A system dynamics model of social, economic, and environmental earth systems and their interdependencies.

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Felix © Poornima Kumar

The Full of Economic-Environment Linkages and Integration dX/dt (FeliX) model represents a feedback-rich system dynamics perspective on the social, economic, and environmental sub-components of the Earth system.

Critical interdependencies are represented to capture the core physical and anthropogenic mechanisms of global environmental and economic change.

The aggregate model can be adapted and simulated easily and quickly to explore the long-term implications of human-earth system feedbacks in the context of climate change mitigation and sustainable development.

About FeliX

Through 12 core modules, FeliX simulates complex interactions within and between 10 global systems: population, education, economy, energy, water, land, food (including diet change), carbon cycle, climate, and biodiversity. The model outcomes are determined by many interacting feedback loops within and between these systems, as shown in the figure below.

Felix Overview © Moallemi et al. (2022).

Overview of the FeliX model. Modified based on the figure in Moallemi et al. (2022).

The model is calibrated to historical data available from the FAO, IEA, IRENA, the World Bank, UN Population Division and Wittgenstein Center for Demography and Global Human Capital. FeliX is a time-continuous simulation model across the time horizon 1900- 2100. The period 1900-2025 is the calibration period, varying across the model variables dependent on data availability, and the projection period is 2025-2100. FeliX scenario outcomes project on a global scale major stock changes (e.g., depletion of natural resources, accumulation of carbon dioxide in the atmosphere) as well as the aggregate consequences of policies and technologies (e.g., afforestation, emissions reduction) over time.

The first version of the model was developed by Felicjan Rydzak and Michael Obersteiner. Between 2014 and 2017, FeliX model maintenance and development has been led by Brian Walsh. Currently, the model maintenance and development is undertaken by Sibel Eker in various projects including CHOICE and WorldTrans to improve the representation of social systems and behaviour changes in integrated assessment modelling. As of 2025, a regional version (FeliX-R5) has been developed by Quanliang Ye based on the five United Nations’ regional classifications. This intends to facilitate fine-scale analysis of socioeconomic-environmental dynamics that take geographic, socioeconomic and cultural differences into account.

 

FAST FACTS

  • The baseline scenario in FeliX maps to benchmark RCP and SSP2 outcomes, allowing for robust conclusions regarding the relative impact of a wide array of policies and technologies.
  • FeliX reveals important synergies and tradeoffs between developmental and environmental goals, hence enables comprehensive assessment of sustainable development goals (SDGs). 
  • Expected demand for food, feed, and fiber is at the heart of the model, giving insight into trends in land use change as well as the allocation of other resources in the absence of environmental interventions.
  • Complex linkages among model sectors reveal indirect, potentially unintended, consequences of both targeted and general interventions.
  • FeliX enables exploring the implications of population heterogeneity and societal change for low-carbon lifestyles.
  • An online simulator, FeliXSim, allows the model to be accessible and interactive for non-experts, supporting engagement and participatory scenario development.

Addressing Knowledge Gaps

One of the key knowledge gaps about the potential of demand-side mitigation, as identified in the most recent IPCC report, is how widespread behaviour and lifestyle changes occur as a result of the dynamic interaction of individual, social, economic and environmental factors. FeliX is one of the few models that have the ability to represent these interactions, for example–in the dietary module, dietary shifts and food demand are a result of the endogenous population dynamics of dietary choices. This feature is based on the key theories of behaviour change from environmental psychology, and captures the role of psychological and social factors such as climate risk perception and social norms, in addition to the socioeconomic drivers such as income and education level, as described in detail by Eker et al. (2019).

Another unique feature of FeliX is to capture the interactions between a large number of sustainable development goals and their indicators so that the potential for their simultaneous achievement, synergies and tradeoffs can be analyzed, as exemplified by Moallemi et al. (2022) and Liu et al. (2023)   

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Yang, J., Gao, L., Guo, Z., Dong, Y., Moallemi, E.A., Eker, S. , Liu, Q., Chi, Z., Liu, F., Obersteiner, M. , & Bryan, B.A. (2025). Integrative Sustainable Development Goal policy portfolios to accelerate global progress towards a more sustainable future: a modelling study. The Lancet Planetary Health 9 (12) e101318. 10.1016/j.lanplh.2025.101318.

Eker, S. , Reiter, C. , Liu, Q., Kuhn, M., & Lutz, W. (2026). Wellbeing cost of carbon. Global Sustainability 9 e1. 10.1017/sus.2025.10042.

Lutz, W. & Pachauri, S. (2023). Systems Analysis for Sustainable Wellbeing. 50 years of IIASA research, 40 years after the Brundtland Commission, contributing to the post-2030 Global Agenda. IIASA Report. Laxenburg, Austria: International Institute for Applied Systems Analysis (IIASA) 10.5281/zenodo.8214208.

Liu, Q., Gao, L., Guo, Z., Dong, Y., Moallemi, E.A., Eker, S. , Yang, J., Obersteiner, M. , & Bryan, B.A. (2023). Robust strategies to end global poverty and reduce environmental pressures. One Earth 6 (4) 392-408. 10.1016/j.oneear.2023.03.007.

Moallemi, E.A., Eker, S. , Gao, L., Hadjikakou, M., Liu, Q., Kwakkel, J., Reed, P.M., Obersteiner, M., Guo, Z., & Bryan, B.A. (2022). Early systems change necessary for catalyzing long-term sustainability in a post-2030 agenda. One Earth 5 (7) 792-811. 10.1016/j.oneear.2022.06.003.

Eker, S. , Reese, G., & Obersteiner, M. (2019). Modelling the drivers of a widespread shift to sustainable diets. Nature Sustainability 10.1038/s41893-019-0331-1.

Walsh, B. , Ciais, P., Janssens, I.A., Penuelas, J., Riahi, K. , Rydzak, F., van Vuuren, D.P., & Obersteiner, M. (2017). Pathways for balancing CO2 emissions and sinks. Nature Communications 8 e14856. 10.1038/ncomms14856.

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