Overpopulation, as a defined term, generally occurs when a region has exceeded its “carrying capacity.” The “carrying capacity” of a region refers to number of people a region can reasonably support and sustain. When a region has a greater demand for water and food than it can support it is said to be overpopulated.

The “carrying capacity” of an area refers to the maximum number of people a particular area can sustain (keep alive). If this particular isolated area has enough food to support four thousand people, enough water to support three thousand, and enough shelter to support seven thousand we must consider only the lowest number. If there is only enough water to support three thousand people than this is the “carrying capacity” of the area.

The geographic term “ecumene” refers to the proportion of the Earth’s land that is permanently inhabited by human beings. Over time ecumene has increased slightly. This has been caused by a number of factors, but the two most significant are - overpopulation which causes some people to seek new areas for inhabitation and technological innovation that opens up new parts of the world to human inhabitance.

The idea of “cultural landscapes” is most closely associated with the twentieth century environmental geographer Carl Sauer. Sauer argued that all geographic regions, even those which might appear to be unaffected by mankind’s influence, have been impacted by the growth of the human population. His work was important for spreading the significance of environmental studies in the field of geography.

The Fertile Crescent is a region of land between the Tigris and Euphrates rivers in the Middle East (much of modern day Iraq, Syria, and Jordan). It is often referred to as the “cradle of civilization” because it was in these fertile floodplains that the first agricultural communities and later civilizations began to appear. In the thousands of years since then, however, the region (according to Marsh) has been ruined by overuse by mankind. What was once a fecund floodplain is now mostly an arid desert. Marsh uses the example of the Fertile Crescent to support his theory that mankind negatively impacts the environment, especially as population grows.

The “carrying capacity” of an area refers to the maximum number of people who can be realistically sustained by the geography of that area. This number can be affected by access to food, water, shelter, and other significant factors. The “carrying capacity” can often be quite difficult to compute and is extremely fluid and changeable. This is because most “areas” do not solely sustain themselves (think of how it is common for people in the United States to buy mangoes grown in South Asia), but rather exchange sustaining goods with other “areas.”

George Perkins Marsh is one of the most well-regarded geographers and environmentalists of the nineteenth century. In his seminal work Man and Nature (1864), Perkins argued that mankind has a destructive influence on the condition of the environment. His ideas were initially on the fringe of accepted geographic theory, but over the years Marsh has come to be revered as a visionary.