However, the carbon-negative status of the technology has been questioned by Bruun
(2008), who considered the additional fossil fuel offset that could be obtained if biochar was
used for non-energy purposes. Furthermore, biomass pyrolysis itself did not extract more
energy from a feedstock when compared to another bioenergy use. Bruun (2008) also
pointed out that over longer timescales, an increasing proportion of the carbon initially
sequestered in biochar would be slowly returned to the atmosphere through its slow
degradation back to CO2.