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Evaluating Human Systems and Earth Systems – A Sustainability Model

I was reminded of a fascinating paper I read entitled ‘Modeling sustainability: Population, inequality, consumption, and bidirectional coupling of the earth and human systems.’

The graphic below from the paper shows the relationship of the human system within the earth system, not separate from it. The earth system provides the sources of the inputs to, and the sinks that absorb the outputs of, the human system.The key points are that:

  • The Human System is within the Earth System
  • The Earth System provides the sources of the inputs to Human System
  • The Human System outputs must be absorbed by the Earth System sinks.

Though the graphic below is busy, it’s a clear and intuitive model that makes sense.


What I found to be a more interesting perspective was the diagram that demonstrates the changes in the human impact on the planet over the years as outlined below. Once again, I think this makes intuitive sense.

This paper discusses an important concept for the scientific study of sustainability known as carrying capacity (CC). This is defined as the ‘total consumption—determined by population, in-equality, and per capita consumption—that the resources of a given environment can maintain over the long term. Consumption of natural resources by a population beyond the rate that nature can replenish overshoots the Carrying Capacity of a given system and runs the risk of collapse’. The ‘Modeling sustainability’ paper highlights, however, that:

Modern society has been able to grow far beyond Earth’s (carrying capacity) by using non-renewable resources such as fossil fuels and fossil water. However, results from the model show that an unsustainable scenario can be made sustainable by reducing per capita depletion rates, reducing inequality to decrease excessive consumption by the wealthiest, and reducing birth rates to stabilize the population. The key question is whether these changes can be made in time.
Current models of climate change include sea level rise, land degradation, regional changes in temperature and precipitation patterns, and some consequences for agriculture, but without modeling the feedback that these significant impacts would have on the Human System, such as geographic and economic displacement, forced migration, destruction of infrastructure, increased economic inequality, nutritional sustenance, fertility, mortality, conflicts, and spread of diseases or other human health consequences

One solution might be to construct reasonably integrated models that consider human systems and earth systems so we’re comparing apples to apples and not apples to coconuts.



I agree that one major issue is that the two disciplines of human systems and earth systems are conducted by different specialists using different systems and models and little has been done to integrate these. We need to get the right information, models and approaches to everyone to facilitate real-time, informed, and transparent decisions.



Safa Motesharrei, Jorge Rivas, Eugenia Kalnay, Ghassem R. Asrar, Antonio J. Busalacchi, Robert F. Cahalan, Mark A. Cane, Rita R. Colwell, Kuishuang Feng, Rachel S. Franklin, Klaus Hubacek, Fernando Miralles-Wilhelm, Takemasa Miyoshi, Matthias Ruth, Roald Sagdeev, Adel Shirmohammadi, Jagadish Shukla, Jelena Srebric, Victor M. Yakovenko, Ning Zeng; Modeling sustainability: population, inequality, consumption, and bidirectional coupling of the Earth and Human Systems, National Science Review, Volume 3, Issue 4, 1 December 2016, Pages 470–494,

Peter Milsom

Peter Milsom is an entrepreneurial advocate for sensible, sustainable change delivery practice. Peter has come to realize that sustainability is the perfect catalyst for Project / Programme / Portfolio / Risk / Value / Business Case and Benefits Management improvement. As an entrepreneurial methodologist Peter's unique value proposition is the vast array of tools and techniques that he brings to every engagement using the most cost effective and efficient methods based on the situation and tailored to meet your needs. This is based on his unique combination of experience and extensive training / certifications in change delivery, value / risk / benefits management business case, and business architecture.

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