Taxonomies for structuring World–Earth models

The paper starts from the observation that Earth system models have left social processes outside the model, and that in the Anthropocene this blocks understanding of Earth resilience and of how to govern global environmental change. The modelling landscape is wide and mixed, from purely biophysical Earth system models to macro-economic integrated assessment models to many models of socio-cultural dynamics, and models that simulate entangled human and Earth processes together do not yet exist. Building them means selecting and combining components from several modelling traditions, which needs a structured way to identify, classify and critique those components.

The proposal is a set of taxonomies. Modelled subsystems fall into three taxa: biophysical, whose dynamics are usually written as laws of physics, chemistry or ecology; socio-cultural, dominated by human behaviour, decision-making and collective dynamics such as politics, institutions and social networks; and socio-metabolic, the material interactions between the two, such as human bodies, natural resources and agriculture. Higher-order taxonomies then classify the interactions between two or more subsystems, which lets the authors point at the social–ecological feedback loops where new modelling work is needed. The sections of the paper walk every pairing: environment to environment, environment to metabolism, culture to environment, and so on.

As a worked example the taxonomy is applied to a stylised World–Earth model in which the discount rate in a greenhouse-gas emissions game is transmitted socially, to show the effect of feedback loops that current models leave out.

For a builder the paper is a vocabulary for saying which parts of a place a model covers and which it has externalised, and a checklist of the couplings a whole-system twin would have to carry. Volume 12, pages 1115 to 1137; DOI 10.5194/esd-12-1115-2021.