Increasing single households challenges household decarbonization in Japan

• Quantify carbon footprints in single households, revealing the increased emissions. • Identify gender-specific carbon footprint differences within single households. • Propose targeted sustainability policies for energy efficiency and consumption. • Analyze future carbon footprint trends under different SSP scenarios. In light of societal shifts such as an aging population, delayed marriages, and higher rates of divorce, there's a notable rise in solitary living, affecting society, the economy, and the environment. To understand the implications of these demographic shifts, our research examines the nexus between solo living and its broader social-environmental consequences. Using Japan, one of the countries with the highest proportion of the elderly, as a reference, we explore the temporal fluctuations, gender-specific variances, and long-term trends in carbon footprints influenced by alterations in consumption behaviors. Results indicate that housing energy and food consumption remain the dominant carbon footprint contributors across all demographic sectors. Interestingly, single households present higher carbon footprints than non-single households, with those of single females surpassing their male counterparts due to increased household energy use and expenditures on clothing and healthcare. Following the demographic shifts, single households are expected to account for approximately 31.1% of Japan's emissions from households by 2040, challenging national decarbonization efforts due to their higher per capita emissions. This highlights the imperative for bespoke strategies, especially in resource allocation and sharing, to address the solo living challenge and ensure congruence with Japan's sustainability and decarbonization goals.