A new study by researchers at the University of Toronto has found that current US policies are insufficient to remain within a sectoral CO₂ emission budget for light-duty vehicles that is consistent with preventing more than 2 °C global warming. Current policies will create a mitigation gap of up to 19 GtCO₂ (28% of the projected 2015–2050 light-duty vehicle fleet emissions).

2015–2050 US light-duty fleet cumulative CO₂ emissions versus CO₂ budget under prospective future developments. a,b, Baseline cases (top dark-blue bar) and changes in emissions associated with increasing LDV travel demand, fuel consumption standards and electrification assuming current fuel economy policy (SAFE standards) (a) and stringent fuel economy policies (CAFE standards for conventional vehicles, along with high vehicle size and weight control) (b). Mitigation gap refers to the difference between the 2 °C CO₂ emission budget and the emissions with incorporating the previous strategies. SSP1, sustainability—taking the green road; SSP2, middle of the road; SSP5, fossil-fueled development—taking the highway. Milovanoff et al.

Closing the mitigation gap solely with EVs would require more than 350 million on-road EVs (90% of the fleet), half of national electricity demand and excessive amounts of critical materials to be deployed in 2050—a scenario considered unrealistic. The total proportion of EVs currently on the road in the US is about 0.3%. The paper is published in the journal Nature Climate Change.

A lot of people think that a large-scale shift to EVs will mostly solve our climate problems in the passenger vehicle sector. I think a better way to look at it is this: EVs are necessary, but on their own, they are not sufficient.

—Alexandre Milovanoff, lead and corresponding author

Milovanoff and his supervisors, Professors Daniel Posen and Heather MacLean, ran a detailed lifecycle analysis of what a large-scale shift to EVs would mean in terms of emissions and related impacts. As a test market, they chose the United States, which is second only to China in terms of passenger vehicle sales.

The team built computer models to estimate how many electric vehicles would be needed to keep the increase in global average temperatures to less than 2 C above pre-industrial levels by the year 2100, a target often cited by climate researchers.

The team developed a two-staged scenario-based assessment. First, the researchers used the Shared Socioeconomic Pathways (SSPs) to define US LDV fleet CO₂ emission budgets that are consistent with a 2 °C climate goal under different assumptions of prospective global societal developments. Second, they used a fleet-based life-cycle assessment and vehicle turnover model of US LDVs to estimate the prospective life-cycle CO₂ emissions of the fleet under current business-as-usual policies as well as under high electrification scenarios.

The researchers examined the impact of vehicle characteristics (for example, weight and fuel consumption) on LDV fleet CO₂ emissions and then used a backcasting procedure to quantify the timing and volumes of EVs required to remain within suitable CO₂ emission budgets, the resulting electricity use and potential impacts on the electricity system, and the material flows of the electric batteries.

Among the major findings:

• Current policy and electrification targets are insufficient to remain within a suitable US LDV CO₂ emission budget consistent with a 2 °C target. The team estimated 2015–2050 LDV sectoral carbon budgets of 44–50 GtCO₂ between the SSPs. If the US LDV fleet stays constant (in characteristics, stock and travel demand) until 2050, 51 GtCO₂ would be emitted from 2015 to 2050, creating a mitigation gap of 1–7 GtCO₂. The high end of this range exceeds total US CO₂ emissions in 2017 (5.2 Gt), while the low end is half the annual US transportation emissions (1.8 Gt).

  The expected growing travel demand of LDVs from increasing population and economic development broadens the mitigation gap by up to 20 GtCO₂, while the minor fuel consumption improvements of the SAFE standards reduce it by 1 GtCO₂. With no additional policies, electrification of US LDVs following the EV30@30 campaign could bring emission reductions of 7–8 GtCO₂ with a 2018 electricity emission factor, and up to 14 GtCO₂ emission reductions with 100% renewable electricity sources—still insufficient to bridge the mitigation gap.

• Only a combination of feasible stringent policies on fuel economy (20% reduction in new conventional vehicle average fuel consumption between 2019 and 2050) and on weight and size (25% reduction in new vehicle average weight between 2019 and 2050) together with 100% renewable electricity could bridge the mitigation gaps.

• Under a business-as-usual LDV fleet and current policies, up to 351 million EVs would need to be on the road in the US in 2050—up to 90% of the on-road LDV fleet—to remain on target. Attaining this EV penetration would require a 100% market share of EVs (or up to 28 million EVs) by 2050, or possibly as early as 2035.

• EV deployment consistent with a 2 °C target under current policies would be even higher than the current, most optimistic, deployment targets. This brings up the critical issue of what the associated infrastructure and material needs would be.

• A fleet of 350 million on-road EVs in the United States could imply an annual electricity demand of up to 1,730 terawatt hours (TWh)—equivalent to 41% of the 2018 annual national electricity generation (4,200 TWh in 2018). Not only would electricity demand increase but the shape of the demand could be altered significantly.

• A high level of EV deployment would require coordination between the EVs and their driving/charging behaviors. This coordination necessitates extensive deployment of the appropriate charging infrastructure and tailored incentives to adjust driving/charging behaviors, such as smart contracts between EV drivers and electricity suppliers.

  It is therefore crucial that EVs are integrated within a broader framework to ensure that their deployment reduces CO₂ emissions without causing technical instability to power systems. This will come at the cost of deploying a large amount of renewable-based electricity, ‘smart’ infrastructure and behaviors.

  —Milovanoff et al.

Finally, there are technical challenges to do with the supply of critical materials, such as lithium, cobalt and manganese for batteries. Without drastic changes to EV battery material composition or major improvements to the recycling processes of the used batteries, up to 5.0, 7.2 and 7.8 Mt respectively of lithium, cobalt and manganese would need to be extracted between 2019 and 2050 for the US LDV fleet alone—8% and 29% of the identified world terrestrial resources of lithium and cobalt in 2019.

Meeting CO₂ budgets will require a move from technology-oriented policies to activity-oriented policies to provide better substitutes for LDVs, such as transit-oriented land-use policies, deployment of new public transport options, innovative taxes on fuel, parking, congestion and road use, and subsidies for public transportation. Interests in autonomous vehicles or ride-hailing should be scrutinized, as it is unclear whether they would reduce or increase vehicle kilometres travelled, and investments in such technologies should not come at the expense of public transit development and effective strategies to reduce CO₂ emissions.

‘Vehicle’ is, however, a byword for independence and opportunities, and reducing its use creates challenges for social development. Tackling climate change is not a one-country, one-sector or one-technology job. It will be the achievement of extensive system-based analysis, thorough planning and effective implementation. EVs offer an exceptional opportunity to reduce CO₂ emissions. But electrification is not a silver bullet, and the arsenal should include a wide range of policies combined with a willingness to drive less with lighter, more efficient vehicles.

—Milovanoff et al.

Resources

• Milovanoff, A., Posen, I.D. & MacLean, H.L. (2020) “Electrification of light-duty vehicle fleet alone will not meet mitigation targets.” Nat. Clim. Chang. doi: 10.1038/s41558-020-00921-7