Biophysical modeling of human and nature interactions, Human and 3-Nature Dynamics model (HAN3DY)

The increase in population, and per capita consumption, over the last century have caused an alarming increase in the use of natural resources, causing widespread concern on the sustainability of society. Since all biophysical quantities growing within a finite space would either, i) transition to an equilibrium position, ii) oscillate around an equilibrium state, or iii) overshoot and decline (Meadows, D, et.al, 1972), the Human and three-Nature Dynamics model (HAN3DY) attempts to investigate behavior modes between human and nature through thought experiments. This allows for the understanding of the dynamics of key components (capital, accumulated wealth, population, power, resources) with reference to key parameters (extraction rates, resource levels, etc.). The HAN3DY expands the capabilities of the HANDY model (Motesharrei, S. et.al, 2014) by introducing non-regenerative resources, renewable flow resources, capital, power, and the constant elasticity of substitution (CES) production form to address elasticity of substitution between input parameters in the extraction functions. While HAN3DY reveals that the ultimate cause of societal collapse is the high extraction rate of resources, it also reveals that non-regenerative resources help increase the growth rate of the population, while renewable flow resource acts as a complement to other sources of nature by increasing the carrying capacity of population.