ABSTRACT
An important advantage of biofuels over fossil fuels, apart from their being renewable, is that biofuels in principle can be used without adding any net CO2 to the atmosphere provided that during the growth of the biomass CO2 was removed from the atmosphere by no more than the amount it is later added when the fuel is consumed. In this case, we would describe the biofuel as being carbon-neutral (or perhaps even carbon-negative) over their life cycle. Of course, this assertion assumes that the CO2 emitted during the planting, cultivating, and harvesting the biomass, along with that released when it is converted to a biofuel and finally transported and used are not great enough to alter the balance, which need not be the case. Nevertheless, biofuels generally are considered to come under the heading of renewable energy sources, and in fact comprise about 63% of them.
