The paper investigates the impact of unexpected events, specifically the 2008 global financial crisis and the 2011 Tohoku earthquake and tsunami, on Japan's carbon emissions. Rapid economic growth in preceding decades raised concerns about the sustainability of energy systems and their environmental impact. National energy systems and their associated greenhouse gas (GHG) emissions have become central to international environmental policy, notably the 2015 Paris Agreement. While long-term economic change and policy can shape energy mixes and GHG emissions, unexpected events can have profound and immediate effects, potentially reversing established emission pathways. The 2008 financial crisis, for example, caused a short-term decline in global emissions, but these emissions quickly rebounded. Japan, with its limited natural resources and dependence on energy imports, presents a compelling case study. Despite being a major industrialized nation committed to GHG emission reduction targets under the Kyoto Protocol and the Paris Agreement, Japan's energy mix experienced major shifts due to both planned policies and unanticipated events. Nuclear power historically played a significant role but was drastically impacted by the Fukushima Daiichi nuclear disaster following the 2011 earthquake. This disaster created an immediate energy supply shortage and a long-term shift away from nuclear power, necessitating increased reliance on fossil fuels, particularly coal. The study emphasizes the need for a nuanced understanding of how these events affected emissions at national and regional levels, aiming to inform the design of more effective climate change mitigation strategies.

The authors review existing literature on the impact of unanticipated events (financial crises and natural disasters) on energy systems and GHG emissions. Studies show that such events can rapidly alter production and consumption patterns, leading to short-term emission reductions or increases. However, the literature highlights the frequent rebound effect, where emissions quickly return to pre-event levels or even surpass them. Previous research on Japan's emission drivers often focused on national-level analysis, neglecting the sub-national variations crucial for effective policy design. This study addresses this gap by providing a regional-level analysis of emission patterns and drivers in Japan, acknowledging the existing literature’s focus on national level analysis and the absence of thorough sub-national studies.

The study quantifies national and regional carbon emission patterns for Japan's major economic sectors (manufacturing, construction, mining, energy supply, services, agriculture, forestry, and fisheries) from 2007 to 2015. The data encompass the periods before and after the 2008 financial crisis and the 2011 Tohoku earthquake. The Logarithmic Mean Divisia Index (LMDI) method is employed to decompose the effects of various drivers on emissions. Aggregate regional and sectoral carbon emissions were estimated using data on electricity consumption and the three major fossil fuels (coal, crude oil, natural gas). The 47 Japanese prefectures were aggregated into ten regions based on the boundaries of the ten major Electricity Power Suppliers. Electricity-related emissions were allocated to sectors based on their electricity consumption. The LMDI method was used to decompose the effects of ten driving forces: population, per capita GDP, economic structure, energy intensity, energy mix (by fuel), and emission intensity (by fuel). Equations were used to estimate the effects of these drivers on carbon emissions changes between 2007 and 2015. The study acknowledges limitations in data availability, particularly concerning the allocation of electricity emissions and the lack of detailed technology-specific emission data. Despite this limitation, the study uses available data on coal consumption and power generation technology promotion to make estimations at the regional level.

The study reveals significant fluctuations in Japan's total emissions at both national and regional levels around the 2008 financial crisis and the 2011 earthquake, with more pronounced changes following the earthquake. Nationally, emissions decreased in 2008 and 2011, followed by increases in subsequent years. A decline of 35.58 MtCO2 was estimated for 2007–2010, primarily due to per capita GDP and oil's share in the energy mix. Conversely, a 27.06 MtCO2 increase was observed in 2012–2015, mainly driven by per capita GDP, industrial value added, and coal's share in the energy mix. Regionally, most areas experienced emission declines after both events, except for Okinawa after the 2008 crisis and Hokkaido and Okinawa after the 2011 earthquake. Coal-related emissions increased significantly after 2011 in several regions (Kyushu, Tohoku, Kansai). Manufacturing was the largest source of emissions across most regions. The analysis of emission drivers reveals that economic effects dominated in 2009–2010, energy structure effects were most significant in 2012–2013, and energy intensity played a larger role from 2014 onwards. The shift towards greater coal use after the 2011 earthquake to mitigate the energy shortage following the Fukushima Daiichi nuclear disaster was a significant driver of emission increases. This finding highlights the substantial effect of unexpected events on Japan’s energy mix and overall emissions. Improved energy efficiency (energy intensity) consistently contributed to emission declines across most regions.

The findings demonstrate the significant impact of both the 2008 financial crisis and the 2011 Tohoku earthquake on Japan's carbon emissions, illustrating how unexpected events can disrupt emission reduction efforts and alter energy system trajectories. The shift toward increased coal use after the 2011 earthquake, driven by the energy shortage following the Fukushima disaster, highlights the vulnerability of energy systems to unexpected events. The study underscores the need for spatially and temporally differentiated, adaptive approaches to emission mitigation. While the analysis points to the manufacturing sector and coal-related emissions as priority areas for sub-national mitigation plans, it also reveals considerable regional variability in emission drivers and patterns, emphasizing the need for context-specific strategies.

This research reveals significant fluctuations in Japan's carbon emissions following the 2008 financial crisis and the 2011 Tohoku earthquake, highlighting the vulnerability of energy systems to unexpected shocks. The study's key contribution lies in its regional-level analysis, which reveals substantial spatial and temporal heterogeneity in emission drivers and patterns. This underscores the need for targeted, adaptive climate change mitigation strategies that account for these variations. Future research should explore the impact of the COVID-19 pandemic on regional emissions and investigate the effectiveness of diverse mitigation strategies at finer spatial scales.

The study acknowledges limitations in data availability, particularly regarding the precise allocation of electricity emissions to specific regions and the lack of data on plant-specific technologies and fuel consumption. This restricts a more detailed bottom-up analysis of emissions by technology, which would enhance the precision of regional-level mitigation planning. The regional aggregation based on electricity company coverage is relatively coarse and might mask variations at finer spatial scales (prefectures or cities).