The data presented in Sect. 4.3 for the four maj or determinants of net greenhouse gas emissions will be used in this section to calculate life cycle emissions for specific biofuels and categories of transport biofuels.

4.4.1 Net Greenhouse Gas Emissions for Specific Biofuels

Example 1: Electricity from Woody Biomass Instead of from Fossil Fuels

Substituting fossil fuels with woody biomass from sustainably managed forests in electricity production will strongly reduce the life cycle greenhouse gas emissions per kWhe, as indicated by Fig. 4.2.

However, when there are changes in C sequestration due to forestry, emissions may deviate in a major way from the values in the last column of Fig. 4.2. Nechodom et al. (2008) have given a far more favourable assessment of electricity generated by burning woody biomass from forest remediation in California, as such remediation is supposed to reduce C losses due to fires, whereas use of woody biomass associ­ated with clear cutting forests will lead to greenhouse gas emissions that are much

larger than those associated with the fossil fuels given in Table 4.1 (Reijnders and Huijbregts 2003). There may also be temporal deviations from the woody biomass value given in Fig. 4.2 when the requirement is that cutting trees should be bal­anced by planting new trees. In this case, there may be a period of up to 20-40 years after harvesting in which forests are net sources of atmospheric carbon, and even longer periods before initial C losses are fully compensated (Reijnders and Huijbregts 2003).