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Scenarios
are possible images of the future - neither predictions
nor forecasts; rather, they postulate how the future might
unfold. Scenarios are useful tools for scientific assessments,
for learning about the behavior of complex systems and
for policy making. Often they are formulated with the
help of numeric or analytic models. The scenarios generated
by the large-scale computer model used by the Club of
Rome in 1972 sparked global awareness of the importance
of sustainability.
When a system is well understood, it can be modeled with
relative certainty, but when physical or social systems
are poorly understood, or information on the relevant
variables is incomplete, such accurate prediction is not
possible. Scenarios are an appropriate tool for summarizing
both current understanding and current uncertainties.
For example, future levels of global greenhouse gas (GHG)
emissions are the products of a very complex, poorly-understood
dynamic system, driven by forces such as population growth,
socio-economic development, and technological progress.
Consequently, predicting future emissions accurately is
difficult. However, since near-term policies could have
profound long-term climate impacts, policy-makers want
to have some idea of the future of GHG emissions. GHG
emissions scenarios are usually based on a set of assumptions,
and formulated with the help of quantitative models.
Although no scenarios are value-free, it is often useful
to distinguish between normative and descriptive scenarios.
Normative scenarios are explicitly values-based, exploring
the routes to specific desired or undesired endpoints.
Descriptive scenarios are evolutionary and open-ended,
exploring paths into the future.
Good scenarios are challenging and may court controversy,
since not everybody is comfortable with the outcomes of
every scenario. When used intelligently, they allow policies
and strategies to be designed in a more robust way. They
represent an important tool in sustainable development,
since they offer policymakers a glimpse into the future
based on the activities of the present.
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