Debunking the "limits to growth" model of dieoff.
There are five main variables considered in the model (from the early 1970s!). They are:
Population, food production, industrialization, pollution and consumption of non-renewable resources.
Here are the limits:
Nonrenewable resources are assumed to have no possible renewable substitutes and will last 250 years. (A number pulled out of a hat). Further, it is assumed, however, that other non-renewable resources may replace the initial renewable resource. Technology is allowed to raise efficiency of usage by a factor of 4. (So far so good, quibbling about no substitutes for non-renewables by renewables aside, at least the model accepts that efficiency can stretch resources).
The absolute size of the global economy (agricultural and industrial) is assumed to rise linearly. Further it's assumed that raising global pollution 10 times will have a marginal effect on lifetime but raising it 100 times will have a large effect on mortality. (Arbitrary but let's run with it). In addition, it accepts that pollution may be reduced by pollution control technology by a factor of 4. (Again arbitrary but let's run with it).
Agricultural assumptions state more or less that the world cannot feed 20 billion people.
Population is assumed to be uncontrollable even with contraceptives, based on the "fact" that the average preferred family size, even for a wealthy and healthy population is 3 children or more always.
(May be based on statistics. I can see flaws but let's run with it.)
With all of these assumptions, we get the population growing to nearly 10 billion by 2060-2070 and then collapsing due to pollution, failure of agriculture and non-renewable resource depletion.
If we take the efficiency combined with pollution control model and assume unlimited resources, the population still crashes, although it gets to nearly 20 billion before doing so, and the economy grows much larger before crashing along with the population.
There are significant flaws with these assumptions.
Population is static or declining in all rich countries with the exception of the United States, which is (barely) above replacement levels. Clearly raising income limits population growth.
Agriculture: There is more than enough to go around even today, but yet, people are starving. Obviously the availability of enough food is not the limiting factor. A realistic assessment shows that incomes are too low. Interestingly it seems that the very poorest countries are the ones with the highest birth rates. Putting these two together, deductive logic shows that raising incomes should therefore limit population. And it does, as is shown by 40 years of data after the model was proposed. In addition, there is significant effort in the non-agricultural area to produce non-conventional food from sources such as algae (which, while not currently affordable for anyone outside the rich world, are in theory, capable of feeding billions of people on non-agricultural land)
Substitutes for non-renewable resources
If we look at the end-use for *necessary* non-renewable resources, they fall under the categories: Heating, Cooking, Fertilizers and Transport.
As JD has shown on his blog (and here too) there are *several* substitutes in all of the areas that do not need non-renewables. In the case of Heating, Cooking and Transport electricity is an adequate substitute. In the case of fertilizer systems changes might be needed at the societal scale for phosphate fertilizer, and nitrogen fertilizer is readily available from electricity and air.
The assumptions are wildly inaccurate. Pollution can be reduced down to close to zero at considerable expense and reduced to tolerable levels much more inexpensively.
I thus reject the limits to growth model which (like the peak oil dieoff model) is so flawed as to be unusable.