A reasonable assumption is that the same amount of
carbon released by energy utilization of biomass is sequestered
in new biomass growth. Thus, biomass systems have no net
impact on global warming, which is a considerable benefit
compared with fossil fuels. This picture is, however, not
completely true because in most cases fossil fuels are needed
to produce, harvest, transport and convert biomass to usable
energy. Calculations on forestry systems done by Enger (1983)
indicate that the input of fossil energy is less than 5% of the
energy content in the wood. For energy crops in agriculture,
French studies of biofuel systems cited in Ruiz-Altisent et al.
(1994) indicate a reduction of carbon emissions, of 70%
relative to standard gasoline.