In the Authors' Preface, they provide important background information to their "30-Year Update": Published in 1972, "The Limits to Growth (LTG) reported that global ecological constraints (related to resource use and emissions) would have significant influence on global developments in the twenty-first century. LTG warned that humanity might have to divert much capital and manpower to battle these constraints -- possibly so much that the average quality of life would decline sometime during the twenty-first century." Then in 1992, the authors conducted a 20-year update of their original study and published the results in Beyond the Limits. "In BTL we studied global developments between 1970 and 1990 and used the information to update the LTG and the World3 computer model. BTL repeated the same message: In 1992 we concluded that two decades of history mainly supported the conclusions we had advanced 20 years earlier."
However, BTL (1992) offered one new finding: "...humanity had already overshot the limits of Earth's support capacity. This fact was so important that we chose to reflect it in the title of the book." If you have not already read one or both of the two earlier volumes, these brief excerpts from the Authors' Preface to Limits to Growth: The 30-Year Update will suggest a context within which to understand and appreciate the significance of what Meadows, Randers, and Meadows share in this third volume.
If I understand their key point, it is this: Humanity's consumption of Earth's resources (i.e. humanity's "ecological footprint") proceeds at an increasingly faster rate than Earth's available resources can accommodate (i.e. its "carrying capacity"). There must be prudent physical growth constraints on consumption in combination with replenishment of the Earth's resources. Otherwise, over time, "the world will experience overshoot and collapse in global resource use and emissions."
The authors clearly identify the global challenge (page xv), explain their reasons for writing this update (pages xviii and xix) in response to that challenge, and then conclude their Preface with the prediction that "it will take another decade before the consequences of [global ecological] overshoot are clearly observable and two decades before the fact of overshoot is generally acknowledged." They intend to provide another update in 2012, on the 40th anniversary of their first book.
In the 14 chapters which follow, Meadows, Randers, and Meadows explain why it is not only desirable but indeed imperative to
1. increase the consumption levels of the world's poor
2. reduce humanity's total ecological footprint
3. support technological advances (e.g. to achieve #1)
4. support personal change (e.g. to achieve #2)
5. think in terms of longer planning horizons
The authors offer a range of alternative scenarios (i.e. ten different "pictures" of how the 21st century may evolve) to encourage their reader's learning, reflection and personal choice. For me, Chapter 7 is especially valuable. Based on their structural analysis of the world, they offer seven general guidelines to expedite transitions to sustainability: extent the planning horizon (#5 previously), improve the "signals" (i.e. early-warning system for global ecology), speed up the response time to ecological crises, minimize use of nonrenewable resources, prevent the erosion of renewable resources, use all resources with maximum efficiency, and slow -- and eventually stop -- exponential growth of population and physical capital.
In the final chapter, Meadows, Randers, and Meadows briefly discuss the agricultural and industrial revolutions and then assert that the next revolution should respond to the need for sustainability of humanity on Earth. They share their vision of the sustainable society which such a revolution could achieve and even provide a ("by no means definitive") list of its dominant characteristics, urging their reader to develop it further. I agree with the authors that a sustainable world "can never be fully realized until it is widely imagined." Hence the importance of their ("by no means definitive") list...hence the even greater importance of having as many other people as possible also imagine precisely what kind of a world they would much prefer to live in.
There are obviously limits to how much of Earth's resources can be consumed or corrupted, without replenishment or purification, before they are significantly depleted and eventually exhausted. However, I believe that almost all limits on human imagination are self-imposed. If so, then there should be no limits on our collaborative efforts to reduce "humanity's ecological footprint" to achieve global sustainability of our precious natural resources if we can but summon and then (yes) sustain sufficient resolve to do so.
