In addition to the effects humans have on the environment, it is also important to study how changes in the environment in turn affect human populations. We now know that when land cover is changed from its natural state, the cycles of energy and materials are modified. These changes can lead to a number of consequences, particularly where change is rapid over large areas, including decreased rainfall, more erratic rainfall patterns, increased wind and water erosion, introduction of pests, and changes in local temperature. Repercussions from these changes may be chaotic, unpredictable, and occasionally disastrous.
The local effects of land cover change on humans is more evident in the nonindustrialized countries because they frequently do not have the resources needed to mitigate negative effects. For example, if soil becomes unfertile it can be revitalized through the use of fertilizers, but when local economies prevent access to such inputs for about 80 percent of the world's farmers, other ways to deal with the soil infertility must be found.
3.1.1 Production systems -- When natural production systems are disrupted or replaced, nutrient depletion and modification of soil properties affect humans. As these systems become altered beyond a certain point, the intended land use for the area may no longer be suitable. As the land degrades, crops become less productive and the risk of malnutrition or starvation becomes greater. In cases where restoration is infeasible, it eventually becomes necessary to modify other land to fulfill the desired land use.
3.1.2 Quality of life -- In some instances, changing the natural state of the land results in conditions that degrade general living conditions. Some examples of this include
3.1.3 Natural hazards -- As vegetation is removed from a landscape, the hydrologic cycle is disrupted so that less water is absorbed during rainfall. This results in greater surface runoff during and immediately after a rain, which increases greatly the risk of erosion. Because of the increased runoff, less water infiltrates the soil and ground water is reduced. Thus there are greater chances of floods during historically normal rain events, and increased likelihood of drought long after the rains have ended because of the decreased level of ground water. These effects can be more severe because of the already marginal living conditions.
Globally, the modification of atmospheric circulation patterns over a number of years (for example, as a result of massive deforestation) can also result in increased natural hazard to humans by increasing the frequency, intensity, and unpredictability of severe weather events. Over decades a host of natural hazards may result from sea level rise which can, when accompanied with more frequent severe weather events, result in coastal flooding, crippling property damage, and loss of life.
With environmental shifts, humans (like all organisms) can possibly adapt to changing conditions. Changes in weather patterns, in energy flow and material cycles, or in the natural vegetation have always occurred, but it is now changing at a rate probably unmatched in historic times (or matched by some of the most severe climate changes in Earth history, such as the Younger Dryas cooling event 11,000 years ago).
Human settlement typically responds by either migrating to another area or adapting to the change. The manner of adaptation is either behavioral in the sense of breaking with tradition and adjusting our resource use, or becoming inventive and devising a fresh mechanism to mitigate the effect of the change. In the case of the latter, it is typical for impacted communities to rely upon technological innovation in a rescue or postponement from the fundamental changing of lifestyle. This matches well with the inherent conservatism of individual householders, and of the many economic and political entities whose power is vested in the status quo.
3.2.1 Changing behavior -- In addition to environmental limits, and closely related to them, a region's culture dictates the way its people use the land around them. Traditions formed from the coping of many successive generations have the momentum of centuries, and to this day significantly affect the behavior of people around the globe. While these traditions have weathered many change cycles through recent history, and have adapted themselves to environmental change in the past, it is now difficult to keep up with accelerated environmental change, and with the bombardment of technical suggestions and economic promise. This is particularly significant in cultures where traditions play a very important role (for example, most of Africa and Asia).
Diet and farming are behaviors that can be modified, however this is harder for some cultures. When the availability of water and the quality of land changes, it is frequently necessary to grow crops that are better suited to the new environment. For example, the widespread and very fundamental dependence on rice farming often needs adjustment due to the pressures of change. Although it may seem straightforward on the part of the supermarket culture of North America and Europe to change diet as needed, it often takes years and sometimes generations in more traditional societies to overcome the many cultural and physiological challenges.
Family planning is an issue tightly linked to traditions, but one which has been changing throughout the world. In some countries family planning is encouraged or required by the government in an effort to slow population growth. In the industrialized nations, there has been an overall voluntary decline in the rate of population growth, but many other nations are slower to change because of the considerations and demands of cultural or religious beliefs.
3.2.2 Technological innovation -- The usual technology fix involves modifying natural systems to lessen the rates and effects of change. These modifications can take several forms, including: additional material inputs (such as chemical fertilizers, pesticides and herbicides); innovations such as the development of new grain varieties resistant to certain pests and able to grow on marginal soils; and the redesign of natural features such as modifying river courses to reduce the chances of floods. In many nonindustrialized nations, the technological options are much reduced due to material, financial, cultural or political constraints.
Historically, technological solutions to environmental problems have had a short-term positive effect but an ambiguous or negative long-term effect. It is often difficult to predict the overall effect that modifications to natural systems will have. For example, no one involved in the so-called "green revolution" (a period during the mid-twentieth century when new crops and farming practices replaced traditional agriculture and local crop strains) would believe that the introduction of hybrid crops could create a circle of dependency that would completely usurp traditional economies and forms of government.
In nonindustrialized nations there is a trend to introduce appropriate technology to improve general living conditions and agricultural practices. Appropriate technology is a customizable mix of technology and local resources to provide tools and material flows that can be generated and maintained within the local economy. Examples of this include improved cook stoves that use less wood, handmade farm implements which can be used to improve crop yields, and local intercropping of woody and herbaceous off-field species to provide fodder, poles, fuel, nutrients and erosion control.
3.2.3 Future prospects -- While scientists are collecting more evidence linking land cover change to various environmental consequences, the rate of land conversion is increasing. This is largely due to the increased demands of a growing human population.
Remote sensing technology is a tool that can be, and has been, used to provide objective information about rates of land cover change. Global and local remote sensing data can be used to help educate and inform policy, policy that can influence the ultimate causes that impact land cover and important biological and physical processes. By studying changes in productivity and cover over time, by inferring appropriate land use in particular regions, by providing some understanding of the consequences of future land cover change, and by matching alternative approaches less disruptive than current practices, momentum aimed toward lasting solutions can be gained. As a result, the negative effects on land qualities and on human suffering can be diminished.
Efforts are being made by government and nongovernment organizations to introduce less destructive and more sustainable land management practices. The effectiveness of such initiative relies on the careful integration of suggested adaptations with local customs. As improved information systems continue to monitor vegetation and to monitor the efficacy of these land management compromises, there will be a confluence between the lessons of the past and the suggestions for the future. As a species we still have much to learn, and the provision of objective, synoptic measures has recently and will continue in the future to aid this most crucial education.