Changes in the carbon mitigation responsibility of Japan's capital city, Tokyo – analysis of power supply shocks due to nuclear power plant accidents

Abstract

Tokyo is the capital of Japan and the hub of the country's economic and administrative activities. To maintain the momentum of sustained economic growth, Tokyo is transforming the structure of its economic activities, production efficiency, and consumption patterns. Consequently, the supply and demand structure of energy and material in the city has been changing over time with a dramatic increase in the external dependency of supply. In particular, Tokyo depends on the supply of the Tokyo Electric Power Company (TEPCO), which has power plants outside of Tokyo's boundaries. However, TEPCO suspended its nuclear power plants for inspection purposes in 2003. Kashiwazaki-Kariwa Nuclear Power Plant was suspended following Niigata Prefecture Chuetsu-oki Earthquake in 2007; the Fukushima Nuclear Power Plant (the first and second power plants) was suspended following the Great East Japan Earthquake in 2011. In this study, we analyze the changes in the carbon mitigation responsibility of Tokyo, the capital of Japan, after the electricity supply shock caused by the nuclear power plant accident and examine how dependence on electricity supply affects CO2 emissions. We compare CO2 emissions in terms of 1) the changes in Tokyo's electricity supply, 2) the long-term changes in the local economy (flows of goods and services) in 1990, 1995, 2000, 2005, 2011, and 2015, and 3) different carbon accounting methods applied to consumption-based emissions. In this study, we have adopted a method that is based on four system boundaries to identify and compare per capita CO2 emissions from 1990 to 2015 using data from Tokyo's statistical data. Results show that although CO2 emissions associated with Tokyo's electricity consumption fluctuated significantly due to the suspension of the nuclear power plant, there was no significant change in Tokyo's consumption-based emissions. Since Tokyo's consumption structure has remained steady despite these major changes in electricity supply, we assume that Tokyo's emission responsibility will not change unless there is a major switch to lower carbon goods and services consumed in the city.