The global future lies before us as a highly uncertain and contested landscape with numerous perils along the way. This study explores possible pathways to sustainability by considering in quantitative detail four contrasting scenarios for the twenty-first century. The analysis reveals vividly the risks of conventional development approaches and the real danger of socio-ecological descent. Nonetheless, the paper underscores that a Great Transition scenario—turning toward a civilization of enhanced human well-being and environmental resilience—remains an option, and identifies a suite of strategic and value changes for getting there. A fundamental shift in the development paradigm is found to be an urgent necessity for assuring a sustainable future and, as well, a hopeful opportunity for creating a world of enriched lives, human amity, and a healthy ecosphere.

Humanity confronts a daunting double challenge in the 21st century: meeting widely-held aspirations for equitable human development while preserving the bio-physical integrity of Earth systems. Extant scientific attempts to quantify futures that address these sustainability challenges are often not comprehensive across environmental and social drivers of global change, or rely on quantification methods that largely exclude deep social, cultural, economic, and technological shifts, leading to a constrained set of possibilities. In search of a broader set of trajectories, we combine three previously separate streams of inquiry: scenario analysis, planetary boundaries, and targets for human development. Our analysis indicates there are plausible, diverse scenarios that remain within Earth’s safe bio-physical operating space and achieve a variety of development targets. However, dramatic social and technological changes are required to avert the social-ecological risks of a conventional development trajectory. One identified narrative, which is predominant in the scenario literature, envisions marginal changes to the social and cultural drivers underlying conventional growth trajectories. As a result, it requires unprecedented levels of international cooperation, alignment of powerful conflicting interests, and political willpower to bend technological change in a sustainable direction. We posit that a more viable and robust scenario might lie in the coupling of transformative social-cultural and technological changes, which set the necessary conditions for a transition to a resilient global future. While clearly a first step, our analysis points to the need for more in-depth exploration of the mechanisms and determinant forces for such unconventional futures.

Global scenario assessments in support of climate, biodiversity, energy and other international policy deliberations tend to focus on a narrow bandwidth of possibilities: futures that unfold gradually from current patterns and trends. This “continuity bias” downplays the real risks (and opportunities) of structural discontinuity in the evolution of the global social-ecological system. The inclination to focus on mathematically tractable representations and conventional futures preferred by decision-makers is understandable, but constrains the scientific imagination and the scope of policy guidance. Earlier studies spotlighted discontinuous global futures, thereby revealing a broader spectrum of possibilities and repertoire of actions than found in contemporary scenario analysis. The paper revisits three types of futures introduced 25 years ago; examines three truths they convey about the contemporary moment; and points to three courses of action they suggest. Contemporary assessments centre on incrementally changing Conventional Worlds, yet varieties of global disruption (Barbarization) and progressive transformation (Great Transition) remain plausible alternatives. Corresponding to this triad, three synergistic action prongs—reform (incremental policies), remediation (emergency preparedness and prevention), and redesign (deep cultural and institutional change)—come into focus. Recovering a comprehensive perspective on the global possible would reinvigorate debate on the kind of transformation needed, broaden the action agenda, and stimulate innovative research for illuminating our indeterminate future. The COVID-19 pandemic, a concrete illustration of historical discontinuity, underscores the critical importance of emphasizing nonconventional futures in policy assessments.

Of all the environmental policy concepts to emerge in the last 20 years, none is more compelling than that of sustainability. The reason, of course, is the growing recognition that humanity is currently on an unsustainable path, that our activities have reached the point where they threaten the very life-support systems of the Earth. The need to preserve those systems was first put on the international policy agenda by the Brundtland Commission more than 10 years ago, which also formulated the classic definition of sustainable development, namely, development that “seeks to meet the needs and aspirations of the present without compromising the ability to meet those of the future.” The same goal has guided other international policy endeavors, notably the Earth Summit in 1992 and the recent climate negotiations in Kyoto.