The Ecology of Population Growth by Lester R. Brown

The Rio Blanco river in Texas during the drought of 2011. Photo by Earl McGehee/Flickr/cc

The Rio Blanco river in Texas during the drought of 2011. Photo by Earl McGehee/Flickr/cc

Throughout most of human existence, population growth has been so slow as to be imperceptible within a single generation. Reaching a global population of 1 billion in 1804 required the entire time since modern humans appeared on the scene. To add the second billion, it took until 1927, just over a century. Thirty-three years later, in 1960, world population reached 3 billion. Then the pace sped up, as we added another billion every 13 years or so. We hit 7 billion in late 2011, and have kept right on growing. One of the consequences of this explosive growth in human numbers is that human demands have outrun the carrying capacity of the economy’s natural support systems—its forests, fisheries, grasslands, aquifers, and soils. Once demand exceeds the sustainable yield of these natural systems, additional demand can only be satisfied by consuming the resource base itself. We call this overcutting, overfishing, overgrazing, overpumping, and overplowing.

The most recent U.N. demographic projections show world population growing to 9.3 billion by 2050, an addition of 2.3 billion people. Most people think these demographic projections, like most of those made over the last half-century, will in fact materialize. But this is unlikely, given the difficulties in expanding the food supply, such as those posed by spreading water shortages and global warming. We are fast outgrowing the Earth’s capacity to sustain our increasing numbers.

As human numbers multiply, we need more and more irrigation water. As a result, half of the world’s people now live in countries that are depleting their aquifers by overpumping. Overpumping is by definition a short-term phenomenon.

As human populations grow, so typically do livestock populations, particularly in those parts of the world where herding cattle, sheep, and goats is a way of life. This is most evident in Africa, where the explosion in human numbers from 294 million in 1961 to just over 1 billion in 2010 was accompanied by growth in the livestock population from 352 million to 894 million.

With livestock numbers growing beyond the sustainable yield of grasslands, these ecosystems are deteriorating. The loss of vegetation leaves the land vulnerable to soil erosion. At some point, the grassland turns to desert, depriving local people of their livelihood and food supply, as is now happening in parts of Africa, the Middle East, central Asia, and northern China.

Growing populations also increase the demand for firewood, lumber, and paper. The result is that demand for wood is exceeding the regenerative capacity of forests. The world’s forests, which have been shrinking for several decades, are currently losing a net 5.6 million hectares per year. In the absence of a more responsible population policy, forested area will continue to shrink. Some countries—Mauritania is one example—have lost nearly all their forest and are now essentially treeless. Without trees to protect the soil and to reduce runoff, the entire ecosystem suffers, making it more difficult to produce enough food.

Continuous population growth eventually leads to overplowing—the breaking of ground that is highly erodible and should not be plowed at all. We are seeing this in Africa, the Middle East, and much of Asia. Plowing marginal land leads to soil erosion and eventually to cropland abandonment. Land that would otherwise sustain grass and trees is lost as it is converted into cropland and then turns into wasteland.

In summary, we have ignored the Earth’s environmental stop signs. Faced with falling water tables, not a single country has mobilized to reduce water use so that it would not exceed the sustainable yield of an aquifer. Unless we can stop willfully ignoring the threats and wake up to the risks we are taking, we will join the earlier civilizations that failed to reverse the environmental trends that undermined their food economies.

If world population growth does not slow dramatically, the number of people trapped in hydrological poverty and hunger will almost certainly grow, threatening food security, economic progress, and political stability. The only humane option is to move quickly to replacement-level fertility of two children per couple and to stabilize world population as soon as possible.

Lester R. Brown is one of the world’s most influential thinkers. He started his career as a farmer, growing tomatoes in New Jersey with his brother. After earning a degree in Agricultural Science from Rutgers University, he spent six months in rural India, an experience that changed his life and career. Brown founded the World Watch Institute and then the Earth Policy Institute, where he now serves as President. The purpose of the Earth Policy Institute is to provide a vision of an environmentally sustainable economy, a roadmap of how to get from here to there—as well as an ongoing assessment of progress. Brown has authored many books. This article is from his latest book Full Planet, Empty Plates: The New Geopolitics of Food Scarcity. Supporting data, video, and slideshows are available for free download at

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