## 3 GHG Emissions and Production Costs of Cellulosic Ethanol  
Cellulosic ethanol from feedstocks such as agricultural residues and energy crops is generally considered to be environmentally sustainable providing higher reduction of GHG emissions and zero or low indirect emissions from land use change compared to conventional (or first generation) ethanol production from food and feed crops. Focusing on the framework after 2020, the RED recast [4] specifies that biofuels must meet a 65% greenhouse gas reduction threshold, compared to fossil fuels, in installations starting operation from 1 January 2021. The methodology to calculate 'life-cycle' GHG emissions is set by the Directive in Anne V part C [4]. GHG emissions should be calculated by taking into account all emissions associated to all steps of the production and use of biofuels, from cultivation of raw materials, to processing into biofuels, and transport and distribution of all products. Emissions from carbon stock changes caused by direct land-use change, if they occurred, should also be taken into account. The total GHG emissions are referred to as 'direct emissions'. The Directive includes a list of default GHG emission values for the main biofuels that economic operators can use only if biofuels are produced without direct land use change. The default value associated to cellulosic ethanol from wheat straw is 16 gCO2 eq/MJ [4] that, compared to the fossil fuel comparator, results in 83% GHG emission reduction. A similar value can be assumed for perennial grass (such as miscanthus and switchgrass) ethanol [29]. However, those values do not include accounting of GHG emissions associated with changes in the carbon stock of land resulting from indirect land use change (ILUC) and other indirect effects. The ILUC issue refers to global market-mediated agricultural area expansion in response to increased biofuel demand. If crops grown on existing arable land are used to make biofuels and are diverted from food and feed production, then the gap in the food supply will be partly filled by the expansion of cropland, because of the necessity to replace the food production. This is referred to as indirect land use change [30]. Economic models are typically used to estimate global land use change consequences due to an increased biofuel demand (more details on how the economic models work and on alternative approaches to estimate ILUC can be found in [30]). ILUC has been estimated by numerous studies in the literature and in regulatory analyses; results show that ILUC emissions can be significant for food-based biofuels [3; 31; 32; 33; 34]. Nevertheless, non-food feedstocks may also have a land use change impact as well as other indirect emissions as a result of the displacement with existing uses [29; 31]. The emissions from land use change calculated by the GLOBIOM (Global Biosphere Management Model) [31] associated to the increase in the demand of cereal straw based ethanol in the EU corresponds to 16 g CO2 eq/MJ of ethanol (assuming 20 years of amortization) in the case of unsustainable straw removal and 0 g CO2 eq/MJ when straw removal is no more than 33-50% of the total straw biomass (considered as the sustainable straw removal in the study [31]). These emissions result from the conversion of land for new cropland for extra cereals production and from the soil organic carbon impact of removing crop residues in unsustainable management [31]. For energy crops/perennial grasses, land use change emissions depends on which type of land is used for their production (existing agricultural land, unused land such as abandoned agricultural land,or high-carbon stock land such as forests) which will in turn be determined by what is more profitable for farmers to do compared to growing other crops or leaving the land uncultivated [35].