Why Carbon Dioxide Emissions from Japanese Passenger Cars Peaked in 2001

Reducing carbon dioxide (CO₂) emissions from passenger cars is important for meeting the long-term Japanese target for reduction of greenhouse gas emissions. Further, decomposition analysis of changes in CO₂ emissions is important for policy making. However, there is a case for concern about the reliability and accuracy of the calculation results obtained by decomposition analysis methods in previous studies related to the residual term. A decomposition analysis method was developed so that the residual term was attributed to a related factor. Changes in regional CO₂ emissions from passenger cars in Japan for 1990 to 2008 were then analyzed with this method. CO₂ emission characteristics are influenced by travel distance, number and weight of passenger cars, actual road fuel efficiency, and population. The main reason for the increase in CO₂ emissions for the period 1990 to 2001 was the increase in the number and weight of passenger cars in all regions of Japan. The main reasons for the decrease in CO₂ emissions in all regions of the country for the period 2001 to 2008 were the decrease in travel distance per passenger car and improvement in actual road fuel efficiency. Population movement from nonmetropolitan regions toward Tokyo and Osaka affected total CO₂ emissions but not significantly.