In 1972, The Limits to Growth delivered perhaps the most important possible message to modern humans:

• physical growth of the human population and our industrial output cannot continue indefinitely,
• the limits are not too far off, probably closer than a century,
• there is a strong possibility that following a period of overstressing Earth’s systems (overshoot), the quality of human existence will decline significantly (collapse), and
• choices could be made now to avoid this future.

Meadows, Randers, and Meadows based their conclusions on a systems model that described in mathematical terms such factors as population growth, industrial output, agricultural production, and pollution, and how they relate to each other. In essence they created a tool kit for studying how world systems, the systems in which we live, behave.

The original book, with its computer simulations of possible futures, created quite a stir, rising onto the bestseller lists. It also inspired a generation of researchers to study how we humans relate to Earth.

Yet it appears that most people who read the book misunderstood it, taking its computer simulations as predictions of a doomsday future. In fact, the point was not to predict the future, but to present new ways of thinking about our interaction with the Earth, and some tools for analyzing it, in the hope that they would be used to chart a sustainable future.

In the intervening 30 years, the world has proceeded in a way not too different from the standard run from the 1972 LTG. The dominant belief in perpetual growth as necessary and beneficial has, if anything, strengthened. The central message of LTG has been dismissed by many economists as simply wrong.

Fortunately, Meadows, Randers, and Meadows have not heeded the claim that their effort was wasted. They continued to be driven by facts, evidence, and analysis. And they have believed that their message was too important to die.

The 30-year update of the original (there was also a 1992 update entitled Beyond the Limits) presents the same essential message as in 1972. Minor tweaks have been made to the computer model, but its essential operation is about the same. Charts and tables have been updated, and the authors have made an extra effort to be clear in two specific areas where they feel they were misunderstood before.

The first is in explaining what system modeling is all about, why it is a useful tool for understanding world systems, and inviting the reader to consider seriously how the modeling might be right or wrong. The second is in explaining the notions of overshoot and collapse, and trying to convince readers that these are very real possibilities for our world system.

We now have many fewer choices than we had 30 years ago. What was possibility then is reality now. We are now in a genuine state of overshoot, living beyond the Earth’s capacity. If we seriously work on it, we might avoid damaging Earth’s support systems so deeply that a collapse results. The difficult part is that the necessary changes require a complete rethinking of the most basic assumptions of the world economy.

The authors’ conclusions will probably frighten the thoughtful reader, but if you find their conclusions plausible, the question immediately becomes, what can you do to help reverse overshoot and create worldwide sustainability?

Chuck Wright is a renewable energy consultant who has served on the board of the Texas Solar Energy Society, http://txses.org.