The sustainable development goals (SDGs) launched by the United Nations (UN) set a new direction for development covering the environmental, economic, and social pillars. Given the complex and interdependent nature of the socioeconomic and environmental systems, however, understanding the cause-effect relationships between policy actions and their outcomes on SDGs remains as a challenge. We provide a systematic review of cause-effect analysis literature in the context of quantitative sustainability assessment. The cause-effect analysis literature in both social and natural sciences has significantly gained its breadth and depth, and some of the pioneering applications have begun to address sustainability challenges. We focus on randomized experiment studies, natural experiments, observational studies, and time-series methods, and the applicability of these approaches to quantitative sustainability assessment with respect to the plausibility of the assumptions, limitations and the data requirements. Despite the promising developments, however, we find that quantifying the sustainability consequences of a policy action, and providing unequivocal policy recommendations based on it is still a challenge. We recognize some of the key data requirements and assumptions necessary to design formal experiments as the bottleneck for conducting scientifically defensible cause-effect analysis in the context of quantitative sustainability assessment. Our study calls for the need of multi-disciplinary effort to develop an operational framework for quantifying the sustainability consequences of policy actions. In the meantime, continued efforts need to be made to advance other modeling platforms such as mechanistic models and simulation tools. We highlighted the importance of understanding and properly communicating the uncertainties associated with such models, regular monitoring and feedback on the consequences of policy actions to the modelers and decision-makers, and the use of what-if scenarios in the absence of well-formulated cause-effect analysis.

Typical applications of LCA assume that the magnitude of life-cycle impact grows proportionally to the volume of demand, while in reality the additional impact due to marginal increase in demand may differ from the average impact. In the literature, the calculation of marginal life-cycle impacts often involves the use of optimization models, where typically the total economic costs are minimized. However, modeling spatially explicit marginal responses of a system involving multiple producers and consumers has not been discussed in LCA literature. In this paper, we demonstrate a spatial optimization technique for modeling marginal responses of a multi-producer, multi-consumer system. Our model determines the optimal production-by-location mix and associated environmental stressor at minimum systems cost. We demonstrate the model using a preliminary case study on blue water consumption by potato. We collected state-by-state data on potato yield, cost of potato production, and water use for irrigation, as well as interstate transportation fuel costs. We also estimated the marginal increase in demand for potato following USDA's recommended diet. The results show that the cradle-to-gate blue water consumption of potatoes based on 2016 demand was 96 m3/ton potato, which changes non-linearly along with the growth of potato demands. In order to meet the USDA's recommended diet, the additional demand on potato (530,000 ton per year) would result in a 29% lower blue water consumption per ton of potato (68 m3/ton) as compared to the average result of the current production system. In addition, we tested the model to analyze the marginal impacts under two scenarios: (1) high fuel tax and (2) high water price. The preliminary results indicate that water pricing is more effective than a fuel tax increase in reducing the marginal blue water consumption of potato based on our scenarios of the recommended diet demand. The results demonstrate that our model can be used to understand the non-linear behavior of marginal effect over demand crease, and for testing alternative policy scenarios involving a system with multiple producers and consumers across regions.

Tom et al. (Environ Syst Decis 1–12, 2015) compared the energy requirements, water footprint, and greenhouse gas emissions of diet regimens recently recommended by the US Department of Agriculture. This editorial comments on a number of challenges related to the use of the results of life-cycle assessment studies to quantify the environmental impacts of dietary shifts.