Green plants contribute to the filtration of the air of our planet. They provide the ability for us to breathe. Plants take in carbon dioxide and release oxygen. We breathe oxygen and release carbon dioxide. It is a codependent relationship we depend on. Where would the oxygen come from if all the plants, trees and fields of grasses were gone??? Yes some would come from the oceans evaporation, but not enough. Since humankind is stripping the trees from the planet faster than they can grow to replace the demand, what do you think is happening to our atmosphere? Global warming is a direct result of loosing the trees.....period. Can you tell it is a subject near and dear to my heart. It is a sad thing to me that we continue to pave the surface of the earth with cement. It is even sadder that for the most part people do not even think about it.