Saturday, August 30, 2008

Future Alternatives

I merged my two leading models of the relationship between resource consumption and population into one combined population model, which shows better than ever the constraints on future growth. The new model uses a generic definition of “resources,” measured in units of mass, and incorporates access to the resources and response to perceived depletion of resources into the mathematical description of consumption. Renewable resources (“capacity”) are counted as non-renewable resources which don’t begin to be depleted unless consumption exceeds the amount that is replaced.

We have several options:

(1) We can continue business-as-usual, which will result in a catastrophic depletion of resources associated with a population crash. The timing is the same as before, beginning with a population peak about 30 years from now.

(2) If we want to continue the growth in consumption and population we’re currently enjoying, we must access new resources by about 10% per year if we start in 2010. This growth can be sustained for a maximum of another 200 years, when we will be unable to move resources fast enough and be faced with the same prospect we have now – population collapse.

(3) We could stop growth in overall consumption. Beginning in 2010, this would buy us another 30 years or so.

(4) If we could somehow decrease our consumption without adversely impacting population (for instance, by distributing resources to poor people so the reduction doesn’t kill them), then we could stretch our resources longer. If the minimum per capita consumption is what the average was in 0 A.D., then we could stretch our resources no more than about another 1,400 years if we start in 2010 (less if we start later).

(5) We can attempt to increase the amount of renewable resources to a level just above the consumption that could sustain a preferred population size and keep our consumption constant. We would use non-renewable resources only as necessary to adjust to changes in renewable resources (and help make those changes). Starting in 2010, I estimate that to avoid the impending population crash, we would need to increase renewable resources by at least 16% per year while keeping consumption constant. While theoretically we could do this indefinitely, we would only have two years' worth of non-renewable resources to handle contingencies.

(6) We could use a mixed strategy of growth and sustainability. This would involve simultaneously increasing our access to both renewable and non-renewable resources while restricting growth in consumption. I estimate that in the best case (keeping consumption constant) we could extend resources more than 1.6 million years.


Pete Murphy said...

Brad, the kind of decrease in per capita consumption that you've proposed in option 4 would produce a catastrophic economic collapse, which would probably lead to the equally catastrophic population collapse you envision in the other options.

There's really only one viable alternative: reducing our population. You may find my book interesting because it explores a facet of population growth that no one has considered: the effect upon per capita consumption caused by population density rising beyond some optimum.

If you‘re interested in learning more about the important new economic theory proposed in my book, then I invite you to visit either of my web sites at or, where you can read the preface, join in the blog discussion and, of course, buy the book if you like. (It's also available at

Please forgive me for the somewhat spammish nature of the previous paragraph, but I don't know how else to inject this new theory into the debate about population and per capita consumption without drawing attention to the book that explains the theory.

Pete Murphy
Author, "Five Short Blasts"

Bradley Jarvis said...

As Pete suggests, my model predicts a decline in population if consumption is reduced (option 4), which is why I added the caveat at the beginning. I agree that such a break with the fundamental connection between population and consumption is a long shot, but I felt compelled to include it for completeness. I personally favor the last option, which I intend to elaborate on in future posts.

Pete’s allusion to critical population density is a topic I’ve addressed before (see, for example, “Stressful Contact”). Years ago, I learned about the General Adaptation Syndrome (the biological response to increased stress from interference of same-species members in survival-related activity such as eating and sleeping), that is the primary mechanism for death during population crashes in other species. As available resources decrease, competition increases stress that leads to adrenal failure. This effect has long been known by biologists as the source of the correlation between population crashes and critically high population density.

The global economy’s frenzied growth, facing limited resources, is leading to more and more uninvited intrusion of people into each others' lives, which may already be manifesting in violence (recent wars may be international instances of this). This trend is likely to intensify as resources become even more scarce, which is why I advocate increasing resources, especially renewable resources, while limiting consumption to a maximum.

Pete’s suggestion that we should reduce population may be one I’ve seen before (I haven’t read his book), notably in the conclusion of Alan Weisman’s book "The World without Us." The theory goes that if we keep the birth rate below replacement, then the population will humanely decline to a sustainable level; beyond that, we would presumably keep the population constant by re-establishing the replacement birth rate. Some demographers believe that this may happen on its own, as women grow older before having children and the Baby Boomers die off. My model is agnostic on such a suggestion, based as it is on the observed historical correlation between population and the resources consumed to support it.

My personal bias, part of what I’ve been calling an “ideal world,” has focused my discussions on what it would take to avoid a reduction of population for as long as possible. If it proves truly impossible to increase resources enough to support a population at least as large as it is now, then we may need to consider humanely reducing the population to a more sustainable level (what such a level might be is open to question; my model indicates that we are currently using a negligible amount of renewable resources, which implies that it may be very, very low, so that the decline may become the equivalent of a crash).