Global change and governance scholars frequently highlight polycentricity as a feature of resilient governance, but both theoretical and empirical knowledge about features and outcomes of the concept are lacking at the global scale. Here we investigate the structural properties of governance of global nitrogen (N) and phosphorus (P) cycles, two processes in the 'planetary boundaries' framework. We have used a mixed-methods approach to institutional analysis, integrating polycentric theory with social network theory in environmental policy and legal studies. We include an actor collaboration case study, the Global Partnership on Nutrient Management (GPNM), to explore governance challenges associated with global N and P cycles. We set the scope for selection of relevant legal instruments using an overview of global N and P flows between Earth system 'components' (land, water, atmosphere, oceans, biosphere) and the major anthropogenic N and P perturbations. Our network analysis of citations of global N and P governance exposes the structural patterns of a loose network among the principal institutions and actors, in which legal instruments of the European Union serve as key cross-scale and cross-sectoral 'gateways'. We show that the current international regimes in place for regulating N- and P-related issues represent a gap in governance at the global level. In addition, we are able to show that the emergence of GPNM provides synergies in this context of insufficient governance. The GPNM can be viewed as a structure of polycentric governance as it involves deliberate attempts for mutual adjustments and self-organised action.

Science is increasingly able to identify precautionary boundaries for critical Earth system processes, and the business world provides societies with important means for adaptive responses to global environmental risks. In turn, investors provide vital leverage on companies. Here, we report on our transdisciplinary science/business experience in applying the planetary boundaries framework (sensu Rockstrom et al., Ecol Soc 14, 2009) to define a boundary-compatible investment universe and analyse the environmental compatibility of companies. We translate the planetary boundaries into limits for resource use and emissions per unit of economic value creation, using indicators from the Carnegie Mellon University EIO-LCA database. The resulting precautionary 'economic intensities' can be compared with the current levels of companies' environmental impact. This necessarily involves simplifying assumptions, for which dialogue between biophysical science, corporate sustainability and investment perspectives is needed. The simplifications mean that our translation is transparent from both biophysical and financial viewpoints, and allow our approach to be responsive to future developments in scientific insights about planetary boundaries. Our approach enables both sub-industries and individual companies to be screened against the planetary boundaries. Our preliminary application of this screening to the entire background universe of all investable stock-listed companies gives a selectivity of two orders of magnitude for an investment universe of environmentally attractive stocks. We discuss implications for an expanded role of environmental change science in the development of thematic equity funds.

Coherently addressing the 17 Sustainable Development Goals requires planning tools that guide policy makers. Given the integrative nature of the SDGs, we believe that integrative modelling techniques are especially useful for this purpose. In this paper, we present and demonstrate the use of the new System Dynamics based iSDG family of models. We use a national model for Tanzania to analyse impacts of substantial investments in photovoltaic capacity. Our focus is on the impacts on three SDGs: SDG 3 on healthy lives and well-being, SDG 4 on education, and SDG 7 on energy. In our simulations, the investments in photovoltaics positively affect life expectancy, years of schooling and access to electricity. More importantly, the progress on these dimensions synergizes and leads to broader system-wide impacts. While this one national example illustrates the anticipated impact of an intervention in one specific area on several SDGs, the iSDG model can be used to support similar analyses for policies related to all the 17 SDGs, both individually and concurrently. We believe that integrated models such as the iSDG model can bring interlinks to the forefront and facilitate a shift to a discussion on development grounded in systems thinking.

Linking knowledge with action for effective societal responses to persistent problems of unsustainability requires transformed, more open knowledge systems. Drawing on a broad range of academic and practitioner experience, we outline a vision for the coordination and organization of knowledge systems that are better suited to the complex challenges of sustainability than the ones currently in place. This transformation includes inter alia: societal agenda setting, collective problem framing, a plurality of perspectives, integrative research processes, new norms for handling dissent and controversy, better treatment of uncertainty and of diversity of values, extended peer review, broader and more transparent metrics for evaluation, effective dialog processes, and stakeholder participation. We set out institutional and individual roadmaps for achieving this vision, calling for well-designed, properly resourced, longitudinal, international learning programs.

The Integrated History and future of People on Earth (IHOPE) initiative is a global network of researchers and research projects with its International Program Office (IPO) now based at the Stockholm Resilience Center (SRC), Uppsala University, Arizona State University, Portland State University, and the Australian National University. Research linked to IHOPE demonstrates that Earth system changes in the past have been strongly associated with changes in the coupled human-environment system. IHOPE supports integrating knowledge and resources from the biophysical and the social sciences and the humanities to address analytical and interpretive issues associated with coupled human-earth system dynamics. This integration of human history and Earth system history is a timely and important task. Until recently, however, there have been few attempts at such integration. IHOPE will create frameworks that can be used to help achieve this integration. The overarching goal is to produce a rich understanding of the relationships between environmental and human processes over the past millennia. HOPE recognizes that one major challenge for reaching this goal is developing 'workable' terminology that can be accepted by scholars of all disciplines. The specific objectives for IHOPE are to identify slow and rapidly moving features of complex social-ecological systems, on local to continental spatial scales, which induce resilience, stress, or collapse in linked systems of humans in nature. These objectives will be reached by exploring innovative ways of conducting interdisciplinary and transdisciplinary science, including theory, case studies, and integrated modeling. Examples of projects underway to implement this initiative are briefly discussed.

Humanity faces a major global challenge in achieving wellbeing for all, while simultaneously ensuring that the biophysical processes and ecosystem services that underpin wellbeing are exploited within scientifically informed boundaries of sustainability. We propose a framework for defining the safe and just operating space for humanity that integrates social wellbeing into the original planetary boundaries concept (Rockstrom et al., 2009a,b) for application at regional scales. We argue that such a framework can: (1) increase the policy impact of the boundaries concept as most governance takes place at the regional rather than planetary scale; (2) contribute to the understanding and dissemination of complexity thinking throughout governance and policy-making; (3) act as a powerful metaphor and communication tool for regional equity and sustainability. We demonstrate the approach in two rural Chinese localities where we define the safe and just operating space that lies between an environmental ceiling and a social foundation from analysis of time series drawn from monitored and palaeoecological data, and from social survey statistics respectively. Agricultural intensification has led to poverty reduction, though not eradicated it, but at the expense of environmental degradation. Currently, the environmental ceiling is exceeded for degraded water quality at both localities even though the least well-met social standards are for available piped water and sanitation. The conjunction of these social needs and environmental constraints around the issue of water access and quality illustrates the broader value of the safe and just operating space approach for sustainable development.

Background: The Planetary Boundaries concept (PBc) has emerged as a key global sustainability concept in international sustainable development arenas. Initially presented as an agenda for global sustainability research, it now shows potential for sustainability governance. Weuse the fact that it is widely cited in scientific literature (>3500 citations) and an extensively studied concept to analyse how it has been used and developed since its first publication. Design: From the literature that cites the PBc, we select those articles that have the terms 'planetary boundaries' or 'safe operating space' in either title, abstract or keywords. Weassume that this literature substantively engages with and develops the PBc. Results: Wefind that 6% of the citing literature engages with the concept. Within this fraction of the literature we distinguish commentaries-that discuss the context and challenges to implementing the PBc, articles that develop the core biogeophysical concept and articles that apply the concept by translating to sub-global scales and by adding a human component to it. Applied literature adds to the concept by explicitly including society through perspectives of impacts, needs, aspirations and behaviours. Discussion: Literature applying the concept does not yet include the more complex, diverse, cultural and behavioural facet of humanity that is implied in commentary literature. Wesuggest there is need for a positive framing of sustainability goals-as a Safe Operating Space rather than boundaries. Key scientific challenges include distinguishing generalised from context-specific knowledge, clarifying which processes are generalizable and which are scalable, and explicitly applying complex systems' knowledge in the application and development of the PBc. We envisage that opportunities to address these challenges will arise when more human social dimensions are integrated, as we learn to feed the global sustainability vision with a plurality of bottom-up realisations of sustainability.

The planetary boundaries framework proposes quantitative global limits to the anthropogenic perturbation of crucial Earth system processes, and thus marks out a planetary safe operating space for human activities. Yet, decisions regarding resource use and emissions are mostly made at less aggregated scales, by national and sub-national governments, businesses, and other local actors. To operationalize the planetary boundaries concept, the boundaries need to be translated into and aligned with targets that are relevant at these decision-making scales. In this paper, we develop a framework that addresses the biophysical, socio-economic, and ethical dimensions of bridging across scales, to provide a consistently applicable approach for translating the planetary boundaries into national-level fair shares of Earth's safe operating space. We discuss our findings in the context of previous studies and their implications for future analyses and, policymaking. In this way, we link the planetary boundaries framework to widely-applied operational and policy concepts for more robust strong sustainability decision-making.

Atmospheric organic nitrogen (ON) appears to be a ubiquitous but poorly understood component of the atmospheric nitrogen deposition flux. Here, we focus on the ON components that dominate deposition and do not consider reactive atmospheric gases containing ON such as peroxyacyl nitrates that are important in atmospheric nitrogen transport, but are probably not particularly important in deposition. We first review the approaches to the analysis and characterization of atmospheric ON. We then briefly summarize the available data on the concentrations of ON in both aerosols and rainwater from around the world, and the limited information available on its chemical characterization. This evidence clearly shows that atmospheric aerosol and rainwater ON is a complex mixture of material from multiple sources. This synthesis of available information is then used to try and identify some of the important sources of this material, in particular, if it is of predominantly natural or anthropogenic origin. Finally, we suggest that the flux of ON is about 25 per cent of the total nitrogen deposition flux.

The potential consequences of cross-scale systemic environmental risks with global effects are increasing. We argue that current descriptions of globally connected systemic risk poorly capture the role of human-environment interactions. This creates a bias towards solutions that ignore the new realities of the Anthropocene. We develop an integrated concept of what we denote Anthropocene risk-that is, risks that: emerge from human-driven processes; interact with global social-ecological connectivity; and exhibit complex, cross-scale relationships. To illustrate this, we use four cases: moisture recycling teleconnections, aquaculture and stranded assets, biome migration in the Sahel, and sea-level rise and megacities. We discuss the implications of Anthropocene risk across several research frontiers, particularly in the context of supranational power, environmental and social externalities and possible future Anthropocene risk governance. We conclude that decision makers must navigate this new epoch with new tools, and that Anthropocene risk contributes conceptual guidance towards a more sustainable and just future.

Changes to climate-carbon cycle feedbacks may significantly affect the Earth system's response to greenhouse gas emissions. These feedbacks are usually analysed from numerical output of complex and arguably opaque Earth system models. Here, we construct a stylised global climate-carbon cycle model, test its output against comprehensive Earth system models, and investigate the strengths of its climate-carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon cycle feedbacks and the operation of the carbon cycle. Specific results include that different feedback formalisms measure fundamentally the same climate-carbon cycle processes; temperature dependence of the solubility pump, biological pump, and CO2 solubility all contribute approximately equally to the ocean climate-carbon feedback; and concentration-carbon feedbacks may be more sensitive to future climate change than climate-carbon feedbacks. Simple models such as that developed here also provide workbenches for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the planetary boundaries, that are currently too uncertain to be included in comprehensive Earth system models.

The idea that there is an identifiable set of boundaries, beyond which anthropogenic change will put the Earth system outside a safe operating space for humanity, is attracting interest in the scientific community and gaining support in the environmental policy world. Rockstrom et al. (2009) identify nine such boundaries and highlight biodiversity loss as being the single boundary where current rates of extinction put the Earth system furthest outside the safe operating space. Here we review the evidence to support a boundary based on extinction rates and identify weaknesses with this metric and its bearing on humanity's needs. While changes to biodiversity are of undisputed importance, we show that both extinction rate and species richness are weak metrics for this purpose, and they do not scale well from local to regional or global levels. We develop alternative approaches to determine biodiversity loss boundaries and extend our analysis to consider large-scale responses in the Earth system that could affect its suitability for complex human societies which in turn are mediated by the biosphere. We suggest three facets of biodiversity on which a boundary could be based: the genetic library of life; functional type diversity; and biome condition and extent. For each of these we explore the science needed to indicate how it might be measured and how changes would affect human societies. In addition to these three facets, we show how biodiversity's role in supporting a safe operating space for humanity may lie primarily in its interactions with other boundaries, suggesting an immediate area of focus for scientists and policymakers.

Extreme weather events, such as the UK floods of 2007 and cold snap of 2010-2011, stress the importance of infrastructure systems' resilience for business continuity. The interconnected nature of critical national infrastructure and its component parts places demands on the approach used to deal with its subsequent complexity. Recognition of infrastructure as a complex adaptive system has led to the development of an innovative, systems-based methodology for sustainability assessment in the built environment. The methodology consists of a database of causal interactions which, when combined with a process, allows users to produce causal loop diagrams that identify unanticipated systemic behaviour, communicate risks, share knowledge, and identify systemic intervention points that minimise negative consequences and add value in a project context. The approach is applied to highlight the key characteristics of complex adaptive systems that critical national infrastructure exhibits and show how the technique can be used to increase infrastructure resilience and sustainability.

A transition to a decentralised, decarbonised energy system for the domestic sector is constrained by the difficulty of obtaining energy balance between fluctuating demand and the intermittent, non-dispatchable power supply delivered by most renewables. A microgrid system including a mix of renewable generation technologies, energy storage and demand response (DR) systems has been modelled using a linear programming approach, based on real world data of residential energy consumption and weather variables. This model allows the exploration of the effects of fluctuations in demand and supply, microgrid scale and configuration, energy management options and alternative optimisation criteria. The model demonstrates quantitatively that a mixed-renewables microgrid system can reduce demand fluctuations and improve energy balance. Peak demand hour fluctuations were reduced by up to 19% for a simulated microgrid containing 144 households with one renewable unit and four batteries per household, with a renewables mix of 83% photovoltaic (PV) panels and 17% wind turbines. With this system, the demand on macrogrid energy supply was reduced by 16%, CO2 emissions associated with energy use were reduced by 10% for all hours of operation, and by 74% during the hours of renewable supply. These findings suggest that microgrids using contemporary technologies can contribute significantly to CO2 mitigation targets.

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries-climate change and biosphere integrity-have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a Hothouse Earth pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.

There is a need for more integrated research on sustainable development and global environmental change. In this paper, we focus on the planetary boundaries framework to provide a systematic categorization of key research questions in relation to avoiding severe global environmental degradation. The four categories of key questions are those that relate to (1) the underlying processes and selection of key indicators for planetary boundaries, (2) understanding the impacts of environmental pressure and connections between different types of impacts, (3) better understanding of different response strategies to avoid further degradation, and (4) the available instruments to implement such strategies. Clearly, different categories of scientific disciplines and associated model types exist that can accommodate answering these questions. We identify the strength and weaknesses of different research areas in relation to the question categories, focusing specifically on different types of models. We discuss that more interdisciplinary research is need to increase our understanding by better linking human drivers and social and biophysical impacts. This requires better collaboration between relevant disciplines (associated with the model types), either by exchanging information or by fully linking or integrating them. As fully integrated models can become too complex, the appropriate type of model (the racehorse) should be applied for answering the target research question (the race course).

The exponential increase in the use of plastic in modern society and the inadequate management of the resulting waste have led to its accumulation in the marine environment. There is increasing evidence of numerous mechanisms by which marine plastic pollution is causing effects across successive levels of biological organization. This will unavoidably impact ecological communities and ecosystem functions. A remaining question to be answered is if the concentration of plastic in the ocean, today or in the future, will reach levels above a critical threshold leading to global effects in vital Earth-system processes, thus granting the consideration of marine plastic pollution as a key component of the planetary boundary threat associated with chemical pollutants. Possible answers to this question are explored by reviewing and evaluating existing knowledge of the effects of plastic pollution in marine ecosystems and the 'core planetary boundaries', biosphere integrity and climate change. The irreversibility and global ubiquity of marine plastic pollution mean that two essential conditions for a planetary boundary threat are already met. The Earth system consequences of plastic pollution are still uncertain, but pathways and mechanisms for thresholds and global systemic change are identified. Irrespective of the recognition of plastic as a novel entity in the planetary boundaries framework, it is certain that marine plastic pollution is closely intertwined with global processes to a point that deserves careful management and prevention.

We discuss the role of expert modelling in sustainability using a framework designed to improve the effectiveness of the modelling process. Based on the development of a set of reflective questions that can be used at certain key stages in the lifecycle of projects developing such models, we discuss how using the framework would lead to improvements in the coupling of the process of expert modelling with the process of intervention, which is implied by the existence of the expert modelling project. This questioning pushes the development of a framework beyond considerations of ontology and epistemology into issues of axiology and praxis; extending the notion of contested modelling beyond the narrow scientific sense to a wider social setting. Our framework has been developed through a case study analysis of the effectiveness of four research initiatives that have used expert modelling to address the complexity of intervention in a sustainability context.