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Weak sustainability (WS) requires that the inclusive wealth (IW) of a place (e.g., the world, a nation, or a sub-national region) be non-decreasing over a long time. The WS framework provides a more complete account of the sustainability of a place than do sustainability indicators or conventional economic measures, such as gross domestic product. However, while many decisions that affect sustainability are made at regional and local levels, the abstract theory of WS was developed without explicit recognition of the porosity of geographic boundaries and the interdependencies of regions. In this paper, we make three contributions: a carefully reasoned defense of IW per capita as the WS criterion, an improved understanding of the relationship between mobility, labor productivity, and regional economic growth, and an empirical application to US counties that demonstrates the feasibility of empirical regional WS assessment by summarizing Jones’ research. This analysis, extending the framework developed by Arrow and co-authors, accounts for more region-specific factors related to population, most notably the labor productivity component of health capital, and assesses IW per capita for all 50 states and 3108 counties in the US from 2010 to 2017. These improved methods revealed substantially more states and counties that were not WS relative to results using the Arrow et al. framework. The not-WS counties exhibited a distinct rural bias, as regional scientists have suspected but, nevertheless, the majority of rural counties were WS. Our work demonstrated that regional WS assessment is feasible, produces results that are consistent with prior expectations based on reasoning and empirical research, and has the potential to provide fresh insights into longstanding questions of regional development. 

Our purpose is to advance a reasoned perspective on the scientific validity of computer simulation, using an example—integrated assessment modeling of climate change and its projected impacts—that is itself of great and urgent interest to policy in the real world. The spirited and continuing debate on the scientific status of integrated assessment models (IAMs) of global climate change has been conducted mostly among climate change modelers and users seeking guidance for climate policy. However, it raises a number and variety of issues that have been addressed, with various degrees of success, in other literature. The literature on methodology of simulation was mostly skeptical at the outset but has become more nuanced, casting light on some key issues relating to the validity and evidentiary standing of climate change IAMs (CC-IAMs). We argue that the goal of validation is credence, i.e., confidence or justified belief in model projections, and that validation is a matter of degree: (perfect) validity is best viewed as aspirational and, other things equal, it makes sense to seek more rather than less validation. We offer several conclusions. The literature on computer simulation has become less skeptical and more inclined to recognize that simulations are capable of providing evidence, albeit a different kind of evidence than, say, observation and experiments. CC-IAMs model an enormously complex system of systems and must respond to several challenges that include building more transparent models and addressing deep uncertainty credibly. Drawing on the contributions of philosophers of science and introspective practitioners, we offer guidance for enhancing the credibility of CC-IAMs and computer simulation more generally. 

Weak sustainability, WS, attempts a comprehensive notion of sustainability, sustaining human welfare directly, or equivalently, sustaining inclusive wealth, IW, sufficient to sustain welfare. Sustainability is, in principle, forever, and accordingly, IW is conceived and assessed in a very long-term context. Given that future outcomes are unobservable, IW assessments are conducted in terms of expectations. However, this introduces pervasive circular reasoning: the calculated value of IW assumes that our expectations will be met, but that is the question. Optimistic expectations (for example) increase calculated IW, which, in turn, increases our confidence that our society is on a sustainable path. Given the logical difficulties of projecting IW into the future, analysts resort to tracking IW at regular intervals through the recent past. This reduces, but does not eliminate, the circularity problem. The signals from tracking IW are less than perfect from a policy perspective: they are too aggregate, perhaps masking impending crises regarding particular resources until it is too late; and too dependent on imperfect markets; and they document the recent past, so policy managers are always playing catch-up. WS-based sustainability policy frameworks include WS-plus, which invokes ad hoc strong sustainability, SS, patches to address threatened resource crises. It may also be possible to allow a degree of WS flexibility for individual jurisdictions within the constraints of a global safe operating space, SOS. 

The objective is to provide an interpretive reading of the literature in resource scarcity and sustainability theory from the nineteenth century to the present time, focusing on shifts that have occurred in problem definition, conceptual framing, research tools applied, findings, and their implications. My reading shows, as one would expect, that the discourse has become more technical and the analysis more sophisticated; special cases have been incorporated into the mainstream of theory; and, where relevant, dynamic formulations have largely supplanted static analysis. However, that is barely scratching the surface. Here, I focus on more fundamental shifts. Exhaustible and renewable resource analyses were incorporated into the mainstream theory of financial and capital markets. Parallels between the resources and environmental spheres were discovered: market failure concepts, fundamental to environmental policy, found applications in the resources sector (e.g., fisheries), and renewable resource management concepts and approaches (e.g., waste assimilation capacity) were adopted in environmental policy. To motivate sustainability theory and assessment, there has been a foundational problem shift from restraining human greed to dealing with risk viewed as chance of harm, and a newfound willingness to look beyond stochastic risk to uncertainty, ambiguity, and gross ignorance. Newtonian dynamics, which seeks a stable equilibrium following a shock, gave way to a new dynamics of complexity that valued resilience in the face of shocks, warned of potential for regime shifts, and focused on the possibility of systemic collapse and recovery, perhaps incomplete. New concepts of sustainability (a safe minimum standard of conservation, the precautionary principle, and planetary boundaries) emerged, along with hybrid approaches such as WS-plus which treats weak sustainability (WS) as the default but may impose strong sustainability restrictions on a few essential but threatened resources. The strong sustainability objective has evolved from maintaining baseline flows of resource services to safety defined as minimizing the chance of irreversible collapse. New tools for management and policy (sustainability indicators and downscaled planetary boundaries) have proliferated, and still struggle to keep up with the emerging understanding of complex systems. 

This article shows how sustainability indicators (SIs) which have proliferated, and downscaled planetary boundaries (DPBs) which have recently emerged, can be used to target remedial interventions. I offer an integrative analysis drawing upon the existing literature, challenging, clarifying, and amending it in some ways, and extending it with new insights. The exposition is couched in the example of pollution control, but the analysis also applies to resource management with only modest amendments. Key conclusions are summarized. (i) In a default case where damage is indifferent to location within the problem shed and transactions costs are trivial, minimizing abatement costs requires that all units face the same marginal price of emissions and can be implemented by price setting at the jurisdictional level or cap and trade in pollution reduction credits. Larger geographic scale tends to reduce the average cost of abatement, an argument for coordination at the problem-shed level. Deviations from the default policy may be appropriate for addressing large point sources and local hot spots where damage is concentrated. (ii) A framework winnowing the proliferation of SIs includes the following principles: for quantitative target setting, SIs should address sustainability in its long-term context; SIs should be measured in ratio scale, whereas ordinal-scale SIs are common; and SIs should be selected for their usefulness in mapping the relationships among emissions, ambient concentrations, and damage. (iii) Target setting requires science-based empirical relationships and social values to assess trade-offs between abatement and its opportunity costs and suggest upper limits on tolerable damage. (iv) PBs that address global public goods can usefully be downscaled to set abatement targets. The PBs are science based and, in their original form, propose replacing social values with imperatives: violating the PB will doom the planet, which is unacceptable given any plausible value system. Given that PB = ∑DPB over all jurisdictions, global trading of credits would minimize costs of honoring the PB. Trade among a willing subset of jurisdictions could minimize the costs of meeting its aggregate DPB. (v) In contrast to most SI approaches, a cost–benefit (CB) approach can deal with substitutability and complementarity among sustainability objectives and evaluate multi-component policies. Net benefits are maximized when the marginal cost of abatement equals the marginal benefit for all units in the problem shed. This can be attained by price setting at the jurisdictional level or trade in credits. (vi) A major advantage of the CB approach is its well-defined relationship to weak sustainability. However, its value measures over-weight the preferences of the well-off. Equity considerations suggest relief from strict CB criteria in the case of essentials such as human health and nutrition, and subsidization by rich countries of sustainability projects in low-income countries. 

This article examines sustainability from a policy perspective rooted in environmental economics and environmental ethics. Endorsing the Brundtland Commission stance that each generation should have undiminished opportunity to meet its own needs, I emphasize the foundational status of the intergenerational commitment. The standard concepts of weak and strong sustainability, WS and SS, are sketched and critiqued simply and intuitively, along with the more recent concept of WS-plus. A recently proposed model of a society dependent on a renewable but vulnerable resource (Barfuss et al. 2018) is introduced as an expositional tool, as its authors intended, and used as a platform for thought experiments exploring the role of risk management tools in reducing the need for safety. Key conclusions include: (i) Safety, in this case, the elimination of risk in uncertain production systems, comes at an opportunity cost that is often non-trivial. (ii) Welfare shocks can be cushioned by savings and diversification, which are enhanced by scale. Scale increases with geographic area, diversity of production, organizational complexity, and openness to trade and human migration. (iii) Increasing scale enables enhancement of sustainable welfare via local and regional specialization, and the need for safety and its attendant opportunity costs is reduced. (iv) When generational welfare is stochastic, the intergenerational commitment should not be abandoned but may need to be adapted to uncertainty, e.g., by expecting less from hard-luck generations and correspondingly more from more fortunate ones. (v) Intergenerational commitments must be resolved in the context of intragenerational obligations to each other in the here and now, and compensation of those asked to make sacrifices for sustainability has both ethical and pragmatic virtue. (vi) Finally, the normative domains of sustainability and safety can be distinguished—sustainability always, but safety only when facing daunting threats.