Climate models at different spatial scales and levels of
complexity provide the major source of information for
constructing scenarios. GCMs and a hierarchy of simple models
produce information at the global scale. These are discussed
further below and assessed in detail in Chapters 8 and 9. At the
regional scale there are several methods for obtaining sub-GCM
grid scale information. These are detailed in Chapter 10 and
summarised in Section 13.4. The most common method of developing
climate scenarios for quantitative impact assessments is to use
results from GCM experiments. GCMs are the most advanced tools
currently available for simulating the response of the global
climate system to changing atmospheric composition. All of the
earliest GCM-based scenarios developed for impact assessment in
the 1980s were based on equilibrium-response experiments (e.g.,
Emanuel et al., 1985; Rosenzweig, 1985; Gleick, 1986; Parry et
al., 1988). However, most of these scenarios contained no
explicit information about the tim