A sensitivity analysis of the Earth for all model: Getting the giant leap scenario with fewer policies

Abstract

Integrated assessment models (IAMs) are popular tools used to predict the evolution of human society, a challenging question that science has long tried to address. The World3 model is a popular IAM, designed in the seventies by several scientists convened by the Club of Rome and mostly known for its usage to analyze the so-called limits to growth. The recent Earth for all (E4A) model has been initiated by one of the major co-authors of the World3 model, Jørgen Randers. It is substantially more complicated than the relatively simple World3 model, and it has been used to compare two different and opposite world development scenarios: the too little too late scenario, in which current policies are assumed to continue, and the giant leap (GL) scenario, in which 21 policies related to five turnarounds are identified to produce significant improvements in six indicators of human well-being. By using global and local sensitivity analyses of the E4A model, we suggest that the evolution of the six indicators in the GL scenario can be approximately reached by focusing on just six policies and three turnarounds (namely, the energy, the inequality, and the poverty turnarounds). The evolution of the six indicators can be even improved by investing “reasonably” more on three of these six policies and by keeping unchanged the remaining three. From a methodological point of view, we exploit both global (Sobol) and local sensitivity analyses to identify the policies that most influence the six indicators, and we subsequently execute a scenario analysis of the identified policies to confirm that they can produce a similar (or even a better) evolution of the indicators themselves.