The book deals not only with food shortage, but also with other kinds of crises caused by rapid population growth, expressing the possibility of disaster in broader terms. A "population bomb", as defined in the book, requires only three things:
The predictions came true, but the effects are mainly unfelt in the developed world. The world food production grows exponentially at a rate much higher than the population growth, in both developed and developing countries, partially due to the efforts of Norman Borlaug's "Green Revolution" of the 1960s, and the food per capita level is the highest in history. On the other hand population growth rates significantly slowed down, especially in the developed world Famine has not been eliminated, but its root cause is political instability, not global food shortage On the other hand, in the 1980s and 1990s in a number of countries (first of all in Tropical Africa) population growth rates still exceeded the economic growth ones, and on quite a few occasions political instability was caused just by food shortages (see, for example, Secular Cycles and Millennial Trends in Africa by Andrey Korotayev and Daria Khaltourina [ISBN 5484005604]).
Although Ehrlich's theory influenced 1960s and 1970s public policy, a post-analysis by Keith Greiner (1994) observed that Ehrlich's projections could not possibly have held the scrutiny of time because Ehrlich applied the financial compound interest formula to population growth. Using two sets of assumptions based on the Ehrlich theory, it was shown that the theorized growth in population and subsequent scarcity of resources could not have occurred on Ehrlich’s time schedule. Data actually seems to suggest linear, albeit very strong, growth. For example historical US population growth was more linear than exponential. The world population doubled from 3 billion in 1959 to 6 billion in 1999 and is expected to grow by another 3 billion by 2042 Nevertheless The Population Bomb sold many copies and raised the general awareness of population and environmental issues. Early 21st century analyses of the age distribution of the US population show that growth in population declined after "the pill" was approved for widespread use, though the population continues to grow at a rate of 0.91% per annum That approval was likely influenced by Ehrlich's work. (Reference: Greiner, K. (1994, Winter). The baby boom generation and How they Grew, Chance: A Magazine of the American Statistical Association.)
The Population Bomb was written at the suggestion of David Brower, at the time the executive director of the environmentalist Sierra Club, following an article Ehrlich wrote for the New Scientist magazine in December, 1967. In that article, Ehrlich predicted that the world would experience famines sometime between 1970 and 1985 due to population growth outstripping resources. Amongst other remarks, Ehrlich also stated that "India couldn't possibly feed two hundred million more people by 1980," and "I have yet to meet anyone familiar with the situation who thinks that India will be self-sufficient in food by 1971." These predictions did not come to pass. In the book's 1971 edition, the latter prediction had been removed. An oft-cited cause of these famine aversions is the "Green Revolution", as it was called by the U.S. Agency for International Development in 1968 Another oft-cited cause was the sharp drop in the fertility rate which occurred in the developed world during the 1960s and 1970s.
Hence, Ehrlich argues, affluent technological nations have a greater per capita impact than poorer nations.
Critics have compared Ehrlich to Thomas Malthus for his multiple predictions of famine and economic catastrophe. The leading critic of Ehrlich was Julian Lincoln Simon, a libertarian theorist and the author of the book The Ultimate Resource, a book which argues a larger population is a benefit, not a cost. To test their two contrasting views on resources, in 1980, Ehrlich and Simon entered into a wager over how the price of metals would move during the 1980s. Ehrlich predicted that the price would increase as metals became more scarce in the Earth's crust, while Simon insisted the price of metals had fallen throughout human history and would continue to do so. Ehrlich lost the bet. Indeed such was the decline in the price of the five metals Ehrlich selected, Simon would have won even without taking inflation into account.
In Ehrlich's books, many predictions are made, for example, The Population Bomb begins "[t]he battle to feed all of humanity is over. In the 1970s the world will undergo famines -- hundreds of millions of people are going to starve to death," while in "The End of Affluence", Ehrlich stated, "One general prediction can be made with confidence: the cost of feeding yourself and your family will continue to increase. There may be minor fluctuations in food prices, but the overall trend will be up". According to Ehrlich, the United States would see its life expectancy drop to 42 years by 1980 because of pesticide usage, and the nation's population would drop to 22.6 million by 1999 . Criticizing Ehrlich on similar grounds as Simon was Ronald Bailey, a leader in the wise use movement, who wrote a book in 1993 entitled Eco-Scam where he blasted the views of Ehrlich, Lester Brown, Carl Sagan and other environmental theorists. While of the repeated theorizing Simon complained "As soon as one predicted disaster doesn't occur, the doomsayers skip to another... why don't the [they] see that, in the aggregate, things are getting better? Why do they always think we're at a turning point -- or at the end of the road?"
In his book Betrayal of Science and Reason, Ehrlich discussed these earlier predictions of his and re-affirmed his stances on population and resource issues.
Ehrlich also has critics on the political left. These include Betsy Hartmann, author of the 1987 book Reproductive Rights and Wrongs: The Global Politics of Population Control & Contraceptive Choice. Hartmann accuses Ehrlich and other environmentalists who focus on population control of misanthropy, and believes that such focus is antithetical to activism on issues of social class and feminism.
There has been much criticism of the book from demographers today (chiefly Phillip Longman in his 2004 The Empty Cradle) who argues that the "baby boom" of the 1950s was an aberration unlikely to be repeated and that population decline in an urbanized society is by nature hard to prevent because of the economic liability children become.
Various Indices of Economic Freedom claim that lack of property rights, not high population density, is the real cause of famine. Thus, countries such as China, India, South Korea, and Botswana were able to eliminate their famines by adopting property rights. Likewise, countries such as Ethiopia, Zimbabwe, and North Korea created famines when they abolished property rights. Ehrlich's book does not explain why South Korea is so much better off than North Korea, but an analysis of property rights explains this difference very well.
In a 2004 Grist Magazine interview, Ehrlich acknowledged some specific predictions he had made, in the years around the time his Population Bomb was published, that had not come to pass. However, as to a number of his fundamental ideas and assertions he maintained that facts and science proved them valid.
Among other things Ehrlich had to say was the following:
When I wrote The Population Bomb in 1968, there were 3.5 billion people. Since then we've added another 2.8 billion — many more than the total population (2 billion) when I was born in 1932. If that's not a population explosion, what is? My basic claims (and those of the many scientific colleagues who reviewed my work) were that population growth was a major problem. Fifty-eight academies of science said that same thing in 1994, as did the world scientists' warning to humanity in the same year.
Ehrlich has stated that despite his other work, the predictions of his first book are regularly cited as proof of extensive flaws in the environmental movement. At the same time, Ehrlich also notes that many things critics claim were "predictions" were actually scenarios. In The Population Explosion (1990), in a footnote (p. 295), he writes:
In The Population Bomb we tried to deal with uncertainties about the course of events by using scenarios—little stories about the future as an aid to thinking about it. That was a mistake, because people took the scenarios as predictions, and some concluded that because they had not "come true" the basic message of the book was wrong. But, of course, the entire purpose of the book and the scenarios was to stimulate the kind of action that would prevent events such as those described in the scenarios from occurring. (Unfortunately, as we have seen, much of the action that was stimulated by the food problems of the late 1960s turned out to be a short-term cure which has made the long-term situation worse.) At any rate, we're avoiding scenarios in this book. We would not be surprised, however, if some reviewer dismissed The Population Explosion because the scenarios in The Population Bomb did not actually materialize. Live and learn.