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0.3 Existing Elements

Each environmental assessment project carried out by PBL does not start with a blank slate. Furthermore, many analyses are iterative, building on earlier work, rather than wholly novel. In every case, there is some set of existing resources and experience that can be brought to bear. In addition, the guidance tool does not build from scratch either. There is by now a large body of uncertainty typologies, methodologies, and uncertainty assessment processes. A suitable selection has been made for use in the guidance. A summary of some of these existing elements follows.

In the process of carrying out environmental assessments at PBL a common set of tasks tends to be encountered. These tasks include monitoring studies (emissions, concentrations), model-based and data-based assessments, indicator choices, scenario development and analysis, policy analysis and evaluation. A body of experience has already been developed in carrying out these various tasks. Further, each task tends to have characteristic methods that are used in fulfilling the task. In turn, these methods have their own characteristic uncertainties associated with them.

Uncertainty types
The uncertainties characteristic of particular problems or methods should be organized in a form suitable for analysis. The organization of uncertainty types that is used in the guidance is described in the typology in section 1.4 and in appendix A. Different uncertainties have different properties, and a suite of uncertainty assessment methods have been developed to address them (see van der Sluijs et al., 2003).

Uncertainty tools
A range of methods exist to address both quantitative and qualitative aspects of uncertainty. Examples of such methods are sensitivity analyses, NUSAP, PRIMA, and checklist approaches. Many of these methods have been drawn together in an uncertainty assessment tool catalogue (see van der Sluijs et al., 2003).

A focus on uncertainty tools alone is inadequate for capturing many of the qualitative dimensions of uncertainty. For this purpose a number of process-based approaches have also been developed. This set includes extension of peer communities, incorporation of stakeholders into the assessment process, problem framing from multiple perspectives, education, and communication.