A new analysis by the NGO Transport & Environment (T&E) concludes that diesel cars emit more CO2 than equivalent cars on a full lifecycle basis—i.e., accounting for the emissions generated during production of the vehicle and the fuel.
According to the T&E analysis, an average diesel car produces emits 3.65 tonnes more CO2 than an equivalent gasoline car over its lifetime due to a more energy-intensive refining of the diesel fuel; more materials required in the production of heavier and more complex engines; higher emissions from biodiesel blended in the diesel fuel; and longer mileage because fuel is cheaper.
To derive the emissions figure, T&E said that it made a number of assumptions for their calculations:
The average gasoline lifetime driving distance of 175,000 km (108,740 miles) is taken as the starting point.
The average diesel car is driven longer, however, only 4% of this is due to the lower fuel price (rebound effect). T&E adds an additional 7000 km (4,350 miles) to the diesel lifetime distance to account for this.
T&E used the latest real-world fuel consumption figures for diesel and gasoline: 6.3 l/100 km (37.3 mpg US) and 7.1 l/100 km (33.1 mpg US), respectively.
To account for biodiesel effects, T&E assumed a conservative estimate of 5% biodiesel content. The composition of the biodiesel itself uses the average shares of rapeseed oil (48%), palm oil (27%), waste oils (15%), soya oil (5%), tallow & grease (4%), etc.
Similarly, a 5% bio-blend is assumed in gasoline for consistency, using the EU average shares taken from ePure: corn (38%), wheat (37%), sugars (14%), etc.
The carbon intensity of both biodiesel and ethanol is derived by adding ILUC values (the Globiom EC study) to the direct carbon intensity of different feedstocks.
Extra manufacturing emissions are taken to be 5% of the average 5 tonnes of CO2.
For diesel and gasoline shares of B7 and E95, diesel and gasoline specific densities, energy contents and JRC-derived overall well-to-wheel (WTW) carbon intensity factors are used.
In Europe, the car market is skewed in favor of diesels through regulation and tax policies. Whereas the diesel share in Europe is around 50%, it is a niche product in the rest of the world. Europe buys 7 out of 10 diesel cars and vans sold globally while less than 1% of new vehicles sold in the US are diesel and in China, the world’s largest vehicle market, diesel represents less than 2%.
T&E attributed Europe’s diesel share to three main causes:
Distorted national fuel and vehicle taxes. Diesel fuel is taxed between 10% and 40% less than gasoline in most countries. This “diesel bonus” cost national budgets almost €32 billion in lost tax revenue in 2016 alone.
Unfair EU Euro emission standards that for decades allowed diesel cars to emit more NOx than gasoline cars. This has been exacerbated by the use of obsolete tests (recently updated) and ineffective regulatory oversight.
Biased CO2 regulations that set weaker targets for carmakers producing bigger and heavier diesel vehicles.
Going forward, it is could be more appropriate to compare diesel vehicles with alternative low-emission and zero emission powertrains. The most recent and comprehensive lifecycle analysis in this regard has been undertaken by VUB MOBI… The LCA model includes well-to-tank emissions (raw materials, refining, production including components and assembly, and distribution) and tank-to-wheel emissions (use, as well as maintenance and road infrastructure). The analysis demonstrates that the lifetime CO2 emissions of plug-in hybrids and electric vehicles on different electricity mixes are already substantially lower than comparable diesel vehicles. The benefit will continue to increase in the coming years, as more low-carbon and renewable electricity enters European electricity mixes.—T&E study
Accounting for production emissions. In addition to highlighting the regulatory and tax policies that have helped to drive diesel market share in Europe, the T&E study also indirectly opens the provocative question of how to account for greenhouse gas emissions during the production phase.
This is emerging as more of a factor in a comprehensive greenhouse gas control policy as the push for lightweighting to reduce on-road fuel consumption is driving the adoption of lighter metals—but metals that also carry with them a higher carbon footprint.
The steel industry, for example, has been making this argument for about 10 years now. As one example, the Steel Market Development Institute (SMDI) claims that the use of AHSS (advanced high-strength steel) reduces a vehicle’s structural weight by as much as 25% and can cut total life cycle CO2 emissions by up to 15% more than any other automotive material. According to SMDI, while the greenhouse gas emissions from the production of steel are in the range of 2.0-2.5 kg CO2e/kg of material, the range for aluminum is 11.2-12.6, and the range for magnesium from 18-45.
As another factor, the production of EV battery packs—especially in long range EVs—adds to the production-side carbon burden of those vehicles.
According to Greg Archer, Director, Clean Vehicles at T&E, T&E is in favor of eventually shifting to a full lifecycle as the basis for future car CO2 regulations—but not until after 2030.
We believe that given the relatively low level of EV penetration before 2030 (probably around one-third to one-half of new sales) and the need to incentive this shift, a tailpipe metric remains appropriate for the post 2020 regulation for 2025 and 2030 targets. Until then fuels and vehicles should be regulated separately. This is because the auto industry could not be fully responsible for their targets otherwise.
Beyond 2030, the tailpipe emissions become an increasingly small share of the total emissions and production emissions more so (especially the processing of raw materials) so a life-cycle metric should be used. To facilitate this, the post-2020 regulation should include a requirement to develop a life cycle assessment (LCA) approach and a mandatory reporting requirement for manufacturers. In this way data could be assembled and methodologies refined such that by 2025 (when a post 2030 regulation will begin to be discussed) there is a baseline of evidence and experience on which to base a new LCA regulation. We would not design regulations to combine different environmental issues and keep CO2 and air pollution regulations separate.
T&E is not in favor of WTW (well-to-wheel approaches) because the target is shared between carmakers and fuels suppliers. If one party fails to deliver the other will not be willing to do more—the target will simply be missed regulating the sectors separately is the only practical form of implementation.—Greg Archer