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Study finds that replacement programs that reduce vehicle lifetime can result in increased lifecycle CO2 emissions
1 February 2011
|Effects of changes in the average lifespan of ordinary passenger cars newly registered between 1990-2000 on total induced CO2 emissions in 2000. Credit: ACS, Kagawa et al. Click to enlarge.|
Extending, not shortening, the lifetime of a vehicle helps to reduce life-cycle CO2 emissions throughout the supply chain, according to a new study based on a case study of Japanese vehicle use during the 1990-2000 period published in the ACS journal Environmental Science & Technology. Conversely, encouraging shortened vehicle lifetime via vehicle replacement schemes can result in higher total-induced greenhouse gas emissions, the authors found.
Empirical results also revealed that even if the fuel economy of less fuel-efficient ordinary passenger vehicles were improved to levels comparable with those of the best available technology, i.e. hybrid passenger cars currently being produced in Japan, total CO2 emissions would decrease by only 0.2%. They also found that extending the lifetime of a vehicle contributed to a moderate increase in emissions of criteria pollutants (NOx, HC, and CO) during the use phase of the vehicle.
Vehicle replacement schemes such as the “cash for clunkers” program in the US and the “scrappage scheme” in the UK have featured prominently in the economic stimulation packages initiated by many governments to cope with the global economic crisis—at least 13 countries have deployed such schemes. While these were designed as economic instruments to support the vehicle production industry, governments have also claimed that these programs have environmental benefits such as reducing CO2 emissions by bringing more fuel-efficient vehicles onto the roads.
However, little evidence is available to support this claim as the few existing studies have failed to systematically consider the trade-offs between fuel efficiency improvement and additional vehicle fleet production due to the replacement....This paper focuses on the gasoline vehicle replacement schemes of Japan, and we statistically estimate the vehicle lifetime distributions addressing the effect of decreasing the life of passenger cars on the mitigation of global warming and the improvement of air quality. It should be noted that car ownership of diesel passenger vehicles amounted to only about 8% of total passenger vehicles in 2000 in Japan and that gasoline passenger vehicles have been more popular than diesel passenger vehicles since 1978.—Kagawa et al.
Extending vehicle life reduces the number of new vehicles sold, with an associated decrease in energy consumed for vehicle production. The increased lifetime of cars negatively affects the fuel efficiency average of the fleet, with negative environmental implications. Similarly, the researchers note, policies directed toward extending vehicle lifetime would be subject to two types of rebound effects:
- With reduced spending on new vehicles, consumers would spend their additional disposable income on other goods and services and generating additional carbon emissions in the sectors that produce them.
- The second rebound effect might arise if consumers buy more fuel-efficient vehicles and the energy cost per unit distance decreases due to improved fuel economy, vehicle owners may be inclined to drive farther, which may increase overall energy consumption.
To the best of our knowledge, this study is the first attempt to empirically investigate the impacts of the lifetime shifts of a vehicle on the life-cycle CO2 emissions and other air pollution throughout the supply chain and argue the trade-off relationship between car lifetime and desirable fuel efficiency level from the point of view of the life-cycle CO2 emissions.—Kagawa et al.
The authors had previously developed a dynamic energy accounting model with specified product lifetime distributions. In this study, they modified that framework to analyze the effects of shortening of lifetime of less fuel-efficient ordinary passenger cars on CO2 emissions induced by motor vehicle manufacturing, CO2 emissions due to motor vehicle use (i.e., fuel combustion), and CO2 emissions generated throughout the supply chain.
Among their findings:
CO2 emissions associated with motor vehicle manufacturing substantially decrease as car lifetime is extended, even though gasoline combustion- derived CO2 emissions increase. The reason for this is that an extension in motor vehicle lifetime has the effect of reducing the number of new motor vehicles sold, thereby reducing the number of motor vehicles produced and the amount of CO2 emissions attributable to motor vehicle manufacturing.
This extension in car lifetime does result in an increase in the number of old and less fuel-efficient vehicles still in service, increasing the CO2 emissions from the vehicle fleet still on the road.
However, total induced CO2 emissions, i.e. the combined emissions from motor vehicle production, gasoline refining, gasoline combustion, and other services, decrease in response to an extension in motor vehicle lifetime. This finding implies that the product lifetime extension scenario would clearly contribute to a reduction in carbon emissions, the authors said.
A shorter motor vehicle lifetime would result in an accelerated car replacement cycle, which would lead to more new and fuel efficient motor vehicles on the road, which would in turn reduce gasoline combustion-derived CO2 emissions. However, the reductions achieved in this manner are rendered less significant when considered against the relative contribution of the CO2 emissions associated with the production of new motor vehicles. The net result would be an increase in total CO2 emissions.
To completely offset the emissions increase attributable to a one-year reduction in motor vehicle lifetime, an improvement in the fuel efficiency of approximately 12.7% would be required.
A one-year reduction in vehicle lifetime would increase the demand by approximately 8.3%. Under this scenario, the activities of vehicle manufacturers would have an adverse effect on the environment unless they were able to achieve a fuel-efficiency improvement equivalent to approximately 1.5 times the rate of the increase in demand.
The market share of hybrid cars would have to increase significantly, to 7.3%, in order to completely offset the higher levels of emissions discharged due to a one-year decrease in the average lifetime of fuel-inefficient ordinary passenger cars. An important point is that even if the market share of the hybrid cars increased to 7.3%, it would conversely harm the environment in case of decreasing the lifetime larger than one year, because the CO2 increase associated with car production exceeds the CO2 decrease associated with car driving.
If the 2000 market shares of hybrid cars were 14.1%, a one-year decrease in lifetime will reduce life-cycle CO2 emission in 2000 by 0.6%. A reduction of more than 2.1 years lifetime reduction conversely increases the CO2 emission under the 14.1% market share of hybrid cars.
Overall, the results of this study show that, at least for gasoline-powered passenger cars, the belief that a motor vehicle-dependent society can achieve marked reductions in CO2 emissions only through improved fuel efficiency may be illusory, particularly since the current policies are directed at encouraging shorter motor vehicle lifetimes and, consequently, increased total emissions, which will steer Japan further away from achieving its Kyoto target. To reduce the volume of emissions by shortening the lifetime of the passenger car, government incentives are required after quantitative clarification of both fuel efficiency levels and the market share of environmentally friendly vehicles needed to offset the CO2 emissions and health-relevant air pollution associated with shorter passenger car lifetime.—Kagawa et al.
Shigemi Kagawa, Keisuke Nansai, Yasushi Kondo, Klaus Hubacek, Sangwon Suh, Jan Minx, Yuki Kudoh, Tomohiro Tasaki, and Shinichiro Nakamura (2011) Role of Motor Vehicle Lifetime Extension in Climate Change Policy. Environ. Sci. Technol., doi: 10.1021/es1034552
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