Sustainable production and consumption are categorized as target 12 in the United Nations’ Sustainable Development Goals. The “sharing economy” has been developing globally as a new consumption style, and it is often recognized as being environmentally friendly by both consumers and service providers. Several aspects of the practice, such as the avoidance of new production, can reduce the impact to the environment. However, additional factors, such as the expansion of consumption, namely rebound effects, can increase the impact to the environment. Although many variables exist to determine the total impact of sharing services on the environment, additional and rebound effects and the uncertainty of influential variables have not been well considered. In this study, we aim to reveal the conditions that car-sharing practices place in increasing or decreasing environmental loads, and to identify the significant influential factors on the environment imposed by car-sharing services. We analyze the CO₂ emission of car sharing by considering various influential factors and their distributions. Furthermore, we consider differences in car size, fuel type, ownership condition, and several other factors in the simulation. The distribution of each variable is determined, and a Monte Carlo simulation is conducted. The CO₂ emissions from the production and operational stages over a 10-y period are estimated. The simulation is conducted with sensitivity analysis to identify the variables that contribute significantly to the total CO₂ emission. In some cases, the CO₂ emission involved in car sharing exceeded cases in which car sharing is not practiced. Among those cases, although the main contributor to the total CO₂ emission is in the operational stage, CO₂ emission from the production stage increased the amount of emission. It is discovered that the number of cars increased significantly during the target 10 y after sharing is introduced in some cases. These results indicate a high probability that car sharing can achieve CO₂ reduction, but the increase in CO₂ emission can occur under certain conditions. Additionally, the sensitivity analysis shows that the main determinants of CO₂ emission are the ratio of people who eliminated their private cars, degree of rebound effect, and increasing ratio of number of cars introduced to car-sharing practices. This suggests that whether car sharing becomes environmentally friendly depends substantially on consumer behavior and the manner in which sharing services are operated.

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