Deforestation is the cutting down of trees and is occurring more frequently with each passing year. Without the trees, there is an increase in CO2 in the atmosphere because trees absorb CO2 during photosynthesis. As more carbon dioxide fills the air, the earth becomes warmer. Also, with the loss of trees, species that rely on forests could go extinct. With species going extinct, a chain reaction could start and lead to food shortage, which could lead to humans possibly going extinct.