Models help to unlock latent tendencies in data, test our understanding of system structure and dynamics, and discuss policy issues in ways that expose assumptions and rules of inference. Models can use and/or generate data, but not all models do so. As used here, the term model refers to a quantitative description of all or part of the TERRA system. Models can be classified by form: i) computational models of varying complexity, completeness and fidelity to empirical data; empirical models to test specific hypotheses against real data and develop predictions from proven hypotheses; and theoretical models to derive useful conclusions from a set of starting assumptions and rules of inference. More broadly, TERRA models fall into three functional categories.

These types often overlap, as the following map of TERRA models shows:

An overview of TERRA’s broad range of modelling activities is provided below. In TERRA, models were used all along the ‘backbone’ shown on page 5. For hindsight, the main integrated model (IFs for TERRA) and the related indicator-based sustainable development model (ASA) provide comprehensive tools for exploring the past and the status quo. Of course, the empirical models, being estimated using historical data, provide summaries of past outcome and trends.

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