Visualizing Environmental Science

Human Population Patterns 167

human population. Some experts take a more pessimis-

tic view and predict that our ever-expanding numbers

will cause widespread environmental degradation and

make Earth uninhabitable for humans as well as other

species (Figure 7.9). These population researchers

contend that a massive wave of human suffering and

death will occur. This view doesn’t mean we will go ex-

tinct as a species, but it projects severe hardship for

many people. Some experts think the human popula-

tion has already exceeded the carrying capacity of the

environment, a potentially dangerous situation that

threatens our long-term survival as a species.

Global human population trends are summarized in

Figure 7.10 on pages 12 to 13. Note especially regional

differences in population growth and density.

1. How would you describe human population
   growth for the past 200 years?


2. Who was Thomas Malthus, and what were his
   views on human population growth?


3. When determining Earth’s carrying capacity for
   humans, why is it not enough to just consider
   human numbers?

Small differences in fertility, then, produce large differ-

ences in population forecasts.

The main unknown factor in any population growth

scenario is Earth’s carrying capacity. Most published estimates

of how many people Earth can support range from 4 bil-

lion to 16 billion. For example, in 2004, environmental

economists in the Netherlands performed a detailed analy-

sis of 69 recent studies of Earth’s carrying capacity for hu-

mans. Based on current technology, they estimated that

7.7 billion is the upper limit of human population that the

world can support. Even the low U.N. projection for 2050

exceeds this value (see Figure 7.8).

These estimates vary widely depending on what as-

sumptions are made about standard of living, resource

consumption, technological innovations, and waste

generation. If we want all people to have a high level of

material well-being equivalent to the lifestyles in highly

developed countries, then Earth will support far fewer

humans than if everyone lives just above the subsistence

level. Unlike with other organisms, environmental con-

straints aren’t the exclusive determinant of Earth’s carry-

ing capacity for humans. Human choices and values must

be factored into the assessment.

What will happen to the human population when

it approaches Earth’s carrying capacity? Optimists sug-

gest that a decrease in the birth rate will stabilize the

˜ÛˆÀœ˜“i˜Ì>Ê`i}À>`>̈œ˜Êœ˜Ê>ÊV>Ì̏iÊÀ>˜V…ʈ˜Ê  À>∏ÊUʈ}ÕÀiÊÇ°™Ê

Part of the rain forest in the background was cleared for a cattle pasture. After a few years, the pasture became unproductive, and

erosion degraded the land further. Photographed in Amazonas State in the Amazon River Basin.

Global

Locator

BRAZIL

James P. Blair/NG Image Collection

NG Maps