No matter what the spatial scale, Earth’s surface presents a picture of physical diversity in terms of soil, climates, vegetation, and topography. That diversity offers a range of environmental contexts for people. The geographically informed person must understand how humans are able to live in various kinds of physical environments—not only those of the familiar mid—latitudes but also those that seem less conducive to intensive settlement such as the Arctic tundra and the Equatorial rain forest—and the role physical features of those environments play in shaping human activities.

To live in any given physical environment humans must develop patterns of spatial organization, which take advantage of opportunities offered and avoid or minimize the effects of limitations. Physical systems and environmental characteristics do not, by themselves determine the pattern of human activity. If the incentives are great enough settlement is possible, although at great cost and risk. The trans—Alaska oil pipeline and construction techniques used in tundra—area settlements are evidence of the extent of human ingenuity. However, the environment does place limitations on human societies (e.g., a glaciated region with its complex of features—thin, rocky, water—logged soils and unique landforms—offers few opportunities for commercial agriculture).

A central concept is the idea of carrying capacity—the maximum, sustained level of use of an environment that is possible without incurring significant environmental deterioration, which would eventually lead to environmental destruction. Environments vary in their carrying capacity, and people’s failure to understand it—or their inability to live within it—can lead to environmental disaster. Cyclical environmental change, especially in semiarid environments, can pose particular problems for human use of that environment and can lead to desertification, famine, and mass migration, as has occurred in the Sahel of north-central Africa. The relationship between any environment and its inhabitants is mediated by decisions about how much to consume and in what ways to consume. Energy conservation, water conservation, and recycling can have significant effects on patterns of environmental use.

In modern times humans have used technology as a means of reducing the potential effect of physical systems on human activity. In the United States, for example, the widespread introduction of air-conditioning has allowed people to relocate to the South and Southwest, regions previously considered less suited to settlement. And in various regions of Earth, use of the airplane has made it possible to establish settlements and industries in hitherto inaccessible places. However, the use of technology to overcome physical impediments to human activity can also have wide—ranging and sometimes unexpected consequences. For instance, the attempt to control rivers by building dams and dredging waterways to prevent destructive and life-threatening floods can also lead to diminished soil replenishment, increased water salinity, reduced flow of sediment to oceans, and increased riverbank erosion.

In addition to carrying—capacity limitations, the physical environment often imposes significant costs on human society. Natural hazards are defined as processes or events in the physical environment that are not caused by humans but whose consequences can be harmful. They cost the United States billions of dollars each year. Hurricanes, earthquakes, tornadoes, volcanoes, storms, floods, forest fires, and insect infestations are events that are not preventable and whose precise location, timing, and magnitude are not predictable. Their negative consequences can be reduced by understanding the potential vulnerability of different groups of people and by implementing a variety of strategies such as improved building design, land-use regulation, warning systems, and public education.

Whether the issue is the mitigation of a natural hazard or recognition of carrying capacity, students need to understand the characteristics and spatial properties of the physical environment. It is essential that they be able to translate an understanding of the physical processes and patterns that shape Earth’s surface into a picture of that surface as a potential home for people. That home can hold only so many people or be used only in certain ways without incurring costs. Judgment as to the acceptability of those costs requires an understanding of environmental opportunities and constraints.