Cities are recognised as central to determining the sustainability of human development. However, assessment concepts that are able to ascertain whether or not a city is sustainable are only just emerging. Here we review literature since the Sustainable Development Goals (SDGs) were agreed in 2015 and identify three strands of scientific inquiry and practice in assessing city sustainability. We find that further integration is needed. SDG monitoring and assessment of cities should take advantage of both consumption-based (footprint) accounting and benchmarking against planetary boundaries and social thresholds in order to achieve greater relevance for designing sustainable cities and urban lifestyles.
Sustainable development requires balanced integration of four basic human needs – air (O2/CO2), water, food, and energy. To solve key challenges, such as CO2 fixation, electricity storage, food production, transportation fuel production, water conservation or maintaining an ecosystem for space travel, we wish to suggest the electricity-carbohydrate-hydrogen (ECHo) cycle, where electricity is a universal energy carrier, hydrogen is a clean electricity carrier, and carbohydrate is a high-energy density hydrogen (14.8 H2 mass% or 11-14 MJ electricity output/kg)carrier plus a food and feed source. Each element of this cycle can be converted to the other reversibly & efficiently depending on resource availability, needs, and costs. In order to implement such cycle, here we propose to fix carbon dioxide by electricity or hydrogen to carbohydrate (starch) plus ethanol by cell-free synthetic biology approaches. According to knowledge in the literature, the proposed artificial photosynthesis must be operative. Therefore, collaborations are urgently needed to solve several technological bottlenecks before large-scale implementation.
By applying a single dataset (i.e., panel data at a national level) and a single analytical framework (i.e., a dynamic mathematical model), I compared religious (REL) and secular (SEC) ethics in two ways: as feasible strategies (i.e., with realistic parameter values such that a strategy can achieve its goal) and as reliable strategies (i.e., with a tight statistical relationship between a strategy and its goal). In both cases, the goal is to achieve environmental sustainability, but with different precepts and principles applied within different perspectives: global vs. local sustainability, individual feelings vs. social pressures as determinants of pro-environmental behavior, and long-run vs. short-run sustainability. Analytical results (feasibility) showed that REL are overall more feasible than SEC and, specifically, REL are more likely to affect the many pro-environmental behaviors required to achieve global sustainability, whereas SEC to affect some pro-environmental behaviors required to achieve local sustainability; REL are more likely to affect pro-environmental behaviors based on individual feelings and social pressures from small communities, whereas SEC to affect pro-environmental behaviors based on social pressures from large communities; REL are more likely to solve collective-action problems to achieve short-run sustainability, whereas SEC to solve collective-action problems to achieve long-run sustainability. Statistical results (reliability) based on 32 random- and between-effects regressions support these results and, particularly, REL and SEC were complementary in time (e.g., for REL, short-run sustainability is more reliable than long-run sustainability; for SEC, long-run sustainability is more reliable than short-run sustainability), in space (e.g., for SEC, local sustainability is more reliable than global sustainability), and in society (e.g., for REL, individual feelings are more reliable than social pressures).