In order to be useful for decision makers, scenarios must be plausible. They must also be integrated, coherent and internally consistent. Scenarios should be analytically sound with regard to use of data and scientific theory. Scenarios should not only incorporate the global scale but be able to be dis-aggregated to a regional and, ultimately, sub-regional scale.
Environmental management cannot consider environmental drivers in isolation from the socio-ecological system, and scenarios should reflect this. This makes scenario development more complicated and requiring a broader base of expertise to ensure that scenarios have an internally consistent set of assumptions about key relationships and driving forces from a social, economic and environmental point of view.
For scenarios to be defensible, they must also be transparent and well documented. This ensures:
- understanding of the reasoning behind and the assumptions made;
- informed criticism and further improvement by identifying any bias in scenario production and focusing subsequent argument on underlying uncertainties; and
- informing potential users of appropriate conditions under which scenarios might be used, not used or modified.
Despite the almost infinite range of possible futures that they could consider, scenarios should be limited in number. An even number of baseline scenarios is better than an uneven number, in order to prevent the decision-maker from settling for a “middle ground”. Four baseline scenarios are better than two, in order to avoid the decision-maker interpreting two scenarios as “extremes”. The appropriate use of scenarios refrains from “picking” any particular chain of events, but rather focuses on how a range of scenarios describes the most important uncertainties at stake.
Although limited in number, scenarios should also be diverse and represent a range of future visions, values and world-views. There are, in general, more policy than baseline scenarios, however; the number of policy scenarios must be kept manageable in order to avoid scenario fatigue.
It is also an advantage if scenarios can incorporate surprises, although this may be not be fully possible as baseline scenarios are ideally of limited number. Surprises can be positive or negative and include events such as a world war, “miracle” technologies, an extreme natural disaster, a pandemic or a breakdown of the climate system. The more plausible, yet unexpected, occurrences incorporated into scenario building exercises, the more decision makers will recognise the need for adaptive management.
Scenarios will also need to span long time horizons of at least several decades otherwise slow, incremental environmental change (whose full detrimental consequences will only be felt in a distant political future) have little leverage against high profile, short-term issues such as employment, crime rates and economic development.
Lastly, scenarios must have the ability to communicate options and outcomes clearly to a range of different stakeholders affected by them. The story line aspects of scenarios means that they can be used to communicate complex information to non-scientific audiences in an exciting and clear way. For instance, theatrical performances, film and video recordings have even been used to communicate plausible futures to audiences.