Climate Impacts of Short-Lived Climate Forcers versus CO₂ from Biodiesel: A Case of the EU on-Road Sector

Biofuels are proposed to play an important role in several mitigation strategies to meet future CO₂ emission targets for the transport sector but remain controversial due to significant uncertainties in net impacts on environment, society, and climate. A switch to biofuels can also affect short-lived climate forcers (SLCFs), which provide significant contributions to the net climate impact of transportation. We quantify the radiative forcing (RF) and global-mean temperature response over time to EU on-road fossil diesel SLCFs and the impact of 20% (B20) and 100% (B100) replacement of fossil diesel by biodiesel. SLCFs are compared to impacts of on-road CO₂ using different approaches from existing literature to account for biodiesel CO₂. Given the best estimates for changes in emissions when replacing fossil diesel with biodiesel, the net positive RF from EU on-road fossil diesel SLCFs of 3.4 mW/m² is reduced by 15% and 80% in B20 and B100, respectively. Over time the warming of SLCFs is likely small compared to biodiesel CO₂ impacts. However, SLCFs may be relatively more important for the total warming than in the fossil fuel case if biodiesel from feedstock with very short rotation periods and low land-use-change impacts replaces a high fraction of fossil diesel

Climate Effects of Emission Standards: The Case for Gasoline and Diesel Cars

Passenger transport affects climate through various mechanisms involving both long-lived and short-lived climate forcers. Because diesel cars generally emit less CO₂ than gasoline cars, CO₂ emission taxes for vehicle registrations and fuels enhance the consumer preference for diesel cars over gasoline cars. However, with the non-CO₂ components, which have been changed and will be changed under the previous and upcoming vehicle emission standards, what does the shift from gasoline to diesel cars mean for the climate mitigation? By using a simple climate model, we demonstrate that, under the earlier emissions standards (EURO 3 and 4), a diesel car causes a larger warming up to a decade after the emissions than a similar gasoline car due to the higher emissions of black carbon and NO_X (enhancing the O₃ production). Beyond a decade, the warming caused by a diesel car becomes, however, weaker because of the lower CO₂ emissions. As the latter emissions standards (EURO 5 and 6) are phased in, the short-term warming due to a diesel car becomes smaller primarily due to the lower black carbon emissions. Thus, although results are subject to restrictive assumptions and uncertainties, the switch from gasoline to diesel cars encouraged by CO₂ taxes does not contradict with the climate mitigation focusing on long-term consequences

Climate Penalty for Shifting Shipping to the Arctic

The changing climate in the Arctic opens new shipping routes. A shift to shorter Arctic transit will, however, incur a climate penalty over the first one and a half centuries. We investigate the net climate effect of diverting a segment of Europe–Asia container traffic from the Suez to an Arctic transit route. We find an initial net warming for the first one-and-a-half centuries, which gradually declines and transitions to net cooling as the effects of CO₂ reductions become dominant, resulting in climate mitigation only in the long term. Thus, the possibilities for shifting shipping to the Arctic confront policymakers with the question of how to weigh a century-scale warming with large uncertainties versus a long-term climate benefit from CO₂ reductions