Languages:
A plausible and often simplified description of how the future may develop, based on a coherent and internally consistent set of assumptions about key driving forces (e.g., rate of technology change, prices) and relationships.
Scenarios are neither predictions nor projections and sometimes may be based on a “narrative storyline.”
Scenarios may include projections but are often based on additional information from other sources.
Source:
Millennium Ecosystem Assessment 
For scenarios on the world ecosystems, see the toolbox: scenarios of the Millennium Ecosystem Assessment
Español: Escenarios
Français: Scénario
Nederlands: Scenario
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