[This section and the next section contain text drawn from Paul Raskin (30 June 2000; 1 September 2000 (revised); 16 October 16 2000 (second revision)) and GEO-3 Scenarios: Preliminary Framework' (SEI-Boston).]
AMCEN's mandate to assess long-range environmental issues poses significant methodological challenges. Because the time horizon expands from years to decades, the long-range future cannot be extrapolated or predicted due to three types of indeterminacy: ignorance, surprise and volition. First, insufficient information on both the current state of the system and on the forces governing its dynamics leads to a classical statistical dispersion over possible future scenarios. Second, even if precise information were available, complex systems are known to exhibit turbulent behaviour, extreme sensitivity to initial conditions and branching behaviours at various thresholds. Therefore, the possibilities for novelty, surprise and emergent phenomena make prediction impossible. Finally, the future is unknowable because it is subject to human choices that have not yet been made. In the face of such indeterminacy, scenarios offer a means for examining the forces shaping the world, the uncertainties that lie ahead and the implications for tomorrow of today's actions.
A scenario is a story, told in words and numbers, concerning the manner in which future events could unfold, and offering lessons on how to direct the flow of events towards sustainable pathways and away from unsustainable ones. Development scenarios are alternative stories about the future with a logical plot and narrative. Scenarios usually include images of the future-snapshots of the major features of interest at various points in time-and an account of the flow of events leading to such future conditions.
Scenarios draw both on science-on our understanding of historical patterns, current conditions, and physical and social processes-and on the imagination in order to conceive, articulate and evaluate alternative pathways of development and the environment. In so doing, scenarios can illuminate the links between issues, the relationship between global and regional development, and the role of human actions in shaping the future. It is this added insight-leading to more informed and rational action-that is the foremost goal of scenarios, rather than prediction of the future.
Figure 4.2: Scenario dynamics
Ruskin, P.D. and Kemp-Benedict, E. (2002)
Although scenarios certainly can offer quantitative insight, they are not primarily modelling exercises. The qualitative scenario narrative plays a critical role in giving voice to key aspects such as cultural influences, values, behaviours and institutions, which are not quantifiable. Thus, scenarios can provide a broader perspective than model-based analyses, while at the same time making use of various quantitative tools, such as accounting frameworks and mathematical simulation models. Quantitative analysis offers a degree of structure, discipline and rigour. Scenarios can offer texture, richness and insight.
Figure 4.2 illustrates the major features that govern the dynamics of change associated with scenarios of combined human and environmental systems. The 'current state' of the system is the outcome of an historical process, which is driven forward by a set of 'driving forces'. Moreover, the capacity of human beings to imagine alternative futures and to act intentionally means that images of the future can act as 'attractive forces' and 'repulsive forces' in shaping a scenario. In addition, there is the possibility that surprising and extreme occurrences-called 'sideswipes'-could affect development. Many unexpected events could be involved (for example, a breakdown of the climate system, a world war, cheap fusion power, a major natural disaster or a rampant global epidemic such as HIV/AIDS), but probabilities cannot be assigned, nor can all the possibilities be imagined.
Some key issues to consider in the formulation of scenarios include: the boundary; the current state; the definition and determination of driving forces; the narrative, or storyline; and images of the future.