Population Scenarios Based on Probabilistic Projections: An Application for the Millennium Ecosystem Assessment

Brian C. O'Neill, International Institute for Applied Systems Analysis (IIASA)

Probabilistic population forecasts offer a number of advantages to users. However, in some cases population is one component of a larger analysis that may take a different approach to uncertainty. For example, integrated assessments of environmental issues such as climate change or ecosystem degradation have typically used alternative scenarios to explore uncertainty in future environmental outcomes. In such cases, population projections that are provided only as probability distributions are difficult to use. I present a method of deriving individual, deterministic population projections that are consistent with scenarios for integrated assessments, but that are associated with quantitative uncertainty distributions, derived from fully probabilistic projections. I also describe an application of the method to the development of population projections for use in integrated scenarios for the Millennium Ecosystem Assessment, an international scientific effort to assess the current conditions of and future outlook for global ecosystem goods and services.