"Most of the earth's land mass is located in the northern hemisphere, as is most of the earth's vegetation. During autumn and winter, millions of tons of leaves fall fall from deciduous trees and as they decompose, they give off carbon dioxide. The trees themselves no longer process as much carbon dioxide as they are in somewhat of a dormant state. As a consequence, the earth's carbon dioxide levels rise.
Throughout the spring and summer days, leaves grow rapidly and a great deal of carbon dioxide is consumed in the growing of the leaves and subsequent normal respiration processes - so the CO2 level drops."
BTW when did they decide carbon dioxide is pollution?