can last for years to centuries in the atmosphere, trap the heat and cause the planet to get hotter.