The scientific principle behind biomass is the carbon cycle. When they grow, plants absorb carbon dioxide – one carbon and two oxygen atoms (CO2 ). The carbon (C) builds tissues and feeds the plant while the oxygen (O2 ) is released. When plant material is logged and burned, or rots, the carbon recombines with oxygen. The resulting CO2 is released back into the atmosphere. This is roughly three times heavier than carbon, leading to some confusion between tonnes of carbon versus tonnes of CO2 .