Integrated assessment is definedhere as any attempt to integrate information from and acrossdisciplines to help in the process of developing policy responses(Parson, 1994). Assessment is distinguished from disciplinary researchby its purpose: to inform policy and decision, rather than to advanceknowledge for its intrinsic value. Integrated assessment is identifiedby the breadth of knowledge sources on which it draws; it is to bedistinguishes from those (infrequent) instances in which a significantpolicy issues can be well informed by a clear presentation of a body ofknowledge held within a single discipline. Distinguishing integratedassessment from other assessment is important because integratedassessment poses distinct and difficult challenges.
The broader the set of knowledge domains that must be synthesized toinform a policy or decision, the greater the intellectual andmanagerial problems that must be overcome to do the assessment well andmake it useful to its audience. How integrated any particularassessment must be depends on the issue or the decision to be informed.Perhaps more than any other policy issue, global climate changerequires integrated assessment. Making rational, informed socialdecisions on climate change potentially requires knowledge of the humanactivities that affect greenhouse gas emissions; the atmospheric,oceanic, and biological processes that link emissions to atmosphericconcentrations; the climatic and radiative processes that linkatmospheric concentrations to global and regional climate; theecological, economic, and socio-political processes by which suchevaluations are made. Any progress in understanding, and responding to,an issue of such complexity will require the capacity to integrate,reconcile, organize, and communicate knowledge across domains – thatis, to do integrated assessment. This need has been widely recognized,in calls to advance methods of integrated assessment, and in the largenumber of projects now underway. While there have been past examples ofintegrated assessments of major environmental issues (e.g. the AmericanCIAP Project, Grobecker et al 1974, and the European acid rain studiesintegrated in the RAINS model, Alcamo et al 1990), the current level ofintegrated assessment activity on global climate change isunprecedented.