The Limits to Growth (LTG) is a 1972 report that examined how quickly the world’s economy and population could grow if Earth’s resources were limited. The study used a computer model called World3 to show how human activities and Earth’s systems might interact.

The report was created by the Club of Rome and first shared at international meetings in Moscow and Rio de Janeiro in 1971. The main authors were Donella H. Meadows, Dennis L. Meadows, Jørgen Randers, and William W. Behrens III, who worked with a team of 17 researchers. The World3 model was based on earlier work by Jay Forrester of MIT, as explained in his book World Dynamics.

The report’s findings stated that without major changes in how resources are used or how the environment is protected, the world could face a sudden and difficult drop in population and industrial production. Though the report was heavily criticized when it was released, it influenced environmental policies for many years. Later studies showed that the use of natural resources has not changed enough to prevent the outcomes predicted in the report. Predictions about rising resource prices also did not happen as expected.

Since its release, over 30 million copies of the book have been sold in 30 languages. The report continues to spark discussion and has led to other books. These include Beyond the Limits (1992) and The Limits to Growth: The 30-Year Update (2004). In 2012, Jørgen Randers, one of the original authors, published a 40-year forecast titled 2052: A Global Forecast for the Next Forty Years. In 2022, Dennis Meadows and Jørgen Randers, along with 19 other writers, released a new book called Limits and Beyond.

Purpose

The Club of Rome asked the MIT team to work on the project that led to LTG. They had three goals:

• To learn about the limits of our world system and how these limits affect the number of people and human activities.
• To find and examine the most important parts of the world system and how these parts work together to influence what happens over a long time.
• To warn about the possible results of current economic and industrial policies and encourage changes that support a lifestyle helpful for the environment and future.

Method

The World3 model is based on five factors: population, food production, industrialization, pollution, and the use of nonrenewable natural resources. At the time of the study, all these factors were increasing and were expected to continue growing very quickly. However, the ability of technology to increase resources was expected to grow only at a steady, slower rate. The authors wanted to explore how changing the growth patterns of these five factors might lead to a more sustainable balance. They explained that their predictions were only rough estimates of how the system might behave, not exact results. In two of the scenarios, the global system was expected to experience a period of rapid growth followed by a sudden decline by the middle to late 21st century. In the third scenario, the system was expected to reach a stable state.

A key idea in The Limits to Growth is that if the rate at which resources are used increases, the time until resources run out cannot be calculated by simply dividing the total known reserves by the current yearly usage. For example, in 1972, there were 775 million metric tons of chromium reserves, and 1.85 million metric tons were mined each year. Using the simple method, this would suggest chromium would last 418 years. However, the actual rate of chromium use was growing by 2.6% each year. If this growth rate is considered instead of a constant usage rate, the resource would last significantly less time.

The formula used to calculate the time remaining for a resource with increasing usage is:

The chapter includes a detailed table covering five pages, showing data on the reserves of 19 nonrenewable resources as of 1972. It analyzes how long these resources might last under three scenarios: static (constant usage), exponential growth, and exponential growth with reserves increased by five times to account for potential new discoveries. A small part of this table is shown in the text.

The chapter also includes a detailed computer model showing how chromium availability might change, using both the known reserves from 1972 and double that amount. It also discusses trends in the rising prices of various metals.

Because the model used real-world data and actual price trends, the numbers were often interpreted as predictions of when resources would run out. This interpretation was used by environmental groups to argue for conservation and by critics to question the accuracy of the model. This idea was widely shared by the media and environmental organizations, even though the book itself noted that the numbers were not meant to be taken as exact predictions.

Environmental groups used the model to support their arguments, while some economists criticized the book shortly after its release in the 1970s (e.g., Peter Passel, Marc Roberts, and Leonard Ross). Similar criticism was repeated in the 1990s by others, including Ronald Bailey and George Goodman. In 2011, Ugo Bardi wrote that the book never claimed the numbers were predictions. However, because these numbers were the only specific data related to resources, both supporters and critics used them as if they were predictions.

While Chapter 2 introduces the idea of modeling exponential growth, the actual World3 model uses an abstract concept of "nonrenewable resources" based on fixed values rather than specific physical materials.

Conclusions

After examining their computer simulations, the research team found these results:

— Limits to Growth, Introduction

The introduction also states:

Criticism

The Limits to Growth (LTG) study caused many different reactions, including strong criticism soon after it was published. In 1972, Peter Passell and two others wrote an article in the New York Times calling the LTG study "empty and misleading" and compared it to the old computer science idea: "Garbage In, Garbage Out." Passell believed the study's simulations were too simple and ignored the role of technology in solving problems like resource shortages, pollution, and food production. He argued that the LTG simulations always ended in collapse and predicted the end of valuable resources. Passell also claimed the study had a hidden goal: to stop economic growth.

In 1973, researchers at the Science Policy Research Unit at the University of Sussex said the LTG simulations were highly sensitive to a few key assumptions and that the assumptions used by the MIT team were overly pessimistic. The LTG team responded in a paper titled A Response to Sussex, pointing out five major disagreements. They argued that the Sussex critics used "small-scale reasoning for large-scale problems" and said their arguments were either misunderstood or misrepresented. The LTG team also noted that the critics did not suggest alternative models for how growth and resources interact or describe specific social or technological changes that could support growth.

At the time, many businesses and economists doubted the idea that global resources would run out, as the study suggested. Critics said history showed the LTG predictions were wrong, such as the claim that resources would be depleted and economies would collapse by the end of the 20th century. The study’s methods, computer models, conclusions, and the people involved were criticized. Yale economist Henry C. Wallich agreed that growth could not continue forever but believed a natural end to growth was better than forced intervention. He argued that technology could solve the problems the report addressed, but only if growth continued. Wallich warned that stopping growth too soon could harm billions of people.

Julian Simon, a professor at the Universities of Illinois and Maryland, said the LTG study’s basic ideas were wrong because the definition of a "resource" changes over time. For example, wood was once the main material for building ships, but concerns about shortages disappeared when boats were made of iron and later steel. Simon wrote in his book The Ultimate Resource that human creativity finds new resources from raw materials. He argued that copper will never "run out" because rising prices would lead to more discoveries, recycling, and better substitutes. His book was updated and republished in 1996 as The Ultimate Resource 2.

In 1973, Allen V. Kneese and Ronald Riker of Resources for the Future testified to the U.S. Congress, saying the LTG authors biased their models by allowing some factors to grow rapidly while limiting others. They noted that population, capital, and pollution grew exponentially in all models, but improvements in technology and pollution control were limited. However, their testimony also warned about long-term limits to carbon dioxide emissions and the risks of population growth in developing countries.

In 1997, Italian economist Giorgio Nebbia identified four main sources of criticism against the LTG study: businesses and industries threatened by the book’s ideas, economists who felt the study encroached on their field, the Catholic Church, which opposed the idea that overpopulation was a major problem, and the political left, which saw the study as a trick by elites to discourage workers. A UK government report noted that in the 1990s, critics often misunderstood the LTG study as predicting global resource depletion and collapse by the year 2000.

Peter Taylor and Frederick Buttle analyzed the LTG study and its system dynamics (SD) models. They found the original SD models were designed for businesses and influenced later models for cities and global systems. These early models relied on managers to control feedback loops caused by decisions made by different sectors. However, the later global model lacked such managers, leading to cycles of growth and collapse in most simulations. The model had only two solutions: changing the structure of population growth (a moral approach) or having a central authority direct changes (a technocratic approach). The LTG report combined both ideas. System dynamics models also simplified the world’s population and resources, making it harder to show how crises affect different regions differently. This lack of detail made the models less effective at reflecting real-world differences in politics, economics, and resource distribution.

Positive reviews

Economics has mostly focused on the idea that resources and pollution problems in one place can be moved to another, as if the world has no limits. When the report The Limits to Growth suggested that the world might have limits, many businesses and economists did not believe it. However, their rejection was based on incorrect assumptions.

In 1980, the Global 2000 Report to the President reached similar conclusions about future resource shortages and the need for countries to work together to prepare.

In a 2008 blog post, Ugo Bardi wrote that while The Limits to Growth (LTG) was often mocked in the 1990s, some people began to take its ideas seriously again. Matthew Simmons, who read LTG for the first time in 2000, later said that the report was correct in its predictions, and that people had ignored it for 30 years.

Robert Solow, who had criticized LTG earlier, said in 2009 that the situation had changed over 30 years and that it would be important to study how economic growth, resource availability, and environmental limits affect each other.

In 2008, Graham Turner from CSIRO found that real-world data from 1970 to 2000 closely matched the predictions from the LTG model. This match was within the expected range of uncertainty for most data. Turner also reviewed studies by economists that tried to dismiss LTG, finding that these studies had flaws and misunderstood the model.

In 2014, Turner wrote in The Guardian that data from the United Nations showed that population growth since 1972 matched the worst-case scenario in LTG. Birth and death rates were slightly lower than predicted, but these changes canceled each other out, leaving population growth nearly the same as the report had forecast.

In 2010, Nørgård, Peet, and Ragnarsdóttir called The Limits to Growth a "pioneering report" and said it had remained relevant over time.

In 2012, Christian Parenti compared the reception of LTG to how global warming has been treated. He noted that despite LTG’s scientific quality, powerful economic interests dismissed it. A similar situation is happening now with climate research.

In 2012, John Scales Avery, a member of the Nobel Prize-winning Pugwash Conferences, supported LTG’s main idea.

Legacy

The Club of Rome continued after the publication of Limits to Growth. They have updated the book every five years.

A review of past discussions about Limits to Growth in 1978 found that people were more hopeful, which slowed the environmental movement's progress. The article said that scientific arguments had a small role in people accepting different views.

In 1989, a meeting in Hanover was held with the title Beyond the Limits to Growth: Global Industrial Society, Vision or Nightmare?. In 1992, Beyond the Limits was published as a 20-year update to the original book. It said that 20 years of history mostly supported the original conclusions. The 1992 book also said that humanity had already used more resources than Earth can provide.

Limits to Growth: The 30-Year Update was published in 2004. The authors noted that people wasted the past 30 years on unproductive debates and weak responses to environmental challenges. They warned that without major changes, the world might face collapse during the 21st century.

In 2012, the Smithsonian Institution held a meeting called Perspectives on Limits to Growth. Another meeting that year, by the Volkswagen Foundation, was titled Already Beyond?.

Limits to Growth did not get an official update in 2012, but one of its coauthors, Jørgen Randers, wrote a book titled 2052: A Global Forecast for the Next Forty Years.

In 2008, physicist Graham Turner at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) published a paper titled A Comparison of 'The Limits to Growth' with Thirty Years of Reality. He compared 30 years of data with the book’s 11 scenarios and found that changes in industrial production, food production, and pollution matched the "business as usual" scenario. This scenario predicted economic and societal collapse in the 21st century. In 2010, researchers called the book a "pioneering report" and said its conclusions remain valid, though it was often dismissed as a "doomsday prophecy."

In 2008, researcher Peter A. Victor said the Limits to Growth team probably underestimated how prices affect outcomes, but critics overestimated this. He noted the book had a major impact on how people think about environmental issues and said the models were meant to be predictions only in a limited way.

In 2009, Hall and Day wrote in American Scientist that the model’s predictions and real-world data from 2008 were very close. This matched a 2008 CSIRO study, which said 30 years of data fit well with the book’s "standard run" scenario, which predicts global collapse by the middle of the 21st century.

In 2011, Ugo Bardi wrote a detailed study of Limits to Growth, its methods, and how it was received. He said the warnings from 1972 are becoming more concerning as real-world trends match the book’s predictions. A popular analysis by science writer Richard Heinberg also supported the report’s accuracy.

In 2012, Brian Hayes wrote in American Scientist that the model is more of a tool for argument than a scientific instrument. He said the graphs from the book’s computer program should not be used as predictions.

In 2014, Turner said preparing for a collapsing global system might be more important than trying to avoid it. A 2014 study from the University of Melbourne confirmed that real-world data closely matches the World3 BAU model from the book.

In 2015, researchers updated the World3-03 model using data from 1995 to 2012 to better understand today’s economic and resource systems. They found that society has invested more in reducing pollution, increasing food production, and improving service sectors, but the overall trends from Limits to Growth still hold.

In 2016, a group of UK lawmakers formed an all-party parliamentary group on Limits to Growth. Their report said society is still following the original study’s "standard run" scenario, where overuse of resources leads to eventual collapse. The report also noted that issues like climate change, not fully addressed in the 1972 book, add new challenges.

In 2020, Gaya Herrington, then Director of Sustainability Services at KPMG US, published a study in Yale University’s Journal of Industrial Ecology. The study examined updated data on 10 factors, including population, industrial output, and pollution, and concluded that the original predictions of Limits to Growth are correct. It said continued economic growth under a "business as usual" model is unsustainable, and growth could peak and decline by around 2040 if resource use does not change.

In 2023, the World3 model was updated using data up to 2022. This improved version shows the same pattern of overuse and collapse as the original Limits to Growth scenario. The update slightly raises the peaks of key variables and moves them a few years into the future.

Editions

• ISBN 0-87663-165-0 , 1972 first edition (digital version)
• ISBN 0-87663-222-3 , 1974 second edition (cloth)
• ISBN 0-87663-918-X , 1974 second edition (paperback)
• Meadows, Donella; Meadows, Dennis; Randers, Jorgen (1992). Beyond the Limits (Hardcover edition). Chelsea Green Publishing. ISBN 0-930031-55-5.
• Meadows, Donella; Randers, Jorgen; Meadows, Dennis (June 2004). Limits To Growth: The 30-Year Update (Paperback edition). Chelsea Green Publishing. ISBN 193149858X.
• Meadows, Donella; Randers, Jorgen; Meadows, Dennis (March 2005). Limits To Growth: The 30-Year Update (Hardcover edition). Chelsea Green Publishing. ISBN 1931498512.