Electric light-duty vehicles have decarbonization potential but may not reduce other environmental problems

This section first analyzes the environmental impact of the vehicle cycle (i.e., global warming potential and respiratory effects). Subsequently, we present the vehicle lifecycle global warming potential results under the current, baseline STEPS, and APS scenarios. We then show the results for one localized impact—respiratory effects—under these scenarios. Finally, we conduct a detailed analysis of the respiratory effects, splitting them into tailpipe and non-tailpipe emissions.

Figure 2 shows a breakdown of the impacts of the vehicle cycle: Fig. 2a illustrates the global warming potential (GWP), and Fig. 2b depicts the respiratory effects (RE). The vehicle cycle includes everything except the fuel cycle operation of the vehicle over its lifetime30. Each light-duty vehicle has a different environmental impact. BEVs have the highest global warming potential and respiratory effects. Their values are noticeably higher than those of PHEVs (44% and 33% more for GWP and RE, respectively), which in turn are greater than HEVs (18% and 13% more for GWP and RE, respectively). HEVs and ICEVs have similar impacts (below 5% variance for both GWP and RE). BEVs’ environmental footprint is attributed mainly to the batteries, contributing 50% of the global warming potential and 45% of the respiratory effects. In contrast, the smaller-capacity battery pack of PHEVs contributes to 17% and 15% of global warming potential and respiratory effects, respectively. Apart from battery-related effects, the environmental impacts of all other parts remain relatively consistent across all light-duty vehicles, except BEVs, which have considerably lower maintenance requirements compared to their internal combustion engine counterparts, primarily due to the absence of engine oil replacements (see Supplementary Table S2). In summary, the vehicle cycle of PHEVs and BEVs entails a considerable environmental impact, primarily due to batteries having emissions-intensive processes involved in the extracting and processing of materials, manufacturing, and assembly31. Our objective in the following sections is to explore under what circumstances BEVs offset the higher environmental impact associated with their vehicle cycle and potentially outperform ICEVs, HEVs, and PHEVs across their entire lifecycle. This includes an in-depth comparison of the lifetime environmental impact of these vehicles under different use cases.

We identify two factors that introduce substantial variability in the results across these four regions: BEV electricity consumption and PHEV electric driving share (see Methods). This main text focuses on analyzing one factor: PHEV electric driving share. For a detailed analysis of the other factor, BEV electricity consumption, refer to Supplementary Note 8.

We combine the vehicle cycle impacts (Fig. 2) with the fuel cycle impacts to calculate the full lifecycle impacts of each light-duty vehicle. Then, we compare the full lifecycle environmental impacts of these vehicles using two important parameters: the first is the lifetime vehicle driving distance (km), and the second is the PHEV electric driving share (%), i.e., the percentage of driving done by PHEV that is powered by the battery versus the gasoline engine. In Fig. 3, we map these two parameters to create a landscape split into different colored areas to denote which vehicle (pink for ICEV, blue for HEV, yellow for PHEV, and green for BEV) has the lowest global warming potential for the combination of these two parameters. This landscape is repeated for different regions: global (Fig. 3a), Norway (Fig. 3b), the US (Fig. 3c), and China (Fig. 3d). The electricity grid mixes for these four regions are based on the current scenarios. For a description of how this plot was developed, see the Methods Section.

Firstly, it is worth highlighting that across all four regions, ICEVs capture a noticeably small fragment of the landscape, with their share varying by region but consistently below 1700—lifetime vehicle kilometers. For all other vehicles, substantial disparities exist among these four regions.

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For the global region (Fig. 3a, average grid emissions of 0.72 kg CO2-eq kWh−1), BEVs have the lowest global warming potential for only a small portion of the landscape, above 270,000 km and below a PHEV electric driving share of 26–31%. The rest of the landscape is almost evenly split between PHEV and HEV, with HEV dominating for low lifetime vehicle driving distance and PHEV electric driving share (toward the bottom left of the landscape), and PHEV dominant elsewhere.

Moving to a relatively cleaner grid, as represented by the US (Fig. 3c, average emissions of 0.55 kg CO2-eq kWh−1), we observe that BEVs capture more of the landscape, winning out over HEVs above a lifetime driving distance of 82,000 km and over PHEVs when the PHEV driving share is between 27 and 70%, depending on the lifetime driving distance.

In Norway where the grid is the cleanest among all four regions (Fig. 3b, average emissions of 0.02 kg CO2-eq kWh−1), BEVs clearly dominate the landscape, beating out HEVs over 26,000 lifetime vehicle kilometers and PHEVs even up to a PHEV electric driving share of 94% (again depending on the lifetime vehicle kilometers). This trend suggests that as the proportion of low-carbon energy in the electricity grid increases, the environmental advantages of BEVs increase as evidenced by the expansion of BEVs’ colored area towards lower driving distance values in the plot. This shift indicates that BEVs, powered with a cleaner energy mix, offset battery production’s environmental impact at lower driving distance compared to using higher-emission electricity grids for charging, i.e., BEVs’ ‘clean tech’ status is a function of both vehicle and grid together.

In China’s dirty grid (Fig. 3d, average grid emissions of 1.04 kg CO2-eq kWh−1), HEVs strongly dominate. Both BEVs and PHEVs fail to offset the extra environmental burden of battery production. Contrary to expectations, driving battery-powered kilometers results in a higher global warming potential than driving gasoline-powered kilometers. This is due to the high greenhouse gas emissions associated with electricity production from the Chinese grid. This cumulative effect escalates with increasing driving distance, resulting in the total impact of BEVs and PHEVs consistently exceeding that of HEVs (the sum of the vehicle and fuel cycle emissions). This issue is further discussed in Supplementary Note 6 and Note 7.

In this section, we present the most likely future pathway results for the global warming potential of PHEVs and BEVs (i.e., baseline STEPS scenarios), analyzed together with ICEVs and HEVs, complemented by results from the APS scenarios.

Figure 4 shows the global warming potential results under the baseline STEPS scenarios in the US (Fig. 4a) and China (Fig. 4b), and under the APS scenarios in the US (Fig. 4c) and China (Fig. 4d). In the US, BEVs dominate the landscape, beating out HEVs over 36,200 lifetime vehicle kilometers and PHEVs up to a PHEV electric driving share of 89% under the baseline STEPS scenario (0.24 kg CO2-eq kWh−1). Similarly, BEVs beat out HEVs over 32,600-lifetime vehicle kilometers and PHEVs up to a PHEV electric driving share of 90% under the APS scenario (0.18 kg CO2-eq kWh−1).

In contrast, in China, BEVs outperform HEVs at longer lifetime vehicle kilometers and PHEVs up to a lower PHEV electric driving share. Specifically, BEVs outperform HEVs at 90,600 lifetime vehicle kilometers and PHEVs up to a PHEV electric driving share of 67% under the baseline STEPS scenario (0.58 kg CO2-eq kWh−1), and at 70,500-lifetime vehicle kilometers and a PHEV electric driving share of up to 74% under the APS scenario (0.52 kg CO2-eq kWh−1). In both countries, the greater landscape expansion of BEVs in the APS scenarios compared to the baseline STEPS scenarios is attributed to a further decline in the average carbon emissions from the grid mix. We also provide a detailed analysis of vehicles with a fixed lifetime distance of 320,000 km (Supplementary Fig. S4).

Also shown in Fig. 3 and Fig. 4 are the average values for the PHEV electric driving share in the different regions (dashed horizontal lines) and the average lifetime vehicle driving distance in the US (dashed vertical lines). Taking the US as an example (Fig. 4a and Fig. 4c), for the average lifetime driving distance of 241,400 km (vertical dash line) and the average PHEV electric driving share in the US of 54%32, BEVs have the lowest global warming potential (see the intersection of vertical and horizontal dashed lines in the figure). For the ‘average’ driver, BEV stands out as the lowest-carbon emission option. Consumers should evaluate if their personal use aligns with these average conditions, such as access to workplace charging stations. Policymakers could explore options to change the average scenarios, like increasing public charging station accessibility. These topics are further elaborated in the Discussion Section.

Turning to a localized impact, Fig. 5 shows which vehicle type has the lowest respiratory effects under current scenarios. In the four regions examined, ICEVs have the lowest respiratory effects up to a specific vehicle distance threshold (ranging from 9200 to 10,000 km). Beyond these thresholds, HEVs demonstrate the lowest respiratory effects in the globe, the US, and China. This is because electricity production in these regions has a higher respiratory effect than gasoline use (i.e., the well-to-tank process). The gasoline use emissions include gasoline combustion during vehicle operation and upstream emissions required for gasoline production33. Therefore, despite the widespread promotion of BEVs, HEVs offer better environmental benefits in terms of respiratory effects. However, Norway is an exception, resembling the results in Fig. 3b due to the country’s distinctive electricity grid, which primarily relies on hydropower with minimal respiratory effects.

Similar to the global warming potential analysis, we examine the respiratory effects of light-duty vehicles under the baseline STEPS and APS scenarios in the US and China. However, the pattern of results in both scenarios remains unchanged from the current scenarios (see Supplementary Fig. S11), with HEVs continuing to strongly dominate.

Given the localized nature of respiratory effects, which differ from the global impact of global warming potential, we split respiratory effects between the tailpipe and non-tailpipe emissions, which occur in different locations. This approach allows us to better understand the environmental and health implications at a local level.

We fix the vehicle lifetime distance at 320,000 km and break down respiratory effects impact into the tailpipe and non-tailpipe emission categories. The non-tailpipe emissions include the vehicle cycle, the well-to-tank process (which includes crude oil extraction, refining, storage, transportation, etc.)34, and electricity generation. We consider both the baseline STEPS and APS scenarios for the grid mix in the US and China.

As shown in Fig. 6, respiratory effects for BEVs and PHEVs under APS scenarios are lower than under baseline STEPS scenarios in both countries due to reduced respiratory effects per kWh of electricity. However, the total respiratory effects from BEVs and PHEVs remain higher than those of HEVs (10.3 kg PM2.5 eq in the US and 10.1 kg PM2.5 eq in China). Surprisingly, the tailpipe respiratory effects constitute a small portion (less than 4%) of the total. This pattern is also observed for other impact categories except for global warming potential (See Supplementary Note 4). Notably, the primary sources of total respiratory effects are non-tailpipe emissions, mainly from electricity generation (for electric driving) and well-to-tank processes (for gasoline driving). Moreover, we note that PHEVs, when relying more on electricity, can increase total respiratory effects compared to gasoline. For example, under the US baseline STEPS scenario, as the PHEV electric driving share increases from 0% to 100%, total respiratory effects also rise from 10.8 to 18.1 kg PM2.5 eq.