Evaluation of energy-related household carbon footprints in metropolitan areas of Japan

In the Post-Paris Era, urban emissions have received worldwide attention as cities are considered to be responsible for most of the world's environmental footprint. A better understanding of urban CO2 emissions and their related carbon footprints offers benefits to policymakers interested in promoting effective and efficient low-carbon solutions. In particular, a clear determination of direct and indirect emissions inventories (that is, identification of emissions related to specific sources) can provide a valuable baseline for the planning, assessing, implementing, and monitoring of urban mitigation actions. Focusing on the Japanese urban residential sector, this paper uses an established urban database and emission database based on global-related input-output analysis to systematically analyze household carbon footprints related to energy demand, targeting both direct and indirect energy-related CO2 emissions in Japan's megacities. The results reveal the city-specific emissions status of Japan's three major metropolitan areas, showing, for example, that Tokyo is a source of high direct emissions, while Utsunomiya is a significant source of indirect emissions. The study also tentatively concludes that the depopulation of cities can result in higher per capital emissions, both direct and indirect, as they relate to energy demand. Improved sector and spatially explicit information for better mitigation policymaking and environmental education at the urban level is presented. Valuable insights are offered through an in-depth investigation of the relationship between CO2 emissions and urban socioeconomic activities, benefitting future low-carbon city research and practice.