Dr. John Henrik Clarke

Principal Findings

Rapid growth in the world's population cannot continue through the 21st century and will come to an end either by human decision and action or by an uncontrollable increase in deaths.

Over the past 70 years - roughly one lifetime in many countries - the human population grew from 1.8 billion to 5.4 billion. For every person alive 70 years ago, there are now three. Such rapid growth cannot continue for even another generation. Fertility must decline, or mortality will increase.

But for now the growth continues. Currently the world's population is growing faster than ever before. Each year, 90 million people are added to our numbers, the demographic equivalent of another Mexico. Just a lifetime ago, we were adding only 15 million people per year.

If drastic declines in human fertility (or very large increases in mortality) occur over the next five years, it would be possible to stabilize the human population at about twelve billion within a century. Virtually all of the additional growth - more than six billion - would occur in the poorest, least industrialized countries of the world, often called the "South." The population in the South would grow to over ten billion. The population in the industrialized countries of the "North" would remain at about its current size, a little over one billion.

For such a rapid drop in human fertility to occur, it will be necessary to change the religious, social, economic and legal factors that shape couples' decisions on the number of children they have. Safe and effective contraceptive services must be available, but most important, religious teachings and social, economic and legal circumstances must shift to encourage small families. Child labor, for example, must cease to provide an economic benefit to parents.

It will be difficult to provide 11 to 12 billion people with even such basic necessities as food. Of the 14 billion hectares of land on Earth, only 3.3 billion hectares are potentially arable. At current yields, 0.26 hectares per person are needed to feed the human population; thus at current yields, 3.1 billion hectares would be needed to feed 11 to 12 billion. Only 1.5 billion hectares are currently in production. Since in most cases the best lands are already in use for agriculture, and the remaining lands are already used for grazing or some other use, a doubling of the land in agricultural production would be expensive and disruptive.

Doubling the world's agricultural lands would also cause enormous environmental damage. The potentially arable land that is not now in use - especially land in the tropics - is habitat for a large number of species. Doubling the amount of land in agricultural production would lead to massive extinctions. Even with modest growth in the amount of land in production, a third of all the species that were alive a lifetime ago will become extinct - gone forever - within another decade or two. By 2015, hundreds of species are projected to disappear daily.

If we are to meet the food needs of up to 12 billion people by the end of the 21st century, it is essential that agricultural yields continue to be increased - and in ways that are sustainable. Although conventional technologies can probably double yields, there are increasing questions about the sustainability of conventional agricultural technologies. Furthermore, the promised benefits of yield increases through genetic engineering may be delayed and more modest than expected.

The so-called Green Revolution began about 1950. For the first time, yield-increasing technologies (plant-breeding genetics, fertilizers, pesticides and pumped irrigation) were applied extensively and systematically during the last half of this century, increasing yields dramatically and preventing serious food shortages.

But the Green Revolution also changed agriculture radically, making it dependent both on environmentally destructive practices (especially the use of pesticides, fertilizers and irrigation) and on fossil fuels. Energy used for corn production in the United States, for Example, has increased by a factor of four since 1945. The future of human food supplies is now closely linked to the future of energy supplies.

Global energy supplies and prices are likely to become more unstable and erratic in the decades ahead. Even at present rates of consumption, most of the world's petroleum would be burned within the lifetime of a child born today. If consumption were to increase enough to fuel economic growth in the South, the petroleum supplies of the world would disappear even more quickly. The most pressing constraint on the use of petroleum, however, may not be supply of the resources, but disposal space for its principle combustion product - carbon dioxide.

The concentration of carbon dioxide in Earth's atmosphere is increasing around the world, largely because of the combustion of fossil fuels in the industrialized North. Within the lifetime of today's children, global concentrations of carbon dioxide are likely to reach twice pre-industrial concentrations. Such high concentrations are expected to cause planet-wide changes in temperature and weather patterns. Such changes would seriously disrupt agriculture throughout the world as early as the first half of the 21st century, and during the second half would lead to a sea level rise of 20 to 30 centimeters - enough to force the resettlement of hundreds of millions of people and the abandonment of some island nations.