Box 4-1. Assessing the future: Projections and scenarios.

Recent international forward-looking assessments have made use of a variety of different approaches to explore key linkages between driving forces and assess resulting future develop­ments. The type of approaches employed range from forecasts, to projections, to exploring plausible scenarios. While these ap­proaches differ substantially, they have in common that they set out to assess possible future dynamics and understand related uncertainties and complexity in a structured manner (Figure 4-2).
     Projection-based studies commonly present one (or even several) probable outlook on future developments, which is often mainly based on quantitative modelling. Commonly, such pro­jections are based on reducing the level of uncertainty within a forward-looking assessment, either by addressing a limited time horizon or by focusing only on a subset of components of the socioeconomic and ecological system. Projections are particu­larly useful when they are compared against different variants to highlight expected outcomes of policy assumptions and well-defined options. Projections have also been referred to as future baselines, reference scenarios, business-as-usual scenarios, or best-guess scenarios, which usually hold many existing trends in driving forces constant.

     Conversely, forward-looking assessments based on more ex­ploratory approaches aim to widen the scope of discussion about future developments, or identify emerging issues. These types of assessments build on the analysis of alternative projections or scenarios that highlight a range of plausible future developments, based on quantitative and qualitative information. Such scenarios have been described as plausible descriptions of how the future may develop based on a coherent and internally consistent set of assumptions about key driving forces and relationships (MA, 2005a). Multiple projections or scenarios are most useful when strategic goals are discussed and reflected against a range of plausible futures, or when aiming to identify and explore emerging issues.

     Determining the forward-looking approach best suited to ad­dress a specific issue depends much on the level and type of uncertainty for which one needs to account. Uncertainties have a range of sources, including the level of understanding of the underlying causal relationships (i.e., "what is known about driving

B2 scenario (IPCC) or the Adapting Mosaic scenario (MA).
Business-as-usual scenarios: i.e., scenarios that build on the assumption of a continuation of past trends. Thus these scenarios are of a somewhat different quality than the archetypes presented above, as they are not constructed around key uncertainties. Instead business-as-usual scenarios might be described as projections. Examples of this type of scenario include the Refer­ence scenario (IFPRI) or the Agriculture Towards 2030 scenario (FAO).

forces and their impacts?"), the level of complexity of underpin­ning system's dynamics (i.e., "how do driving forces, impacts and their respective feedbacks determine future developments?"), the level of determinism of future developments (i.e., "to what de­gree do past trends and the current situation predetermine future developments?"), the level of uncertainty introduced by the time horizon (i.e., "how far into the future?"), or even surprises and unpredictable future developments (either because these fac­tors occur randomly or because existing knowledge is not able to explore them well enough) (for a discussion of different types of uncertainties and their consequences for methods to explore the future, see Van Vuuren, 2007). As a consequence, when as­sessments are faced only with relatively low levels of uncertainty with regard to future developments, some approaches allow predicting—or at least—projecting plausible future developments with some degree of confidence. Conversely, where the context of high uncertainty makes predictions or projections meaningless, exploratory scenario approaches can help explore possible de­velopments.

     Whereas different approaches to developing and analyzing projections and explorative scenarios exist, some common fea­tures have emerged in past assessments (see, for example, EEA, 2002). These include:

1.  Current state, i.e., a description of the initial situation of the respective system, including an understanding of past devel­opments that lead to the current state;
2.  Driving forces, i.e., an understanding of what the main actors and factors are, and how their choices influence the dynamics of their system environment;
3.  Step-wise changes, i.e., a description of how driving forces are assumed to develop and interact, and affect the state of a system along different future time steps;
4.  Image(s) of the future, i.e., a description of what a plausible future may look like as a consequence of assumptions on driv­ers, choices and their interactions;
5. Analysis, by looking across the scenarios to understand their implications and implied tradeoffs.

4.3 Indirect Drivers of Agricultural Change

4.3.1 Demographic drivers

4.3.1.1 Driving forces behind population projections
Past and future demographic trends, such as those for fer­tility levels, mortality levels and migration, are influenced by varied social, economical, environmental and cultural factors. The "demographic transition" (Thompson, 1929; Notestein, 1945) has proved to be a useful concept to de­scribe these trends in terms of several stages of transition.