Modeling Sustainability: Population, Inequality, Consumption, and Bidirectional Coupling of the Earth and Human Systems.

The authors highlight the following (direct from article):

1. The Human System has become strongly dominant within the Earth System in many different ways.

• Consumption, inequality, and population have increased extremely fast, especially since ∼1950.
• The collective impact of these changes threatens to overwhelm the viability of natural systems and the many critical functions that the Earth System provides.

2. Changes in the Earth System, in turn, have important feedback effects on the Human System, with costly and serious consequences.
3. However, current models, such as the Integrated Assessment Models (IAMs), that explore the future of humanity and environment, and guide policy, do not incorporate these critical feedbacks.

• Key Human System variables, such as demographics, inequality, economic growth, and migration, are instead driven by exogenous projections, such as the UN population tables.
• Furthermore, such projections are shown to be unreliable.

4. Unless models incorporate such two-way couplings, they are likely to miss important dynamics in the real Earth–Human system that may result in unexpected outcomes requiring very different policy interventions.
5. Therefore, Earth System Models (ESMs) must be bidirectionally coupled with Human System Models.

• Critical challenges to sustainability call for a strong collaboration of both earth and social scientists to develop coupled Earth–Human System models for devising effective science-based policies and measures.
• We suggest using Dynamic Modeling, Input–Output (IO) models, and Data Assimilation to build and calibrate such coupled models.

Abstract

Over the last two centuries, the impact of the Human System has grown dramatically, becoming strongly dominant within the Earth System in many different ways. Consumption, inequality, and population have increased extremely fast, especially since about 1950, threatening to overwhelm the many critical functions and ecosystems of the Earth System. Changes in the Earth System, in turn, have important feedback effects on the Human System, with costly and potentially serious consequences. However, current models do not incorporate these critical feedbacks. We argue that in order to understand the dynamics of either system, Earth System Models must be coupled with Human System Models through bidirectional couplings representing the positive, negative, and delayed feedbacks that exist in the real systems. In particular, key Human System variables, such as demographics, inequality, economic growth, and migration, are not coupled with the Earth System but are instead driven by exogenous estimates, such as United Nations population projections. This makes current models likely to miss important feedbacks in the real Earth–Human system, especially those that may result in unexpected or counterintuitive outcomes, and thus requiring different policy interventions from current models. The importance and imminence of sustainability challenges, the dominant role of the Human System in the Earth System, and the essential roles the Earth System plays for the Human System, all call for collaboration of natural scientists, social scientists, and engineers in multidisciplinary research and modeling to develop coupled Earth–Human system models for devising effective science-based policies and measures to benefit current and future generations.

Reference

Motesharrei, S., Rivas, J., Kalnay, E., Asrar, G. R., Busalacchi, A. J., Cahalan, R. F., ... & Hubacek, K. (2016). Modeling Sustainability: Population, Inequality, Consumption, and Bidirectional Coupling of the Earth and Human Systems. National Science Review, nww081.

You can find the article here (open access). Science Daily has also covered the work.