Limits to Growth
This essay considers the 1972 book The Limits to Growth as a case in point when critiquing the ideology of exponential growth. The text, which used “world dynamics” models, alerted the world to the likelihood of collapse in both human and natural systems if exponential growth continued in population, industrial production, and exploitation of nonrenewable natural resources.
Background
As described by Ugo Bardi, cheap oil supported the growth of manufacturing, which had a growing middle class to consume its products;1 it fueled cars that made the urban sprawl possible; fueled the production of inexpensive fertilizers and farm equipment, which increased productivity and lowered the cost of food; and made the dramatic rise of plastics possible. The widespread availability of antibiotics and basic medical care, along with sufficient food, enabled the global human population to accelerate its exponential growth. At the same time, the overuse of renewable and nonrenewable resources was occurring at a localized scale. Advances in measurement technologies were enabling documentation of increasing trends of pollution in air, water, and soil.
As most of the West basked in this new prosperity, critical analyses of the consequences of these trends began emerging. Rachel Carson published Silent Spring in 1962;2 Garrett Hardin published his essay “The Tragedy of the Commons” in 1968,3 a year that also saw publication of The Population Bomb by Paul Ehrlich.4 In the spring of 1968 Dr. Aurelio Peccei, an industrial manager at Fiat and Olivetti and economist, gathered a group of thirty scientists, educators, economists, humanists, industrialists, and national and international civil servants for a meeting at the Accademia dei Lincei in Rome. The first meeting focused on “The Project on the Predicament of Mankind.”5 They decided that at the core of the “predicament of mankind” was the inability of humans to understand the sources, significance, and interrelationships of the components of society, which together were creating economic inequality, economic disruptions, insecure employment, and so on. Peccei met Jay Wright Forrester from the Massachusetts Institute of Technology (MIT), who was developing the new science of “industrial dynamics” or “system dynamics.” In 1970, Forrester convinced the Club of Rome to use system dynamics to explore the individual components and their interactions that comprised the global economic and environmental system. Forrester enlisted his former student and new faculty member at the time, Dennis Meadows, to undertake this task. The results of this effort were Forrester’s analysis World Dynamics, published in 1971, and The Limits to Growth, published in 1972 by Donella Meadows, Dennis Meadows, Jørgen Randers, and William W. Behrens III.6 Forrester sold about 100,000 copies and Meadows and his co-authors sold more than one million copies of the book, which was translated into over thirty languages. These analyses clearly resonated with growing concerns over coming world trends.
The World3 model
The World3 model was the system dynamics model developed by Meadows and co-workers to explore interrelationships between global systems. This model was one of the first large-scale system dynamics models made possible through a modern computing infrastructure. It represented the transition of computing methods used by the military to civil society and the critique of social trends. The model was the first to link the world economy with the global environment in an integrated fashion.
The World3 model is based on a “stock and flow” framework. The model tracks trends in five global subsystems: population, food production, industrial production, pollution, and consumption of nonrenewable natural resources. As the name implies, the geographic boundary of the model was the world and the temporal boundary was 1900 to 2011. As described by Turner (2007), the model involves four key elements. The first was feedback loops, both positive and negative. This enabled the propagation (positive) or dampening of modifications or trends within and between systems. The second element was an accounting of resources such as agricultural land, the productivity of which could be diminished by the functioning of the economic system (i.e. overuse). This is the essence of the “stock and flow” architecture of the model. The third element was the delay of signals between subsystems. For example, the model (correctly) delayed the impact of increasing pollution on reducing human life expectancy and agricultural production. This element, together with feedbacks, allowed the model to capture “overshoot” or the inability of the system to “correct” or stabilize itself before experiencing a downward trend (i.e. a decrease in food production and population). The fourth element was treating the world economic system as a set of complete subsystems. The importance of the interrelationships among these systems was a critical feature originally identified by the Club of Rome.
Due to the inherent complexity of each of the five subsystems, the World3 model necessarily simplified each system and hence the total global system. For example, industrial output and population were expressed as aggregate global values that neglected regional differences. Nonrenewable resources were defined as those resources that were essential for industrial production and with a regeneration time much longer than the 200-year time span of the model. Within each subsystem, a series of variables were used as inputs to the model. Data behind these variables were gleaned from world statistics. Outputs from the World3 model were eight variables including global population, crude birth rate, crude death rate, and services per capita.
The results from the World3 model were explosive. The model reproduced exponential rates of increasing population, per capita food availability, and industrial output from the early 1900s to the 1970s. The model forecast a bleak future, the crash of the global economy and of the human population, brought about primarily by resource constraints and secondarily by increasing pollution. In particular, the decline was produced by exponentially increasing global consumption of finite resources where increasing industrial output was required to obtain more scarce resources. In turn, the diversion of ever-increasing industrial output towards exploiting finite resources caused decreased investment in human welfare. Thus, the model drew a causal link between decreasing human welfare and resource consumption, a connection that hitherto had not been made so clearly. The results from the model also connected the diversion of industrial output to resource exploitation and away from agriculture, with the effect of reducing the per capita food supply.
In addition to producing a simulation of their “best estimate” of global trends, the model allowed for the testing of various hypotheses. For example, the model was used to test hypotheses within each submodel, such as the effect of desired family size on population growth. The effects of submodel interactions were also explored, such as the impact of unlimited resources on the output of the other submodels. The World3 model as a whole was used to explore the changes that would be required to stabilize the world population through technological advances that affected agricultural production, the availability of birth control, resource use, and pollution. As such, the World3 model allowed for a better understanding of the factors that could be useful to influence and stabilize world trends.
The Limits to Growth had a major impact. One reflection of that impact was the quick and fierce criticisms it received, to the extent of personal criticisms leveled at the modeling team. It provoked debate about the veracity of processes included in the model, which continues to be debated today. The critics were quick to point out that the analysis was yet another doomsday prognostication and could join others in the “dustbin of history,” such as Thomas Malthus’ prediction that population decline would be brought about by population growth and insufficient food. Others criticized the analysis for its inaccuracy—that projections contained in the analysis were not coming to fruition. But perhaps the key point is that the model fostered investigation and probing of the model and its components in a way that was not possible before it was published. It should also be borne in mind that this was the start of the science of systems analysis and simultaneous quantitative consideration of the economy and environment. Today, this represents a robust and fertile field of inquiry.
In 2007 and 2012, Graham Turner revisited the World3 model by updating model parameterization and evaluating model output against current data trends. The results of his analysis were disquieting. His analysis showed, in fact, that current data were consistent with trends predicted in the World3 model. Turner drew the connection between the economic downturn starting in 2008 and the diversion of industrial output towards extracting resources with a decreasing “energy returned on energy invested” or EROI. Thus, using the model, he pointed the finger directly at unfettered resource consumption as the underlying cause of the global economic downturn and that the downturn was prescient of global collapse.
As it had originally, The Limits to Growth’s more recent incarnations continue to provoke debate. It is a key argument used by proponents of sustainability. It has sparked inquiry into the underlying processes and the behaviors of the global economy as a whole. It enabled the “tame” consideration of the very wicked problem of the sustained future of the global population.
