Limits to Growth with the Human Population
On a basic level, each additional individual requires a certain number of resources (food, water, energy, heat, shelter, medical care, etc.). As civilizations develop economically, the per capita consumption of every resource, including energy, also rises.
Thus, if human population grows at an exponential rate, it is reasonable to assume that the rate of consumption of these resources will follow the same exponential pattern.
This condition was first contemplated by Thomas Robert Malthus (1766-1834) who wrote, “The passion for the opposite sex being what it is and unlikely to change…. The power of population is infinitely greater than the power of the earth to produce subsistence for man.”
What Malthus implied was that our population was growing exponentially, while our ability to grow food increased arithmetically. Therefore, humans were bound to reach a point where food and starvation would become a limiting factor. If you recall fromFigure 3-8,Historic Global Energy Consumption, from last week’s blog, you’d notice how the population grew arithmetically until the 1700’s.
What factors allowed human population to change from an arithmetic to an exponential growth pattern?
Malthus predicted that because food production grew arithmetically while human population and the need for food grew exponentially, we would inevitably be unable to feed the world’s population.
In the following chart is a generalized description of Malthus’ predictions. The blue line represents the growth of the food supply over time, and the red line represents the exponentially growing need for food. You can see that for the first period of time our food supply was greater than the population’s demand for food (represented by the portion of the graph where the blue line is above the red line), but then the lines cross as the population soars. This section of the graph, to the right of where the lines cross, where the red line is above the blue line, represents more demand for food than there is supply, and to Malthus an indication of impending starvation.
Figure 2-14 Food supply vs. population.
But it didn’t go quite the way Malthus envisioned. Humans discovered how to use fossil fuels to do work for us. It turns out that the blue line representing food didn’t remain a straight arithmetic line.
An acre of land can be made far more productive with the input of energy Energy can make fertilizer, run the tractors and power the mechanisms and tools. Between 1950 and 1984, the world’s grain production increased by more than 250%, and the amount of energy used by agriculture increased by 5000 %
The world population doubled from around 2.6 billion people in 1950 to about 5.3 billion people in 1990 (just under 40 years) and has nearly tripled today. (7.5 billion in August 2017).
Increased energy input into agriculture is one of the important factors that has caused an increase in the carrying capacity of the globe and an increase the caloric value of many humans’ daily diet.
The diet in subsistence societies is about 2,500 calories per day which requires an input of about 10,000 calories. In the US today, a daily diet of 3,500 calories takes approximately 35,000 calories. So, the ratio of energy in/energy out went from 4:1 in subsistence societies to 10:1 in the US today.
Energy intensive farming practices have allowed for the exponential growth in population and food production since World War II.
Can we continue such growth indefinitely? Logic and arithmetic would suggest the answer is no.
Let’s look more closely at the phenomenon of exponential growth, i.e., growth in a doubling pattern such as 1-2-4-8-16-32-64 … Pick any number in the sequence, for example, 32. Now add up all the numbers that preceded 32 in the sequence 1+2+4+8+16= 31 which is 1 less than the next number in the sequence 32. Pick another number in a doubling sequence and try this yourself. You will find that when you add up the preceding numbers, they always add up to one less than the new doubled number. What does that mean to you and me and the average person on the street?
If we start with the premise that it takes a minimum amount of food to keep one human alive, and the human population doubles, that means that we have to grow somewhere around twice as much food to feed that doubled population than has been grown in human history!
If the number of people on the planet doubled between 1950 and 1990, arithmetic and logic say that in this 40-year period more food was grown than had been grown in the history of the world! According to National Geographic, the world’s population will reach 9.7 billion by the year 2050, essentially doubling again.
Malthus could not have anticipated the Green Revolution which allowed double, sometimes triple, the amount of food to be grown per acre of land. There are limits, though, to how much an acre can produce, and thus our ability to feed ourselves.
In an article called “The Limits to the Green Revolution?” author Lester Brown, founder of the Worldwatch Institute and the Earth Policy Institute, explains
“we are now pressing against the photosynthetic limits of plants…. Plants are not that different from people in this sense…..You can get gains up to a point and then it becomes much more difficult – I don’t know of any scientists who are predicting potential advances in grain yields that are comparable with those we saw in the last half century.”
Norman Borlaug won the Nobel Prize in Biology for his work on hybridization. He was called the father of the Green Revolution. In his first press conference after winning the Nobel Prize, he said that the work of his institute, and any similar work, “would only win us all perhaps twenty years breathing space. The potential resources of food were limited.”
Virtually all the components of the modern farm require the input of fossil fuels and, as a result, are more productive than your great-grandfather’s homestead. But productivity comes with a cost. Insecticides and pesticides find their way into water supplies causing pollution and disease. Plants become resistant to pesticides. The remnants of these products, since they have no natural means for decomposing, persist in the environment and cause harm to biological systems. Despite the increases in productivity and production, the problem of human hunger and malnutrition persists.
Was Malthus correct?
“Action Against Hunger,” an organization which feeds malnourished children, estimates one million children worldwide under the age of 5 die of hunger each year. In the United States, according to the USDA Report Food Insecurity Among American Households, “In 2013, one-in-five households with children were food insecure.”
Let’s investigate further the effect of exponential growth of human population on the resources upon which we depend.
As we saw above, exponential growth is growth in a doubling pattern.
The following analysis is adapted with permission of William Ophuls, author of the landmark book, Ecology and the Politics of Scarcity.
Consider a fictitious resource, Widgiton, necessary for making Widgets. As with all matter, there is a limited amount of Widgiton on Earth.
Let’s assume there is a stock of 50,000 tons of Widgiton and that humans currently demand 100 tons of the stuff each year to keep ourselves well supplied with Widgets. At first glance, it looks like we’re all set for the foreseeable future. 50,000 tons in stock/100 tons per year = 500 years supply. We’ll call this number the static reserve.
Let’s Investigate Further!
If we used the same amount of Widgiton each year, our known supply, or static reserve, would last us 500 years. But is that a realistic expectation?
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
1 |
50,000 |
100 |
49,900 |
500 |
If we extend this analysis out, with a growth rate of 3.5 % per year for 20 years, we find the demand for Widgiton has doubled. So, a 3.5% growth rate yields a 20-year doubling period.
Remember the characteristics of Exponential Growth described above? A doubling pattern. Bingo! That is what we’re talking about.
The same principle applies in the world of banking. The greater the interest rate you earn, the faster your savings double. If you’re an investor, this is the way you make money.
How fast the value of your savings account doubles, Rate of increase (%) Doubling Time (yrs.) 1.0 71 3.5 20 5.0 15 10.0 8 |
Following our 50,000-ton, 3.5% growth scenario described above, here is how the first doubling period (20 years) would go:
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
Start |
50,000 |
100 |
49,900 |
500 |
1 |
47000 |
200 |
49,796 |
482 |
3 |
41000 |
107 |
49,689 |
464 |
4 |
49,688 |
110 |
49,578 |
448 |
5 |
49,578 |
114 |
49,463 |
432 |
6 |
49,463 |
118 |
49,344 |
416 |
7 |
49,344 |
122 |
49,222 |
401 |
8 |
49,222 |
127 |
49,094 |
386 |
9 |
49,094 |
131 |
48,963 |
372 |
10 |
48,963 |
136 |
48,826 |
359 |
11 |
48,826 |
141 |
48,685 |
346 |
12 |
48,654 |
146 |
48,539 |
333 |
13 |
48,539 |
151 |
48,388 |
321 |
14 |
48,388 |
156 |
48,232 |
309 |
15 |
48,232 |
161 |
48,070 |
297 |
16 |
48,070 |
167 |
47,902 |
286 |
17 |
47,902 |
173 |
47,729 |
276 |
18 |
47,729 |
179 |
47,550 |
265 |
19 |
47,550 |
185 |
47,364 |
255 |
20 |
47,364 |
192 |
47,172 |
246 |
21 |
47,172 |
198 |
46,973 |
237 |
After 20 years, the yearly demand has doubled, and what was a 500-year supply 20 years ago is now a 237-year supply.
Now, let’s analyze the second doubling period which ends in year 40. We’re now using 395 tons a year.
After only 40 years of using what we once thought to be a 500-year supply available, only a 105-year supply of Widgiton remains in reserve.
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
41 |
41,544 |
395 |
1,149 |
104 |
At the end of three doubling periods (the beginning of the 62nd year), we find ourselves with only 36.25 years of static reserve left and the resource which initially appeared to have a reserve of 500 years ultimately runs out after only 85 years.
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
62 |
29,560 |
815 |
28,745 |
36 |
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
83 |
4,879 |
1,679 |
3,200 |
2 |
Year |
Starting Stock (tons) |
Current Demand/yr. (tons) |
Remaining Stock (tons) |
Static Reserve (in years) |
85 | 0 |
1,462 |
0 |
n/a |
Let’s suppose our original estimate of 50,000 tons was low, and there actually was ten times the original 50,000 tons available to us. Certainly, that would make a big difference, right? Not as big as you might think. A 3.5% growth rate means the annual demand doubles every twenty years. Thus, an expansion of the original supply by 10 times only buys us another sixty-six years, exhausting the supply of Widgiton in 151 years.
But wouldn’t new technology expand the supply even more? What happens if instead of our original estimate of 50,000 tons, we really have 100 times that amount (5,000,000 tons)? In fact, we gain only a total of 218 years more than our original amount would have.
Next week we’ll discuss the static reserve in further detail!