Brazilian ethanol expansion subject to limitations

摘要

question the conclusion of Jaiswal et al.1 that ethanol production in Brazil could displace between 3.63 and 12.77 Mbod"1 (million barrels of oil per day) by 2045. Although their study brings novelty, their claim is based on assumptions that overstatethe potential of ethanol.First, the notion that ethanol directly substitutes crude oil is simplistic. Although ethanol production may reach the levels expressed in Mbo, this would not represent direct crude oil substitutability. Ethanol would only displace gasoline in the Otto cycle internal combustion engines found in light-duty vehicles, but not other important oil co-products, such as diesel or kerosene. Moreover, the flexibility needed to alter the output of oil refineries away from gasoline is limited2 4. This flexibilityis higher for complex refineries, especially those equipped with large, severe hydrocracking units, but these are not common worldwide5. In addition, the long-term ethanol market could be challenged by a possible transition to electric vehicles, higher public transportation use and outright reductions in passenger-kilometre demand, given demographic and behaviour transitions6". Importantly, the authors use the high CO_2 concentrations resulting from representative concentration pathway (RCP) 8.5, without noting that, under this scenario, there is no interest in substituting ethanol for crude oil. The RCP 8.5 scenario has no climate mitigation, burns coal for power generation and uses oil in transportation because the costs of renewables do not improve9, meaning second-generation ethanol probably remains uncompetitive. Only an integrated assessment coupled with life-cycle analyses101' could properly assess the global competition between current and future energy and land-use alternatives and the resulting impacts on GHG emissions.