What people worry about

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Here are some of the problems that have led people to worry about the sustainability of our present civilization - let alone the continuation of progress. Some are real and some are imaginary.


Limits to growth scenarios

In 1971 the Club of Rome, an organization of rich do-gooders funded a study by Dennis and Donnella Meadows who did a computer simulations of a model of world future. The simulations took into account population, resources, production and pollution. It assumed that rates of change of each of these variables was a linear function of the values of all the others. There was only one numerical value for each of the variables, i.e. the model didn't distinguish production of different commodities or distinguish different kinds of pollution. Because of the linearity, there was no possibility of saturation of any kind of demand. (If the methodology had been applied to American beef production starting with middle 19th century data, the such a simulation might have predicted that by 1930, each American would eat a cow a day.)

The results were published in a 1972 book Limits to Growth by Donnella Meadows, Universe Books, New York [1973]. . The book concluded that the world would end in disaster, i.e. the population would go to zero. A significant part of the press was in the mood for a disaster prediction and made the book a best seller. Before publishing the book the authors removed the numbers from the axes of the graphs, so that the disaster was not predicted for any specific time.

Economists gave the book a very hard time, and a group at the University of Sussex in Britain did a particularly thorough job. The book is Models of doom; a critique of The limits to growth. Edited by H. S. D. Cole [and others] With a reply by the authors of The limits to growth. That's the American title. The British title is Thinking about the future: A critique of 'The Limits to Growth.

A more recent book with the same author as Limits to Growth and similar methodology is Beyond the Limits: confronting global collapse, envisioning a sustainable future..

My opinion is that the book and methodology are nonsense, because it doesn't take into account saturation of demand and because aggregating all production into one commodity does not allow taking into account the effects of different kinds of production. Very likely, the numbers are wrong too. Our approach is to take different aspects of production into account separately, because they can have very different characteristics.

1996 September note: The Club of Rome now has a Web page. The Club's current views are not quite the same as those of Limits to Growth. In particular, the page contains an article favoring nuclear energy. Perhaps I will have further comment when I have read more of it.


Cancer is partly genetic in origin, but a much larger fraction of cancer has environmental causes. The evidence for this is the difference in the rates of different kinds of cancer in different parts of the world. Here are some examples. While most cancer seems to be of environmental origin, the causes of most kinds of cancer have not been identified. The picture is complicated by the fact that certain substances in the diet protect against certain kinds of cancer.

There has been a widespread belief that many artificial chemicals are significant causes of cancer, and this belief has been confirmed for large doses of certain chemicals.

The very small amounts of artificial chemicals present in foods from pesticide residues and from water are not significant causes of cancer according to a study by the National Research Council published in 1996 entitled Carcinogens and Anti-Carcinogens in the Human Diet.

It appears that cancer is not likely to be a significant obstacle to the sustainability of progress in spite of what some alarmists say. The situation is getting better on the whole.

The on-line Encyclopedia Britannica has a good article on cancer.

Loss of topsoil

See my article on erosion.

Loss of biodiversity

In part this is a genuine problem, and in part it is a matter of values and priorities.

One genuine problem is that much of the recent improvement in agricultural plants is based on finding wild varieties or varieties cultivated in different countries with useful characteristics and breeding these characteristics into the main agricultural varieties. As the world comes more and more to use the products of breeding, other varieties may die out. There are seed banks, but it is feared that they are inadequate and inadequately supported. Moreover, there are many potentially useful wild varieties that haven't been examined yet, and some of them may go extinct.

There is also a problem with fungi, bacteria and insects, but it is less acute.

The solution is to spend more money on the seed banks and on living plant museums and also to preserve some wild areas.

The values problem is that some people put preserving all existing species high on their list of priorities far beyond considerations of human welfare.

Anti-human "man is vile" sentiments have alway had a substantial following in human society. At some times, even majorities have given at least lip service to the idea. The idea that man is guilty of the demise of other species meshes with this general philosophy. In the 19th century the movements that led in the United States to the creation of national parks to preserve natural wonders and wildlife seem to have had less of the accusatory tone of the more recent demands for expansion of wilderness areas.

Certainly we should keep as many species in existence as we reasonably can. On the other hand, current and projected extinction rates are not a threat to the sustainability of progress. We could live with a much impoverished collection of species.

Extinction Rates by Lawton and May gives a 1995 summary.


The last really big famine was in 1958 and 1959 and was associated with Mao Tse-Tung's "great leap forward" in China. 20 million to 30 million people died. There have been lesser famines associated with civil wars, especially when one side found it a good idea to starve the population in the areas occupied by the other side.

There would have been a famine in India in 1966 except that the U.S. sent India 1/6 of our wheat crop. Generosity coupled with worldwide transportation stopped that one. In 1943 there was a famine in India, but British shipping was all tied up with the war (WWII).

Decline in male sperm count

2003 note: There was a lot of excitement about this in the middle 90s. It was claimed that male sperm count in the U.S. was declining, especially in New York. Then someone else said it wasn't declining in New York.

Running out of natural resources

Exploitation of poor countries

Nuclear and other ionizing radiation

Development of drug resistant bacteria

Pesticides in foods

Global warming or cooling or other climate disaster

Tropospheric ozone

Loss of farmland from growth of cities

Less firewood available in "developing nations"

Those populations that have depended on scavenging firewood for cooking are indeed in difficulty. They either have to plant fast growing trees or switch to other fuels. In the main they are switching to kerosene and other fuels used in the somewhat more developed parts of their countries and the world. Switching fuels is easier for them than developing a whole new fuel wood technology and commercial organization. Their backwardness is substantially due to an inadequate commercial infrastructure, and it is easier for them to take advantage of existing models than to pioneer. For this reason, I take a dim view of appropriate technology.

Loss of tropical forest

Exhaustion of fisheries

It seems that the sustainable catch of wild fish in the world is about 100 million tons per year. Recently some important fisheries have declined because of overfishing. Intensive efforts have been made to negotiate international agreements to limit catches to sustainable amounts. These are difficult, partly because fishing is part of many cultures. For example, the Spanish have been fishing the Grand Banks off New Foundland for 500 years. Nevertheless, agreements are gradually being reached.

Farmed fishing is growing rapidly, and for some species, the tonnage of farmed fish is approaching that of wild fish. (More details and some links would be welcome.)

An important technological possibility is fertilizing barren areas of the sea with essential nutrients that are required in small quantities. Iron is the primary nutrient being considered. This would also cause the sea to take up more CO2 and thereby ease the global warming problem.

Send comments to mccarthy @stanford.edu. I sometimes make changes suggested in them. - John McCarthy

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