Administrator’s note: Several months ago GIM was lucky enough to be able to arrange for Dr. Russell Hopfenberg to respond to readers’ comments and questions concerning his important work on the links between food supply, carrying capacity, and population growth. My own summary of that work and its background, along with initial reader comments, is here. Additionally, since I wrote that post, Russ has developed an informative slideshow featuring his ideas. Russ’s responses to those initial comments, and readers’ subsequent questions and comments, are here. If you’re not familiar with the ideas involved and the prior discussion here, those links will help you get up to speed.
Now I’m pleased to post Russ’s follow-up responses to that second batch of reader comments linked to above. To my knowledge, GIM is the only website to have had the chance to present a dialog on this work between Russ and interested readers. The content which has emerged has helped readers better understand these underappreciated ideas. My thanks to Russ for his generosity in participating in this illuminating process! — JF
_________________________________________________________
By Russell Hopfenberg: 
I’d like, once again, to extend my thanks to John Feeney and Steve Salmony for their help with this discussion. Also, thanks to those who participated in this process by either asking questions, responding to my answers, or reading and integrating this information.
Trinifar: For decades the world population growth rate has been declining — see for example here. As Russ says, “… the declining birth rate occurs in countries that have traversed the DT.” It would be interesting to know how much of that decline is due to DT traversal and how much (if at all) to food supply limits.
RH: Regarding the growth rate, this is absolutely true. Now, let’s take a moment to analyze this reality. A growth rate of 3% per year with a population of 2 billion makes the population 2.06 billion the following year — an additional 60 million people. A growth rate of 2% per year, a 1/3 reduction in the growth rate, with a population of 6 billion makes the population 6.12 billion – an additional 120 million people. That’s twice as many additional people as with the higher growth rate!! At some point, our population size will hit the tipping point of ecological disaster and the growth rate won’t matter. As for the DT itself, the DT is a dependent variable. This means that it is a function of something else. That something else is, among other things, food availability. Also, according to the Brundtland Report, it would take more than ten planet earths to usher a population of 6 billion people through to stage 4 of the DT.
Trinifar: Yet it occurs in DT stages 3 and 4 (as Russ notes above) and that includes the US, Canada, Europe, and Japan — a good portion of the world. Is Russ only talking about the parts of the world in DT stages 1 & 2?
Growth is Madness! 