.SystemDynamics.WorldDynamics.World3.Scenario_4

Information

This is Scenario #4 of the WORLD3 model. This scenario starts out with the same assumptions as Scenario #3. Improvements in pollution control technology have led to an increase in the population. There are additional mouths to be fed, but unfortunately, not enough food is being grown to feed the population in the long run. The population stagnates, and there is massive hunger in the world.

In this new scenario, it is thus postulated that additional efforts are being undertaken to increase the yield of food per hectare of arable land.

References:

  1. Meadows, D.H., D.L. Meadows, J. Randers, and W.W. Behrens III (1972), Limits to Growth: A Report for the Club of Rome's Project on the Predicament of Mankind, Universe Books, New York, 205p.
  2. Meadows, D.L., W.W. Behrens III, D.M., Meadows, R.F. Naill, J. Randers, and E.K.O. Zahn (1974), Dynamics of Growth in a Finite World, Wright-Allen Press, 637p.
  3. Meadows, D.H., D.L. Meadows, and J. Randers (1992), Beyond the Limits, Chelsea Green, 300p.
  4. Meadows, D.H., J. Randers, and D.L. Meadows (2004), Limits to Growth: The 30-Year Update, Chelsea Green, 368p.

In order to accomplish this change, you need to modify the table P_Yield_Tech_Chg_Mlt_LYCM that models a multiplier to the investment in technology to improve land yield:

parameter Real p_yield_tech_chg_mlt[:] = {0,0,0.04,0.04} "Yield technology change multiplier";.

Simulate the model from 1900 until 2100, and display the same variables as in the book Limits to Growth: The 30-Year Update at page 215:

The results obtained are visibly different from those shown in the book Limits to Growth: The 30-Year Update primarily due to the quantization error.

In this model, some of the gains are huge. For example, the variable agr_inp_per_hect, i.e., the investment in agricultural production per hectare of arable land, that in earlier scenarios assumed values in the range [2,30] dollars per hectare and year suddenly assumes values of several thousands of dollars per hectare and year. We observe hyperinflation at work.

Due to the amplified quantization errors, the collapse happens more than 20 years earlier than shown in the book. If we were to simulate beyond the year 2100, the results obtained using the Modelica implementation could be considered similar to those obtained using STELLA. The trajectories simply get shifted in time. However, since we stop the simulation in 2100, our results look qualitatively different.

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