The quest for sustainable development is for the individual person largely conditioned by personal endowments and natural and social context. The mass of individual behaviours determines how the collective future unfolds, which in turn affects contexts. How such futures might unfold can be explored in a mix of qualitative story-telling and quantitative modelling, also known as scenarios. Many (world) futures scenarios have been constructed since one of the first ones, The Limits to Growth report (1971), was published. Their names reflect the underlying worldviews. The worldview framework can explicitly be used to link dominant values and beliefs to probable events and pathways, with the use of computer models. It should start with the narrative of Modernity and an investigation of counternarratives. It gives an impression of what humanity can expect in the coming century, and the potential overshoot-and-collapse risks. It can shape the agenda of sustainability science. In the end, however, it is primarily for the individual human being to (re)orient towards a more sustainable way of life and a corresponding state of consciousness and maturity.

If you have gone through some or all of the preceding chapters, you may be left with the feeling of what to do, who to be? Hopefully, the preceding texts also touch the heart, because, in Aristotle’s words, ‘educating the mind without educating the heart is no education at all’.

Minerals, notably metals and construction materials, have been used for millennia, but the extent and diversity has enormously increased with industrialization. They occur as deposits of chemically bonded elements, accumulated over geological time and non-renewable on a human scale. Unlike energy, materials accumulate in stocks of goods, buildings, machinery, etc., and waste. Material flow analysis (MFA) covers the entire chain of extraction, processing, manufacturing, (re-)using and dissipation. Problems arise with depletion of high-grade deposits and with pollution of the environment (mining, waste, etc.) and its impacts for human and ecosystem health. In particular, the production and use of existing and new persistent chemicals -- with plastics as the most visible example -- are a great and only partly understood threat. Parts of the flows are unrecoverably dissipated; this should be minimized by increasing efficiency, reducing losses and collecting and processing waste along the chain. Redesign, reuse and recycling and developing substitutes are other approaches to mitigate geopolitical tensions and environmental destruction. How successful this can and will be depends on worldviews and their relative dominance, for instance in continuing growth with corporate tech versus local--regional regulation and behavioural change.

In Part II, we discussed how human populations have dispersed throughout the biosphere and become a planetary force. In Part III, this was investigated with help of the worldview framework. This permits an interpretation of socio-ecological developments in terms of extreme manifestations of particular values and beliefs and the dynamic responses to it. Both science and ethics are important components in this venture.

The ’good life’ many people aspire to has many component. Three of them I call ’pillars of development’: health, education and mobility (HEM). Health has greatly improved for many people, due to a decline in mortality and morbidity rates. It shows up in the rise in life expectancy worldwide. This is primarily thanks to better food, hygiene and medical services. Because casues of mortality shifted from infectious diseases to chronic non-communicative degenerative ailments, the notion of health transition has been introduced. The level of formal education is also rising worlwide, with important consequences for political organization and rights for women. Mobility has experienced an enormous growth, which has resulted in ever larger distances travelled within an hour due to changes to faster modes (walk - bicycle - car/train/bus - plane). Many technological, economic and sociopolitical developments affect the future of HEM-infrastructure and services. All three have an inherent public-good character, which gives rise to divergent worldviews regarding their provision and quality (private versus state, efficiency versus availability).

In the next three chapters, I give an overview of how human populations evolved in various places and over time. The stories about ancient civilizations illustrate the socio-political, economic and environmental determinants of rise and decline. A variety of mechanisms and theories are proposed to ‘explain’ these processes (Chapter 3). By the end of the first millennium in the Common Era (CE), some populations on the continent of Europe began, over the course of half-a-dozen centuries, to get a prominent political-economic and military position in the world. It started the story of industrialization and enlightenment, two key aspects of what is known as Modernity. What did this mean in the ‘material’ sense: the numbers on people, economic activity, resource use, environmental destruction? (Chapter 4). Second, what did it mean for the less material aspects of life: the shifting balance between the institutions of state, church and market, the ‘progress’ brought by science and technology, and the concomitant changes in the perception of what is good and bad (Chapter 5)?

Water is essential for (human) life, as necessity and threat. With industrialization, water use has grown exponentially, notably in agriculture (irrigation). Withdrawal from open water and groundwater constitutes blue water use. Water in soils and vegetation is called green water; grey water refers to waste water flows. The complex stocks and flows of water can be related to human activity in the water footprint. Blue water use of surface and groundwater and its availability vary greatly across the globe. Many people live in water-stressed regions, due to groundwater depletion, little and/or irregular rain and declining quality due to pollution. Water is a prime example of a common pool resource (CPR), but increasing demand and subsequent scarcity have led to marketization and privatization of water provision and infrastructure.Because water use is intrinsically regional, water modelling and governance should be context-specific and participatory. The path to sustainable water use will have to address the divergent views on water as private or public good, and on ways to connect water engineering (including for hydropower) to practices less damaging for biodiversity (nature-based solutions).

Parts of Europe experienced from the seventeenth century a rapid growth in economic activity, in a combination of scientific discoveries and colonial conquest and exploitation. In a series of processes, some of them with medieval roots, populations and economic output (approximated in terms of monetary transactions) increased exponentially, first in Europe and its offshoots, then in the 20th century also elswhere. Humanity had entered the Anthropocene. Patterns of economic activity changed from agriculture to manufacturing, then to services. Trade connections multiplied in waves of globalization. Economic inequality within and between countries rose significantly during most of these centuries; it was greatly influenced by the rapid economic growth in China. The industrialization had great and harmful impacts on Nature, in the form of massive changes in landscapes and of pollution of air, water and soils. This is considered in detail in the chapters on food, water, energy and materials.

Industrialization and the concomitant growth in populations and economic activity happened in parallel with changes in everyday life, both material (hygiene, diet, mobility) and immaterial (literacy, law, values and ideas about political order and human life). It is associated with Enlightenment, the emancipatory stream of Modernity. It meant changing roles and relations between the major institutions: (nation-)state, church and (community-)market. The outstanding hallmark was and is the idea of Progress, exemplified in the characteristics of the scientific worldview and its claim to ’objective Truth’. Another feature lies in the new ideas about good and evil, as propounded in Industrial Era ethics of liberalism and utilitarianism and in Enlightenment ethics.

What is sustainable development about? Development means an unfolding of the individual and the collective along the dimensions of body, mind and spirit. Sustainability refers to the capability to uphold and develop a certain desired situation. Sustainable development can thus be interpreted as the wish and capability to preserve the quality of (human) life and its unfoldment, in harmony with other living beings and within the terrestrial constraints. It represents ideals and aspirations. Key aspects are the way in which the collective organizes their realization through institutions, and on the basis of which views of Nature and of needs.

The quest for sustainable development should build upon scientific knowledge - as the title of this book indicates. However, (scientific) knowledge is itself framed differently in different worldviews. The concept of complexity, and its increasing role in science, can assist in exploring some epistemological issues and approaches about the quality of (scientific) knowledge (post-normal and Mode-1 Mode-2 science, NUSAP) - important in times of ’alternative facts’. It also influences the scientific and engineering endeavour par excellence: (formal) modelling. In sustainability science, it shows up in intense efforts to complement natural science models with models that include (human) behaviour (next chapter). Communicating complexity happens also in less formal ways, with metamodels, analogues and metaphors, and organizing concepts (transition theory, social dilemmas and others).

The history of the concept of sustainable development shows early concerns on behalf of environmental NGOs and some religious people; later on, the voices of scientists, economists and businesses became (more) influential. The United Nations (UN) became a leading organizer and mediator. Gradually, the perception of the relationship between humans and Nature started to change, with important consequences for science and policy. The need for integrating the various aspects led to the emergence of Sustainability Science as a separate branch, and to the Sustainable Development Goals (SDGs) as an overarching framework for political actions and processes.