An equivalent database to document narrative and other qualitative scenarios would also be very useful for future climate-change assessments. One difficulty encountered in the analysis of the emissions scenarios is that the distinction between climate policy scenarios, non-climate policy scenarios, and other scenarios appeared to be to a degree arbitrary and was often impossible to make. Therefore, the writing team recommends that an effort should be made in the future to develop an appropriate emissions scenario classification scheme. The sources of inherent uncertainties range from data and modeling uncertainties through to inadequate scientific understanding of the underlying problems. Scenarios are appropriate tools for dealing with such uncertainty.
Scenarios are images of the future, or alternative futures.
Scenarios are not predictions. The SRES approach involved the development of a set of four alternative scenario families that encompass the 40 scenarios. Each family of SRES scenarios includes a descriptive part called a storyline, and a number of alternative interpretations and quantifications of each storyline developed by six different modeling approaches. Each storyline describes a demographic, social, economic, technological, and policy future for one of these scenario families. Within each family different scenarios explore variations of global and regional developments and their implications for GHG and sulfur emissions.