Greenhouse Gas Benefits for Biofuels Depend on a Carbon Credit for Plant Growth Producing Total GHGs & Feedstock Tailpipe Fermen % Increase for Credit for Total GHGs & Source of (crude oil Emis- t-ation Biofuel Without Plant % Savings for fuel* or crop) Refining sions emissions Plant Credit Growth Biofuel Gasoline +4.5 +8 +73.3 - 85.8 - 85.8 EU +61.2 Ethanol +40 +21.2 +71.4 +35.7 168.3 107.1 (+96%) (-29%) Greenhouse gas emissions and sinks (CO2 eqv.) per mega joule of fuel (specific numbers from EU JRC) Effect of switching from gasoline to biofuels grown on otherwise unproductive land – Reduced atmospheric CO2 through increased plant growth emission emission Unproductive 2 2 land New crop growth CO CO Car, gasoline Car, ethanol uptake 2 Gasoline Use Ethanol Use CO 2 Figure 2 - Direct effect of switching from gasoline to biofuels that use existing crops – No change in emissions emission emission 2 2 Crop growth Crop growth CO CO Car, gasoline uptake uptake 2 Car, ethanol Gasoline Use 2 CO CO Ethanol Use 3 Potential market-mediated sources of reduced or additional emissions Crop growth on emission existing cropland 2 emission with price-induced CO . 2 yield gain em CO emission emission 2 2 2 Crop growth CO CO CO Conversion to cropland Car, gasoline Livestock & human Reduced respiration, methane Car, ethanol livestock and wastes uptake & human 2 uptake respiration and 2 CO wastes uptake 2 CO CO Gasoline Use Ethanol Use (vertical arrows indicate carbon uptake and emissions; italics indicates uptake or emission change due to biofuel) ) Benefit v. Cost of Using Land for Ethanol Typical estimates of US High Yield Cellulosic Allowing “Surplus” Carbon cost of corn ethanol savings ethanol saving with Land to Regrow Forest converting existing without land use cost no land use cost and or Convert Tropical forest (1140 liters/hectare no net production Savannah after crediting by- emissions (17 t/ha & products) 100 gallons/t) ~1 ~3 >3 5.5 to ton tons of carbon tons of carbon >10 of carbon per per hectare per per tons of hectare/year year hectare/year carbon per = 34 g CO /MJ = 86 gCO /MJ 2 = 86 g CO2/MJ 2 hectare per year =158 to 287 gCO2/MJ 5 Solar conversion efficiencies Iowa corn Ethanol , 0.125% Most optimistic location future US switchgrass (DOE) (24 tDM/ha and 100 gallons/tonne) 0.35% Brazilian sugarcane ethanol , 0.2% PV – 16% gross; 11% net .