IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group I: The Physical Science Basis Model Spectra or Hierarchies

The value of using a range of models (a ‘spectrum’ or ‘hierarchy’) of differing complexity is discussed in the TAR (Section 8.3), and here in Section 8.8. Computationally cheaper models such as EMICs allow a more thorough exploration of parameter space, and are simpler to analyse to gain understanding of particular model responses. Models of reduced complexity have been used more extensively in this report than in the TAR, and their evaluation is discussed in Section 8.8. Regional climate models can also be viewed as forming part of a climate modelling hierarchy.