Essays on Sustainability Science

Sustainability is a term that has gained prominence as a result of the consequences of the choices human society has made since the dawn of the Industrial Revolution. These choices have been resolving in an unprecedented increase in the capabilities of the human species, to the point that the consistency of its societal organization has come to rival the scale of all other dominions of the Earth (Turner et al. (1993); Vitousek et al. (1997); Harrison & Pearce (2000); Magalhães et al. (2016); Steffen et al. (2018); Rockström et al. (2024)). In this context, the term social-ecological system is defined as an all-encompassing, organicist perspective that integrates humanity and the natural environment into a single, interdependent whole (Ostrom (2009)). Was it a choice really? Was it a conscious choice? It has been pointed out that the way humans have organized their activities — what we call the economy — ultimately relies on life processes, just like everything else in the realms of biology and ecology (Daly (1968)). Sustainability asks if something can be sustained, that is continuing as is in the future. Sustainable Development is, on this regard, a compromise intent trying to reconcile the economy with the biological and abiotic elements, together making up the environment (World Commission on Environment and Development (1987); Goodland (1995); Du Pisani (2006); Brandt et al. (2013)). Wheater and how this could eventually be achieved is still both ontologically and epistemologically debated (Purvis et al. (2019)), constituting what Sustainability Science is all about (Sala et al. (2013)). This thesis is structured into three chapters focused on Sustainability Science: the first chapter presents an introductory essay, followed by two stand-alone papers. Chapter 1 — “The Sustainability Science research nexus: conceptual milestones” — presents a review of important conceptual milestones in Sustainability Science. It has not the pretence nor the possibility to be comprehensive, but it reports a few historical events and knowledge domains that is believed here being an overarching guide for the human society towards sustainability, as is in the eyes of the researchers proposing them. These conceptual milestones have certainly been the compass guiding my education and research throughout the years of the Ph.D. and, ultimately, to this thesis. The proliferation of the term sustainability and related concepts has been on the rise since the 1980s, sometimes so vaguely to lose any of its important meanings (Wu (2013)). An ontological and epistemological heterogeneity has been an underlying feature of the Sustainability Science research field as a whole since its inception (Purvis et al. (2019)). This is also why it has been decided not to overburden this introductory chapter with multiple variations of the same underlying concepts. It will become clear throughout the different sections that the ontological approach emerging from the cultural and scientific evolution of such milestones is that of an Earth system being increasingly considered as a single organism, a social-ecological system. The ontology underpinning the vision of the Earth system as a social-ecological system conceptualizes socioeconomic and ecological dimensions as a unified whole, such that the epistemological approach to research emerges from their integration. This is the driving insight of the two subsequent chapters. Chapter 2 — “Unveiling the temporal evolution of research themes in Sustainability Science through the Ecological Footprint concept: a bibliometric analysis for theoretical and methodological integration in systems of indicators” — presents a bibliometric analysis of the Ecological Footprint research field across the period 1992 - 2024, under a longitudinal framework. The Ecological Footprint is currently recognized as the only and most comprehensive metric accounting for the biological productivity required to sustain human economic activities (see, e.g., Galli, Wiedmann, et al. (2012); Fang et al. (2014); Charfeddine (2017);; Destek et al. (2018); Lin et al. (2018); Ozcan et al. (2018); Ahmed et al. (2019); Vanham et al. (2019); Danish et al. (2019); Xie et al. (2020); Ahmed et al. (2020); Ahmad et al. (2020)). Therefore, it has been chosen as the single keyword for bibliometric database search for it being an overarching concept for multiple interrelated instances in Sustainability Science. As such, it served as a passkey for retrieving bibliometric data that would have otherwise appeared more arbitrary and dispersed. Thematic networks are uncovered, coming from Sustainability Science as a whole, and their temporal evolution is presented together with performance indicators. In scientific research, specific topics in individual documents are represented by keywords. When connected through co-occurrence, these keywords form thematic networks that represent knowledge domains of interrelated concepts and reflect how research has been conducted in the past. Here, thematic networks are understood as higher-level structures that embody overarching scientific inquiries. They contribute to the literature by providing future researchers with sets of interdependent themes that highlight opportunities for integrating the diverse and interconnected dimensions of sustainability, which have so far been studied largely in isolation. This could possibly guide the harmonization and unification of current sustainability assessment methods — like the footprint family of indicators, and the planetary boundaries approach — with instances coming from the social and economic sciences as well, towards a unique framework. The geographical dimension of keywords is also defined and followed across time so to grasp geographical specificities and interdependencies of research themes across different studies, providing a more comprehensive picture for sustainability studies at the global level. This study provides key descriptive and performance analysis results as well, focusing on the spatial and temporal pattern of research interests across countries. All these results ultimately contribute to the comprehensive assessment and measurement of human society's sustainability in its spatiotemporal reality, an acknowledged necessity in both Ecological Footprint and Sustainability Science literature, yet one that remains insufficiently addressed (van den Bergh & Verbruggen (1999); Kates et al. (2001); Kates & Parris (2003); Rockström et al. (2009b); Kates (2011); Galli, Wiedmann, et al. (2012); Brandt et al. (2013); Wu (2013); Hoekstra & Wiedmann (2014); Fang et al. (2014); Sala et al. (2015); Steffen et al. (2015); Bennett et al. (2015); Folke et al. (2016); Vanham et al. (2019); Xie et al. (2020); Wu et al. (2021)). Chapter 3 — “The global dynamics of natural resources: an application of the predator-prey model to the National Ecological Footprint and Biocapacity Accounts” — delves more into the data provided by the Ecological Footprint methodology and theoretical framework across the period 1961 - 2020. Human activities compete for biologically productive space, resolving into a mounting depletion of natural resources and ecosystem services (Borucke et al. (2013); Lin et al. (2018)). Studies on the human-nature dynamics have long used biological and ecological analogies for modelling purposes. Indeed, this study follows the ontological and epistemological approach of the economy-as-an-organism foundational assumption of ecological economics (see Makriyannis (2022)). The Lotka — Volterra predator-prey dynamical system is applied to fit the Ecological Footprint time series data for countries aggregated at World Bank income level classification (World Bank (2022)), together with related variables that have been identified in previous literature as paramount for social-ecological resiliency. These are urban population and military expenditures (see, e.g., Kates & Parris (2003); York et al. (2003); Jorgenson (2005); Humphreys (2005); Jorgenson (2006); Dietz et al. (2007); Jorgenson & Burns (2007); Jorgenson & Clark (2009); Jorgenson & Clark (2011); Peng et al. (2018); Destek & Sarkodie (2019); Ahmed et al. (2020); Danish et al. (2020); Addai et al. (2022)). The analysis is then also portrayed at the UN region classification. The model parameters grasp the type of interaction between variables. Future projections up to 2100 are made. The implications of both are then discussed. This chapter contributes to the current literature by providing a new, initial, simple, and intuitive dynamical and time series empirical analysis of the Ecological Footprint and related data, by building two possible global social-ecological systems. It furthers the Ecological Footprint critical debate and results, and the more general stream of studies on the sustainability of current social-ecological systems within planetary boundaries and ecological intrinsic limits.