How Many People Can the Earth Support?

The question “How many people can the Earth support?” is useful, though it is seriously incomplete. It focuses attention on the present and future numbers, qualities, activities, and values of humans in their relations with one another and with the Earth. To explain why people are interested in this question, I offer an overview of global human population, economy, environment, and culture. I then review some answers to the question and describe what is involved in answering it. Finally, I suggest actions that could alleviate some of the problems of population, economics, environment, and culture.

The Earth’s capacity to support people is determined both by natural constraints, which some will emphasize, and by human choice, which others will emphasize. In the coming half-century, we and our children are less likely to face absolute limits than difficult trade-offstrade-offs among population size and economic well-being and environmental quality and dearly held values. Foresight and action now might make some of the coming trade-offs easier.

I hope to offer a perspective that differs from the views of those who say that rapid population growth is no problem at all and those who say that population growth is the only problem. A rounded view of the facts should immunize us against both cornucopians and doomsayers. I give more details in my recent book How Many People Can the Earth Support?*

Past Human Population

Population Size and Growth. Two thousand years ago, the Earth had roughly one quarter of a billion people (the population of the United States around 1990). By 1650 the Earth’s population had doubled to half a billion. When the Old World and the New World began to exchange foods and other resources in a serious way, the time required to double the population dropped from more than sixteen centuries to less than two centuries. The human population passed one billion around 1830. The second billion people were added in only one century, by 1930. The next doubling, to four billion, took only forty-four years. Until around 1965, the human population grew like an interest-bearing account in which the rate of interest increased with the balance in the account. Around 1965-1970, the global population growth rate reached its all-time peak, then began to fall gradually and erratically. It still remains far above global growth rates experienced prior to 1945.

In the lifetime of anyone who is over forty, world population has doubled. Never before the second half of the twentieth century had any person lived through a doubling of world population. In absolute numbers, putting the first billion people on Earth took from the beginning of time to about 1830. Adding the latest billion took twelve years.

In spite of this rapid population growth, by demographic and nutritional standards average human well-being has improved. For the world as a whole, life expectancy at birth rose from 46.4 years in 1950-1955 to 64.4 years in 1990-1995, an increase of 18 years. The advantage in life expectancy of the more developed regions over…

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