Two processes of natural absorption of carbon dioxide were researched.The first is the decomposition of carbon dioxide by photons of sunlight. Time of decomposition of 1 mg of carbon dioxide equals 17.7 days. In the second process - the absorption of 1 mg of carbon dioxide by plants takes 10.5 days.Experiments were performed with carbon dioxide dissolved in water. The mass of carbon dioxide is 84.5 mg in 0.05 l of water. Chlorophyll was used as a catalyst, a 100 W incandescent lamp with a reflector was used as light. The estimated time to complete the reaction was 227 days. After evaporation of the solution, carbon crystals were obtained. It is concluded that the process of recycling carbon dioxide from the atmosphere by photosynthesis is slow. It is necessary to develop more effective ways to combat the increase of greenhouse carbon dioxide in the Earth's atmosphere.