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The Limits to Growth and World3

Abstract

On 2 March 1972 a team at MIT presented The Limits to Growth, a report for the Club of Rome built on World3, a computer model of the whole world economy from 1900 to 2100. Its method, system dynamics, had been invented by Jay Forrester, the builder of Whirlwind and core memory. Its message, that unchecked growth in population and industry would lead to collapse in the twenty-first century, sold millions of copies, helped launch the environmental movement, and made a computer simulation the centre of a political argument for the first time. Economists attacked it as “garbage in, garbage out”; later comparisons with real data found it closer to events than its critics expected.

From Whirlwind to System Dynamics

Jay Wright Forrester was born on 14 July 1918 in Climax, Nebraska, grew up on a cattle ranch, rode a mile and a half to school, and as a teenager built a wind-driven generator that brought his family electricity for the first time. He studied electrical engineering at the University of Nebraska and from 1939 worked on servomechanisms and feedback at MIT. From 1946 he led the construction of Whirlwind, MIT’s first electronic computer, which worked in real time and used the magnetic-core memory he invented; he then became chief designer of the computers for the SAGE air-defence system, which IBM built to his specifications (see Whirlwind, SAGE, and Core Memory).

In 1956 Forrester left computer building for the Sloan School of Management at MIT. There he developed system dynamics, a way of modelling companies, cities or whole societies as networks of stocks, flows and feedback loops, the control loops of his servo-laboratory days scaled up until only a computer could run them. He applied it with some success in industry and in city planning, set it out in three textbooks and a popular book, and called his larger simulations world models.

The Club of Rome

The Club of Rome, founded in 1968 by a group of managers, scientists, politicians and senior officials around Aurelio Peccei, head of Olivetti, wanted to study the shadow side of technical progress: war, disease, environmental destruction and overpopulation. At a meeting in Bern in June 1970 Peccei asked Forrester to compute the future of the world economy. On the flight home Forrester sketched a world model of boxes and arrows; at MIT he worked it out as World2, with five interacting variables: population, industrial output, food, non-renewable resources and pollution.

In the summer of 1970 Forrester set up a project team under Dennis Meadows, a 28-year-old management scientist, with sixteen researchers including Meadows’s wife Donella Meadows, a biophysicist, the Norwegian Jørgen Randers, William Behrens and three West Germans; the Volkswagen Foundation paid the budget of $250,000. The team extended World2 into World3 and ran several scenarios of industrialisation and resource use from 1970, computing population and its consequences for the planet over the years 1900 to 2100. The program was written in the simulation language DYNAMO and printed its curves on an ordinary line printer, time running down the paper and each variable plotted as a letter.

The Report

Dennis Meadows presented The Limits to Growth in Washington on 2 March 1972. The book, about two hundred pages, was written mainly by Donella Meadows. Its conclusion was stark: in almost every scenario the growth of population and industry overshot the Earth’s limits some time in the twenty-first century, followed by a rapid fall in food supply, industrial capacity and population. Only if population and per-capita output were held constant and resource use cut sharply did the model reach a stable equilibrium. The press summed the message up in one word: zero growth.

The book was translated into dozens of languages and sold in the millions (the HNF gives twelve million copies in 37 languages, Wikipedia thirty million in thirty). In 1973 the Club of Rome received the Peace Prize of the German Book Trade; the oil crisis that winter seemed to bear out its warning. It became a founding text of the environmental movement and in West Germany contributed to the rise of the Greens.

The Critics

The authority of the report rested partly on the computer, presented as neutral and all-knowing. Its critics went after exactly that. Peter Passell in the New York Times of 2 April 1972 called it “an empty and misleading work” and summed up the method as “garbage in, garbage out.” A group at the University of Sussex found in 1973 that the results were very sensitive to a few key assumptions and judged them unduly pessimistic; economists such as Julian Simon argued that the model ignored human ingenuity, which turns scarcity into substitution, and that technical progress grew only linearly in World3 while everything else grew exponentially.

Fifty Years On

The authors updated the work in Beyond the Limits (1992), which concluded that humanity had already overshot the Earth’s capacity, and in The Limits to Growth: The 30-Year Update (2004). In 2008 and 2014 Graham Turner of the Australian research agency CSIRO compared the standard “business as usual” run with real data from 1970 onwards and found a close match; in 2020 Gaya Herrington, working for KPMG, found current data broadly consistent with scenarios in which growth peaks and then declines around 2040.

Forrester received the IEEE Computer Pioneer Award in 1982 and the National Medal of Technology in 1989, and taught at MIT until his death in Concord, Massachusetts, on 16 November 2016.

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