Not Evil, Just Romm

UPDATE: Romm at CP makes some significant concessions to error with additions, but can’t bring himself to mention WUWT, credit Willis, or allow any commenters to do so either. He has been “disappearing” critical comments as evidenced by our own commenters reposting their disappeared comments here. It is comical to watch. – Anthony

Guest Post by Willis Eschenbach

Anthony asked me to take a look at Joe Romm’s comments on a new paper called “Evidence for super-exponentially accelerating atmospheric carbon dioxide growth”, by A.D. Husler and D. Sornette. The paper is available on Arkiv.  It’s not peer-reviewed as far as I can determine.

I started to review the paper. I got to the opening comments (and the footnote) on Page 1 referring to the “ecological footprint”. This is a very bad sign, the “ecological footprint” has nothing to do with science. It is an advocacy tool.

Figure 1. Population density expressed as height. Image Credit

Then I got to the footnote on Page 2, and I could go no further. It says:

Thus, a constant growth rate corresponds to a population growing exponentially, with a doubling time given by (log2)/r. As the present growth rate is r(2010) ˜ 1.8% per year, this gives a present doubling time of 38.5 years. If nothing changes, the present 6.8 billion people will be more than 13 billion in 2050! This is in contradiction with projections of OECD for instance and other international organizations, which optimistically expect human population to stabilize around 9 billion individuals.

Other than the gratuitous exclamation mark, why did this stop me from even considering the rest of the paper?

I’ve mentioned before that one of my strengths is that I’m a generalist. Back in 2004 I did an extensive analysis of the relationship between population growth rates and nutrition. No reason, it was never published, I was just curious.

My results showed something very interesting. By and large, if the population growth rate in a country, region, or the world is decreasing, average nutrition (daily calories, protein, and fat per capita) increases. On the other hand, if the population growth rate is increasing, the country cannot feed itself, nutrition declines. The absolute growth rate is not important. It is the direction of the change in growth rate that determines whether people can feed themselves.

In any case, as a result of that 2004 research of mine, I knew that his talk of a “constant growth rate” for global population was nonsense, global population growth rates have been dropping for years. I also thought I remembered the growth rate being lower than 1.8%. I went back to the wonderful FAOSTAT database and updated my figures (note that their figures post-2008 are estimates). Figure 2 shows the actual global population growth rates since 1961:

Figure 2. Annual increase in population as a percentage, 1961 to 2008.

Now that we have the real data on the population, let’s examine his claims.

1.  He assumes a constant population growth rate. In fact, the growth rate has been dropping for half a century.

2.  He says the 2010 growth rate is 1.8%. In fact, it hasn’t been that high in about a quarter century.

3.  He says that the population will be “13 billion in 2050?. This assumes a) the current growth rate is 1.8% and b) the growth rate is constant. Neither one of those assumptions is anywhere near true, so the conclusion is also invalid.

I calculate that if the trend continues, the growth rate will reach zero sometime shortly after mid-century. At that point I calculate the population will be about 9.5 billion. This is in good agreement with the UN FAO midrange estimate of the expected maximum population.

So that’s why I quit reading their paper right then and there. If they can get something bozo simple like the population growth rates that wrong, I fear I don’t really have time to hack my way through their more outré propositions regarding “super-exponential acceleration”, whatever that may be.

Joe Romm swallowed this one whole, opining (emphasis mine):

The paper itself is mostly for math and statistics junkies.  It is essentially agnostic on climate science.  But the conclusions are as stark as any in the climate literature:

• The human population is still growing at an exponential rate and there is no sign in the data that the growth rate is decreasing. Many argue that economic developments and education of women will lead to a decreased growth rate and an eventual stabilization of human population. This is not yet observed in the population dynamics, when integrated worldwide. Let us hope that the stabilization of the human population will occur endogenously by self-regulation, rather than by more stringent finite carrying capacity constraints that can be expected to lead to severe strains on a significant fraction of the population.

No sign in the data that the global population growth rate is decreasing?

You go, Joe.

w.

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