*4.3. Policy Recommendations*

Targeting the trend towards smaller households and under-occupation of homes in the EU and globally is a key option to reduce per capita carbon and energy contributions, with a higher mitigation potential compared to efficiency improvements such as upgrading the thermal insulation or more efficient appliances [42,63]. Understanding needs and expectations about personal space as well as changing social norms [18] are key for the upscaling of "downsizer homes" [63] and other alternatives to encourage within household sharing. Household sharing has an important gender dimension [53] as well; sharing may support the depersonalization of objects allowing for them to be managed and used jointly, thus encouraging even more (and more gender equal) sharing [53].

Yet, the trend of smaller households results from a myriad of processes, some of which cannot be reversed (e.g., falling birth rates or liberation from norms), or which we consider valuable for other reasons (e.g., female emancipation, financial independence or residential autonomy) [48,61]. For example, higher divorce rates worldwide may result in an increase of energy use and GHG emissions per capita [13]; however, the freedom to divorce is also a matter of human rights and social justice. This makes it crucial for policy interventions to realize the complexity of household dynamics and the inter-connections with social and environmental wellbeing.

Proximate causes of the reduction in household sizes worldwide include lower fertility rates, higher divorce rates and a decline in the frequency of multi-generational families with increasing non-family provision of care among others [61,64]. There is some evidence that the trend of decreasing fertility rates and increasing divorce rates is reversing since the early 2000s [65,66], which may also stabilize or even reverse the trend of smaller households. This suggests that the trend towards smaller families over the past half century did not result from a lasting change of family preferences, but rather

from a change in women's roles and labor market participation when institutions and partnerships had not yet adapted [65]. To successfully promote parenthood and female labor force participation, there is a need for a strong investment in childcare services, flexible workplace support and other family support [65,66]. Such policies may help reconcile work and family responsibilities and promote gender equity [65].

Additional social and psychological factors that may have influenced the reduction in household sizes include liberation from strict norms, less religiosity and increased importance of individual autonomy, self-actualization and privacy [48,61]. Support and increased visibility [67] for alternative household types—such as intentional communal living—may encourage larger households, which share lifestyles, cultural elements and common sense of purpose. Such alternative forms of living may thus be less challenging in terms of these social and psychological factors [12], compared to traditional family living. Yet alternative living arrangements may also be associated with difficulties in negotiating common and personal items, space and time [9]. Partnerships between policymakers and sharing initiatives may help tackle such difficulties by alleviating structural and institutional constraints and reducing social distance (e.g., by fostering care for the community) and geographical distance (e.g., by improving connectivity), which impede sharing [9,11]. Sharing emerges as an opportunity to act collectively on growing social, political and environmental awareness and steadily transforms social norms and routines [68].

The complexity of household dynamics and the low household economies of scale in high-carbon consumption domains such as transport encourage the consideration of additional ways to share resources between households as well. For example, while sharing a car may reduce the energy use and emissions associated with travel *within* the household (particularly in car-dependent areas outside urban cores [22]), in the presence of an excellent public transport system, the mitigation potential may actually be higher through sharing *between* households. Further research on household sharing in the context of public infrastructure and sharing initiatives at a higher spatial resolution—in both urban and rural context—is needed to explore the carbon mitigation potentials associated with sharing. Such wider sharing practices for de-carbonization and low energy demand require the provision of social and technological infrastructure such as investment in public spaces, green areas, mass transportation and new forms of peer-to-peer sharing [9,24]. The establishment of collective systems (e.g., universal basic services [69])—as opposed to highly individualized energy service delivery—also enables more resilient societies and prevents future emission lock-in [70].

In this paper, we explore possible impacts of household dynamics on per capita emissions, and examine difference in within household economies of scale across EU countries. Our main finding is that household economies of scale vary substantially across consumption categories, urban and rural typology and EU countries. We identify potential explanations associated with the sharing potential of various products and services, contextual differences in terms of social and cultural norms, geographic context, infrastructural and political context. Targeting trends towards smaller households and under-occupation of homes and encouraging sharing offers substantial potential to mitigate climate change with already available technologies and infrastructure.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/13/8/1909/s1, SM1: Household Budget Surveys, SM2: Descriptive statistics by countries, SM3: Eurostat statistics, SM4: Total carbon and energy footprint determinants, Supplementary spreadsheet including the overview of consumption categories.

**Author Contributions:** Conceptualization, D.I. and M.B.; Formal analysis, D.I.; Funding acquisition, D.I. and M.B.; Investigation, D.I. and M.B.; Methodology, D.I. and M.B.; Software, D.I.; Supervision, M.B.; Visualization, D.I.; Writing—original draft, D.I.; Writing—review and editing, M.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the European Union's Horizon 2020 research and innovation program under Marie Sklodowska-Curie grant agreement, grant number 840454. The authors also received support from the UK Research Councils under the Centre for Research on Energy Demand Solutions.

**Acknowledgments:** We thank the whole EXIOBASE team for the effort to build the database and make it available for other researchers to use. In particular, we would like to thank Richard Wood for his assistance in the early stages of the environmental footprint analysis and Arkaitz Usubiaga-Liaño for his effort in compiling and communication the energy extensions. We would also like to thank Sylke Schnepf and two anonymous reviewers for their valuable feedback.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Data Statement:** The data associated with this paper is available from University of Leeds at https://doi.org/10. 5518/785. The dataset includes the per capita carbon and energy footprint calculations (generated by the authors of this study) together with household and country IDs from the HBS dataset disseminated by Eurostat. Please use the following data citation when referring to the dataset [71]: Diana Ivanova and Milena Büchs (2020): Carbon and energy footprints of European households (EU HBS) University of Leeds. [Dataset]. https://doi.org/10.5518/785.
