Thursday, 08 October 2009 12:29 Approaching The Ultimate Limits
Written by Emmett Duffy

ltg.jpgAs an academic ecologist researching or teaching about ecosystems, a common dilemma is the issue of how to define the boundaries of a system. Where, for example, does the Chesapeake Bay end and the Atlantic begin? What is the edge of the Hubbard Brook ecosystem? Et cetera. But there is one major exception to this rule: planet earth. We can define the edges of that superecosystem reasonably well. For all practical purposes we are limited, as a global society, to the resources we have here, with the single major exception of incoming solar radiation.

Humans have now grown in abundance and influence to the point where we are the force of nature. Which begs the ultimate practical question about ecosystems: How is humanity interacting with the planetary ecosystem, and is this suite of interactions sustainable?

Obviously, this generation is not the first to ask these questions. In 1972, a team lead by Donella Meadows from MIT published a book called “The Limits to Growth” (LTG), which presented results of a computer modeling study commissioned by a think-tank, The Club of Rome, concerned about the mounting impacts of unsustainable human activities on the earth system. They examined the interactions of five subsystems of the global economic system: population, food production, industrial production, pollution, and consumption of non-renewable natural resources. The model began in 1900 and continued to 2100. The model was able to reproduce broadly the historical data to the year 1970.


ltgpredictions.jpgThe central message from the LTG model  was that growth of the global economy would lead to exceeding planetary limits sometime in the 21st century, likely resulting in collapse of the human population and economic system.

BUT, the model also suggested, collapse could by an aggressive program of changes in behavior, progressive policy, and strategic application of technology.

LtG modeled three scenarios:

1) The “standard run” represents a business-as-usual situation where physical, economic, and social relationships were maintained more or les as they were during 1900–1970. This run (see the figure above) shows continuing economic growth into the early decades of the 21st century but signs of increasing environmental pressure at the start of the 21st century (e.g., resources diminishing, pollution increasing exponentially, growth slowing in food, services, and material wealth per capita). Sounds uncomfortably familiar? Finally, this scenario resulted in “overshoot and collapse” of the global system in mid-21st century due to diminishing resources and increasing pollution.

2) The “comprehensive technology” approach—approximating suggestions of “optimists” like Julian Simon or Bjorn Lomborg—attempts to solve sustainability issues with purely technological solutions. This scenario assumes (as do some economists, astonishingly enough) that levels of resources are effectively unlimited, as well as efficient recycling of materials, big reductions in pollution, doubling of agricultural land yields, and availability of birth control world-wide. Hmm. This scenario delayed the collapse of the global system to the latter part of the 21st century, after which economic growth outstripped the gains in efficiency and pollution control.

turner1.jpg3) The “stabilized world” scenario assumed implementation of both technological solutions and deliberate social policies to reach equilibrium in population, material wealth, food, and services per capita. Policies implemented include perfect birth control for a family size of two kids per couple; preference for consumption of services over material goods; effective control of pollution; maintenance of agricultural land; and increased lifetime of industrial capital, among others.

The publication of the Limits to Growth study (LtG) in 1972 had immediate and ongoing impacts. Millions of copies were sold, and it was translated into 30 languages. It linked the world economy with the environment in the first integrated global model.

Needless to say, the book was also highly controversial. There was and remains a sustained campaign to discredit the LtG, including repeated misrepresentations that the LtG predicted resources would be depleted and the world system would collapse by the end of the 20th century. So people have been arguing about this for more than 30 years.

Surprisingly, no one thought to test whether the predictions were true until very recently, when Graham Turner published a paper comparing historical data for 1970–2000 with the LtG scenarios. Here’s what he found (see the other figures here):

turner2.jpgGenerally, the “stabilized world” and “comprehensive technology” scenarios overestimated food, services, and material goods for the population. And population was under-estimated by the “stabilized world” scenario. All scenarios matched the remaining non-renewable resources to varying extents. Global persistent pollution was underestimated by both the “stabilized world” and “comprehensive technology” scenarios.

Overall, Turner’s analysis shows that — can you guess it yet? — 30 years of historical data match pretty closely the key features of the business-as-usual “standard run” scenario, which predicted collapse of the global system midway through the 21st century. Conversely, the data did not compare well with other scenarios involving salvation through technology (perhaps too much of it is being diverted to twitter) or stabilizing behavior and policies.


Turner’s analyses also provide some indication of the change in consumption patterns that would likely be required to achieve a sustainable global system. The “stabilized world” scenario assumed a sustainable global average per capita level of material wealth approximately equal to contemporary levels. Currently, of course, the great majority of that wealth is being enjoyed by us in the developed world, which makes up one-quarter or less of the world’s population. If, for the sake of argument, this wealth were distributed evenly across the future global population (assume ~9 billion people), average per capita material wealth would fall to about 1/6th of current levels in developed countries.

Yikes again. Let’s get that cap-and-trade bill passed . . .

[Original source:  Turner GM (2008). A comparison of The Limits to Growth with 30 years of reality. Global Environmental Change-Human and Policy Dimensions, 18, 397-411.]

Emmett Duffy is a Professor of Marine Science of the College of William and Mary's Virginia Institute of Marine Science.  He's also in an ecologist who is an expert in marine biodiversity and its importance to human society. This post was republished with permission from his blog The Natural Patriot, which is dedicated to promoting and cultivating a new and universal idea of patriotism for the new Millennium. 

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