HANDY Model for Civilisational Collapse Scenarios

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= the Human and nature dynamics (HANDY) models inequality and use of resources in the collapse or sustainability of societies


• HANDY is a 4-variable thought-experiment model for interaction of humans and nature. The focus is on predicting long-term behavior rather than short-term forecasting.

• Carrying Capacity is developed as a practical measure for forecasting collapses.

• A sustainable steady state is shown to be possible in different types of societies. But over-exploitation of either Labor or Nature results in a societal collapse.



* Article: Human and nature dynamics (HANDY): Modeling inequality and use of resources in the collapse or sustainability of societies. By Safa Motesharrei, Jorge Rivas and Eugenia Kalnay. Ecological Economics Volume 101, May 2014, Pages 90-102

URL = http://www.sciencedirect.com/science/article/pii/S0921800914000615

Abstract: "There are widespread concerns that current trends in resource-use are unsustainable, but possibilities of overshoot/collapse remain controversial. Collapses have occurred frequently in history, often followed by centuries of economic, intellectual, and population decline. Many different natural and social phenomena have been invoked to explain specific collapses, but a general explanation remains elusive.

In this paper, we build a human population dynamics model by adding accumulated wealth and economic inequality to a predator–prey model of humans and nature. The model structure, and simulated scenarios that offer significant implications, are explained. Four equations describe the evolution of Elites, Commoners, Nature, and Wealth. The model shows Economic Stratification or Ecological Strain can independently lead to collapse, in agreement with the historical record.

The measure “Carrying Capacity” is developed and its estimation is shown to be a practical means for early detection of a collapse. Mechanisms leading to two types of collapses are discussed. The new dynamics of this model can also reproduce the irreversible collapses found in history. Collapse can be avoided, and population can reach a steady state at maximum carrying capacity if the rate of depletion of nature is reduced to a sustainable level and if resources are distributed equitably."


"From the Collapses of even advanced civilizations have occurred many times in the past five thousand years, and they were frequently followed by centuries of population and cultural decline and economic regression. Although many different causes have been offered to explain individual collapses, it is still necessary to develop a more general explanation. In this paper we attempt to build a simple mathematical model to explore the essential dynamics of interaction between population and natural resources. It allows for the two features that seem to appear across societies that have collapsed: the stretching of resources due to strain placed on the ecological carrying capacity, and the division of society into Elites (rich) and Commoners (poor).

The Human And Nature DYnamical model (HANDY) was inspired by the predator and prey model, with the human population acting as the predator and nature being the prey. When small, Nature grows exponentially with a regeneration coefficient γ, but it saturates at a maximum value λ. As a result, the maximum regeneration of nature takes place at λ / 2, not at the saturation level λ. The Commoners produce wealth at a per capita depletion rate δ, and the depletion is also proportional to the amount of nature available. This production is saved as accumulated wealth, which is used by the Elites to pay the Commoners a subsistence salary, s, and pay themselves κs, where κ is the inequality coefficient. The populations of Elites and Commoners grow with a birth rate β and die with a death rate α which remains at a healthy low level when there is enough accumulated food (wealth). However, when the population increases and the wealth declines, the death rate increases up to a famine level, leading to population decline.

We show how the carrying capacity – the population that can be indefinitely supported by a given environment (Catton, 1980) – can be defined within HANDY, as the population whose total consumption is at a level that equals what nature can regenerate. Since the regrowth of Nature is maximum when y = λ / 2, we can find the optimal level of depletion (production) per capita, δ* in an egalitarian society where xE ≡ 0, δ∗∗(≥ δ∗) in an equitable society where κ ≡ 1, and δ*** in an unequal society where xE ≥ 0 and κ > 1.

In sum, the results of our experiments, discussed in Section 6, indicate that either one of the two features apparent in historical societal collapses – over-exploitation of natural resources and strong economic stratification – can independently result in a complete collapse. Given economic stratification, collapse is very difficult to avoid and requires major policy changes, including major reductions in inequality and population growth rates. Even in the absence of economic stratification, collapse can still occur if depletion per capita is too high. However, collapse can be avoided and population can reach equilibrium if the per capita rate of depletion of nature is reduced to a sustainable level, and if resources are distributed in a reasonably equitable fashion."


Nafeez Ahmed:

"Anthropologist and complex society expert, Prof Adam T. Smith of Cornell University, said that the HANDY model's central thesis - that a collapse of industrial civilisation due to unsustainable resource exploitation and increasing economic inequality - is perfectly plausible:

"The archaeological record is quite unambiguous: every prior society in every part of the world has ultimately been eclipsed. Human communities are kinds of machines – machines for social life – and just like any machine they fall apart and are discarded. However, civilisational collapse is actually quite rare.

Civilisational collapse typically involves the disappearance of entire ways of life, systems of thought, cultural values and worldviews. These generally do not disappear due to convulsive periods of collapse but rather fade over time as alternative systems of belief take their place.

However, although civilisational collapse is rare, political collapse is constant. Kingdoms, principalities, republics and states come and go and typically their downfall is violent and convulsive. The warnings in the recent study should carry significant warnings to current global political leaders: address the threats posed by climate change and economic inequality or face the rapid undoing of the current political order. The archaeological record suggests that while civilization will likely endure, politics as we know it, odds are, will not." (https://www.theguardian.com/environment/earth-insight/2014/mar/21/climate-change-scienceofclimatechange)

Why the HANDY model is so useful

Nafeez Ahmed:


"Dr Rodrigo Castro of the Department of Environmental Systems Science at ETH Zurich, Switzerland, delivered earlier this month, explains in detail why the HANDY model is so useful:

"It is our predicament that we live in a finite world, and yet we behave as if it were infinite. Steady exponential material growth with no limits on resource consumption and population is the dominant conceptual model used by today's decision makers. This is an approximation of reality that is no longer accurate and started to break down. The World3 model, originally developed in the 1970s [aka the 'Limits to Growth' project which despite Kloor's dismissals has turned out quite accurate according to American Scientist], includes many rather detailed aspects of human society and its interaction with a resource limited planet. However, World3 is a rather complex model. Therefore it is valuable for pedagogical reasons to show how similar behavior can be also realized with models that are much simpler. This paper presents a series of world models, starting with very simple exponential growth and predator-prey systems, then investigates a minimal human-nature model, Handy, and ends with a brief account of the World3 model. For the first time, a simple human-nature interaction model is made available in Modelica that distinguishes between dynamics of Elite and Commoner social groups. It is shown that Handy can reproduce rather complex behavior with a very simple model structure, as compared to that of world models like World3.


An interesting feature of Handy is that it introduces the accumulation of economic wealth, and divides the human population into rich and poor according to their unequal access to available wealth...

Social inequality is not only explicitly considered but also plays a key role in the sustainability analyses of the model. This makes Handy the first model of its kind that studies the impacts of inequality on the fate of societies, a capability seldom found even in complex world models.

Handy establishes a useful general framework that allows carrying out 'thought experiments' about societal collapse scenarios and the changes that might avoid them.

The model is a very strong simplification of the human-nature system, which results in many limitations. Despite its simplicity, such a model is easy to understand and offers a more intuitive grasp of underlying dynamical phenomena compared to more complex and less aggregated models.


"Although models presented in this paper are from different classes (minimal Handy vs. more complex, realistic world model, World3), their conclusions are similar. In the long run, not so far into the future, humanity must change to living sustainably on planet Earth. This change can occur either as a planned gradual transition, preserving well-functioning societies, or as a more disruptive, unplanned transition resulting in a less pleasant society with a reduced ecological capacity."" (https://www.theguardian.com/environment/earth-insight/2014/mar/21/climate-change-scienceofclimatechange)


"According to Dr. Deborah S. Rogers of Stanford University's Institute for Research in the Social Sciences, who is a leading expert in modelling inequality and social stratification:

"Models do not prove hypotheses, nor do they replicate reality. Rather, models are useful because they give us some insight into possible mechanisms and possible consequences. These new insights, then, feed into the iterative process of hypothesis-testing that underlies good science.

There is no problem with models that are 'simplistic' – they are supposed to be. A model is an abstraction from – a simplification of – reality. The objective is to see if you can understand the essential mechanism(s) that drive the system, and what some possible consequences of this mechanism might be. If the model results give you valuable insights into certain real-world trends, then maybe you have managed to capture the essence of the mechanism. If not, then you probably haven't, and you will need to either revise your model or add components to it.

There is no particular value to making a model complex...you add just enough complexity until you are convinced that you have captured the essence of the mechanisms you are trying to understand. Meanwhile, it is fully acknowledged that there are many other things also going on in reality, that are not captured by the model...

Likewise, a demography/resources model that predicts collapse given certain relationships between the population and their resource base does not need to include the complexities of political, economic and social adjustments made in response to the situation. It merely shows us the possible outcomes, and leaves it to the archaeologists, anthropologists, social scientists, political scientists, economists, and policy-makers to debate the actual and hypothetical responses to these possibilities, and how they altered (or will alter) the outcomes...

The HANDY model finds that unequal populations collapse, although they apparently attribute this to the lack of labor as the working class dies off. Again, without commenting on the adequacy of the specifics of the HANDY formulation, I find the simplicity of the model useful and the results plausible. If we want to criticize the HANDY model, and by the same token our Spread of Inequality model, let’s focus on the specific mechanisms that are postulated – not on the simplicity of the model, and not on the lack of exact parallels with past events." (http://www.nafeezahmed.com/2014/03/the-nasa-collapse-study-controversy.html)


  • Article: Human and Nature Dynamics (HANDY): Modeling inequality and use of resources in the collapse or sustainability of societies. By Safa Motesharrei, Jorge Rivas, and Eugenia Kalnay. Ecological Economics

Volume 101, May 2014, Pages 90-102

URL = https://www.sciencedirect.com/science/article/pii/S0921800914000615

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