Does the metric matter? Climate change impacts of light-duty vehicle electrification in the US

Vehicle electrification is one of the most promising climate change mitigation strategies for light-duty vehicles (LDVs). But vehicle electrification shifts the greenhouse gas (GHG) emission profiles of conventional LDVs with emissions moving upstream from vehicle use to electricity generation and vehicle production. Electric vehicle (EV) deployment needs to be examined with life cycle assessment (LCA), both at vehicle and fleet levels. Climate change assessments of EVs are usually conducted using global warming potential (GWP), a normalized metric that aggregates GHG emissions. GWP suffers from some limitations as it ignores the emission timing over the product life cycle. In this study, we examine climate change impacts of four vehicle technologies (conventional, hybrid, plug-in hybrid, and battery electric vehicles) in the US at vehicle and fleet levels using four climate change metrics (GWP, dynamic global warming impact, radiative forcing impact and global temperature change impact). One of our key findings is that while the choices of the metric, the analytical time period, and some other key parameters, such as methane leakage rate, may have substantial influences on the results, partial and full electrification remain effective solutions to reduce climate change impacts of the US LDVs. However, the transient effects that exist between GHG emissions, radiative forcing, and global temperature changes imply that climate change impact reductions of vehicle electrification take time to materialize and are overestimated with GWP. It is therefore critical to evaluate large-scale implications of climate change mitigation strategies with multiple metrics to fully capture and assess the expected benefits. We nonetheless found that GWP is a robust metric for climate change mitigation targets of vehicle electrification and remains a good choice for most analysis.