Table 1. Several major axes of variation characterize the diversity of purpose and approaches adopted in scenario exercises. The two columns represent the ends of a continuum. Most scenario exercises lie between these endpoints. Note that the different axes do not necessarily co-vary, i.e., the elements in each column need not co-occur. For example, an exploratory scenario could be motivated by either scientific inquiry or policy support (table adapted from Ducot and Lubben 1980, Bunn and Salo 1993, Wollenberg et al. 2000, van Notten et al. 2003).   Dimensions along which scenarios vary Range of variation Purpose Exploratory, investigate uncertainties and drivers of change ↔ Decision support, test robustness of policies Motivation Scientific inquiry ↔ Policy support Focus On process: development of storylines ↔ On outcome: implications of storylines for decision making Inclusion of norms Normative, e.g., scenarios reflect the desired and “good” or the undesired and “bad” ↔ Descriptive, not based on social preferences Approach Quantitative, “hard,” formal models: statistical forecasting, trend-impact analysis, cross-impact analysis ↔ Qualitative, “soft” methods: visioning, intuitive logic, storytelling Source of information Formal, rational, scientific observation ↔ Judgment and intuition of decision makers, intuitive, local knowledge systems and world views Level of uncertainty Low ↔ High Number of focal scales Single scale ↔ Multiple scales Links between scales Loosely linked: perspectives, uncertainties, and drivers from each scale partially inform scenario exercises at other scales ↔ Tightly coupled: perspectives, uncertainties, and drivers from each scale strongly inform the scenario exercises at other scales Number of storylines One ↔ Multiple (3–9, typically 3–5) Starting point of storyline Future, uses backward inference or “backcasting,” deductive ↔ Present, uses future inference, inductive, builds from knowledge of roles and environmental trends Endpoint of storyline “Snapshot” at one future point in time ↔ Story of events linked from present to future Driving forces Underlying (exogenous, external): hard or impossible to control by stakeholders ↔ Proximate (endogenous, internal): controllable to some extent by stakeholders Dynamics Simple ↔ Complex, includes thresholds and feedbacks Stakeholders as participants Active participants in construction and evaluation, i.e., participatory scenarios ↔ Passive objects of analysis, i.e., expert-driven scenarios Stakeholders as audience No communication strategy in mind ↔ Targeted communication strategy integral to design, e.g., policy briefings, drama, editorials