The global transition to electric vehicles (EVs) is widely seen as crucial for mitigating climate change. The International Energy Agency (IEA) reported that EVs contributed to a net reduction of 40 million tonnes of CO₂e in 2021. Despite varying assessments due to differing methodologies, the long-term climate benefits of EVs compared to ICEVs, particularly with decarbonizing electricity generation, are generally accepted. This has led to a rapid expansion of the EV market globally, with ambitious electrification targets set by many countries, including a 50% electric vehicle target for new sales in the US by 2030 and a ban on new gasoline and diesel vehicles in the EU by 2035. China, a global leader in the EV market, has also implemented significant policies to support EV deployment as a key element of its carbon neutrality goals. While the climate benefits of BEVs are acknowledged, a critical factor often overlooked is the time lag before these benefits materialize. The production of BEVs, especially battery manufacturing, typically generates more greenhouse gas emissions than ICEV production. This "GHG debt" needs to be repaid through the operational phase of the vehicle before net climate benefits are realized. Most studies comparing BEV and ICEV life-cycle emissions tend to distribute emissions evenly over the vehicle's lifespan, neglecting this temporal aspect. Only a few studies have focused on the delayed climate benefits of BEVs, often examining specific models rather than providing a national-level perspective. This study aims to address this gap by analyzing a large dataset of Chinese vehicle sales to quantify the delay in climate mitigation benefits associated with BEVs in China, informing effective decarbonization policies.

Existing literature supports the long-term climate benefits of electric vehicles compared to internal combustion engine vehicles, especially with the continued decarbonization of electricity grids. However, many studies simplify the life-cycle assessment (LCA) by evenly distributing emissions over the vehicle's lifespan, neglecting the significant upfront emissions associated with BEV manufacturing, particularly battery production. This leads to an incomplete picture of the true climate impact, underestimating the time it takes for a BEV to offset its initial carbon debt. Some studies have examined this 'greenhouse gas break-even time' (GBET) for specific vehicle models or in specific geographic regions but lack the breadth of a national-scale analysis using large datasets. The existing research highlights the need for a more comprehensive understanding of the temporal dynamics of BEV climate benefits to effectively guide policymaking and inform strategies for deep decarbonization in the transportation sector. The lack of a comprehensive understanding of the time delay in realizing climate benefits from BEVs makes it difficult for policy makers to accurately evaluate the effectiveness of their efforts and to design appropriate policies to achieve climate goals.

This study quantifies the greenhouse gas break-even time (GBET) of BEVs in China using a large-scale dataset encompassing almost all BEVs (nearly 1.5 million) and 82% of ICEVs (145.9 million) in the light-duty passenger vehicle category produced and sold between 2012 and 2018. The data were sourced from China's Compulsory Traffic Accident Liability Insurance (CTALI) database, supplemented by vehicle model specifications from the Ministry of Industry and Information Technology (MIIT). The GBET estimation relies on a life cycle assessment (LCA) using the China Automotive Life Cycle Assessment Model (CALCM), which considers both vehicle-cycle and fuel-cycle emissions. The vehicle-cycle emissions encompass raw material acquisition, material processing, manufacturing, vehicle production, and maintenance. The fuel-cycle emissions consider "well-to-wheel" emissions for ICEVs (crude oil extraction, refining, fuel combustion) and "well-to-wheel" emissions for BEVs (electricity production, transmission, and use). Each BEV was paired with a representative ICEV of the same vintage, transport mode (car, SUV, MPV), and size class (A00, A0, A, B, C) for GBET calculation. The GBET was calculated by comparing the vehicle-cycle GHG emissions difference between the BEV and its ICEV counterpart (representing the initial GHG debt) with the cumulative difference in yearly fuel-cycle emissions over the vehicle's lifespan. This approach accounts for the time it takes for the BEV to offset its initial carbon debt. Sensitivity and uncertainty analyses were conducted to assess the impact of various parameters and comparison benchmarks on GBET estimations. The sensitivity analysis used a one-variable-at-a-time perturbation method to identify the most influential factors. Uncertainty analysis utilized a combination of the range approach and orthogonal experimental design (OED) to explore the effects of variations in key parameters on GBET, including curb weight, GHG emission factors of vehicle materials, battery capacity, GHG emission factors of battery materials, annual vehicle kilometers traveled (VKT), and GHG emission factors of power grids. The study also considered variations in ICEV benchmarks, comparing BEVs with average ICEVs, high-emission ICEVs, and low-emission ICEVs within the same or adjacent size classes to analyze the impact of these choices on GBET estimates. Provincial-level data, including annual VKT and GHG emission intensities of power grids, were used to explore the regional heterogeneity of GBET.

The study confirms the existence of a significant GHG debt for BEVs in China. The average GHG emissions of BEV production are approximately 1.4 times higher than those of ICEV production. The average GBET for BEVs in China is 4.5 years, ranging from zero to over 11 years. The GBET distribution is skewed, with approximately 70.4% of vehicles paying off their GHG debt within one standard deviation (2.1–6.9 years). Around one-fifth of BEVs sold before 2016 failed to meet the five-year battery warranty GBET requirement, and 8% of those sold between 2016 and 2018 did not meet the extended eight-year warranty requirement. The GBET varies significantly across vehicle classes and sizes. Larger vehicles generally have longer GBETs due to higher battery capacity and weight, increasing the initial GHG debt, although this effect is somewhat counteracted by larger reductions in fuel-cycle emissions for larger, higher-emission ICEV counterparts. Regional heterogeneity in GBET is substantial, with significant differences across provinces primarily driven by variations in electricity grid GHG emission intensity, vehicle size/type, and annual VKT. Northeastern provinces had considerably longer GBETs (6.9–7.9 years) than southwestern provinces (2–6 years shorter), attributable to higher GHG emission intensities of their power grids and lower annual VKT. Tibet, despite having the lowest electricity grid emission intensity, exhibited a very long GBET due to exceptionally low annual VKT. Sensitivity analysis revealed that GBET is more sensitive to vehicle-cycle factors (curb weight, battery capacity, GHG emission factors of materials) than fuel-cycle factors (annual VKT, GHG emission factors of power grids), contrasting with some previous LCA studies. Uncertainty analysis, considering a range of input parameters and different ICEV benchmarks, showed that the national average GBET could range from -1.9 years to 6.5 years, depending on the assumptions. Using low-emission ICEVs as benchmarks increased the GBET substantially, while high-emission ICEVs led to considerable decreases.

The findings highlight the importance of considering the temporal dimension of climate mitigation benefits when evaluating BEVs. The substantial GHG debt associated with BEV production underscores the need for policies that extend beyond simply increasing BEV sales. The development of new indicators, such as the percentage of BEVs that have reached GBET (P-GBET), can provide a more nuanced assessment of the actual climate benefits of BEV deployment compared to the commonly used BEV penetration rate. Current policies often focus on incentivizing BEV purchases, but these incentives may not be effective in achieving substantial climate benefits if the vehicles do not reach their GBET. The GBET can also inform the setting of technical standards, such as battery warranty periods, to ensure that vehicles provide net climate benefits within a reasonable timeframe. The results also suggest a need for policies that promote increased vehicle utilization to shorten GBET, such as promoting vehicle sharing or prioritizing BEVs as taxis. Location of BEV production relative to renewable energy sources is another critical consideration. Aligning BEV production sites with regions having clean power sources can significantly reduce the initial GHG debt and improve the overall climate performance. While there may be trade-offs between life-cycle emissions reductions and faster GBET, synergies are possible through technological advancements such as vehicle lightweighting, material recycling, battery recycling and reuse, and improved electricity grid decarbonization.

This study demonstrates that the climate benefits of BEVs in China are significantly delayed due to their carbon-intensive production process. The GBET provides a crucial metric for evaluating the true climate impact of BEV deployment. Policies should move beyond simply increasing BEV sales to focus on strategies that enhance effective BEV substitution of ICEVs, promote increased vehicle utilization, and align BEV production with renewable energy sources. Further research could explore the impact of consumer behavior on effective substitution mileage and the use of more sophisticated LCA methods that incorporate the time-varying nature of electricity grid emissions and battery degradation.

Several limitations should be considered. The study assumes a constant effective substitution mileage for BEVs, neglecting rebound and spillover effects of BEV adoption. The lack of real-world vehicle-level data on fuel efficiency and real-time GHG emission factors may introduce bias into GBET estimations. The study does not fully account for battery recycling, degradation, or the impact of older, less efficient vehicles remaining in the fleet. The use of average annual power grid emission factors may also underestimate GBET due to daily and seasonal variations.