摘要：One of the goals of the US Consumer Assistance to Recycle and Save (CARS) Act of 2009,
more commonly known as 'Cash for Clunkers', was to improve the US vehicle fleet fuel
efficiency. Previous studies of the program's environmental impact have focused mainly on
the effect of improved fuel economy, and the resulting reductions in fuel use and emissions
during the vehicle use phase. We propose and apply a method for analyzing the net effect
of CARS on greenhouse gas emissions from a full vehicle life cycle perspective,
including the impact of premature production and retirement of vehicles. We
find that CARS had a one-time effect of preventing 4.4 million metric tons of
CO2-equivalent emissions, about 0.4% of US annual light-duty vehicle emissions. Of these,
3.7 million metric tons are avoided during the period of the expected remaining life of the
inefficient 'clunkers'. 1.5 million metric tons are avoided as consumers purchase vehicles that
are more efficient than their next replacement vehicle would otherwise have been. An
additional 0.8 million metric tons are emitted as a result of premature manufacturing and
disposal of vehicles. These results are sensitive to the remaining lifetime of the 'clunkers'
and to the fuel economy of new vehicles in the absence of CARS, suggesting
important considerations for policymakers deliberating on the use of accelerated
vehicle retirement programs as a part of the greenhouse gas emissions policy.
