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Household age and sex composition and life cycle stages are also important factors in frontier LUCC. Although young children divert household labor resources from agriculture, older children contribute labor to the farm or capture public access resources such as firewood, game, and water. The settlement life cycle of farm homesteads also helps to explain when and where forest clearing will occur 52 , Immediately following settlement, deforestation is high as land is cleared for subsistence crops 51 , A later deforestation pulse may occur as farms move from subsistence to market-oriented crops or expand into livestock.

These processes are enabled by children growing old enough to provide labor or capital investments through, for example, remittances to the farm household Despite the high fertility of remote rural populations, migration remains the primary source of population growth in forest frontiers Indeed, at a key point along the forest transitions causal chain, in-migration is a necessary precedent to frontier deforestation.

Migration will remain a major driver of frontier forest conversion, often in a leap-frog manner, as more established farm households send younger family members as migrants to the new frontier Although population dynamics are central to LUCC, in all cases population exerts its influence synergistically with other factors. Demand for agricultural land among small holders directly impacts forest conversion, whereas, owing to market forces, urban and international demand for forest and agricultural products further contribute to LUCC through logging and large-scale agriculture.

Political and institutional factors also play an important role in shaping LUCC. For example, government investments in roads, subsidies to the agricultural sector, or land tenure policy can directly influence deforestation rates. Such effects are well researched in the Brazilian Amazon 56 — Cultural preferences can also affect LUCC, such as the desire for cattle as a status symbol among Central American frontier farmers Thus, intervening variables help explain inconsistencies in population-LUCC dynamics Changing the scale of analysis reveals examples in which population growth declined yet deforestation accelerated, population growth was accompanied by reforestation, or population growth attended a number of different human-environment responses Examples of this are evident in the literature for Latin America where many nations have experienced declining rural populations but continued deforestation In parts of the Brazilian Amazon, forest conversion has been driven increasingly by exogenous factors, such as the global demand for soybeans, and owing to increasingly mechanized farming, the region has also experienced rural population decline Interestingly, the same association—rural depopulation and continued deforestation in Ecuador and Brazil—results from a completely different causal mechanism in the two cases, highlighting the importance both of scale and place-based effects.

Similar scale-dependent phenomena emerge in Asian forest frontiers. Land-cover dynamics are the most evident mark of human occupation of Earth. Links to population are both obvious without human population presence there is no human impact on forests apart from acid rain and exceedingly complex, e. A challenge for future research is to disentangle the contributions of population and other dynamics across spatial and temporal scales. For example, more research is needed at the mesoscale subnational and to build causal chains across spatial scales. A diversity of research methods needs to be combined to improve our understanding of these space-dependent links, including remote sensing, geographic information systems, ecosystem process and multilevel modeling, surveys and interviews, participant observation, and stakeholder analyses.

Land-cover change research also considers changes in the quality of land resources as a result of human uses, which is the focus of this section. Perhaps the most contentious debate in the population-environment literature concerns the relationship between increasing population density in subsistence agricultural areas and land degradation or improvement.

This is, in part, the result of widely differing estimates regarding the extent of land degradation, with global estimates ranging from 20 to 51 million km 2 This section considers arguments and evidence marshaled by two major schools of thought: In the VCM, it is hypothesized that there are a number of positive feedback loops that contribute to a downward spiral of resource depletion, growing poverty, and population growth.

An elaboration of these linkages can be found elsewhere 29 , 65 , but in its simplest form, the model describes the following causal connections: High fertility contributes to population growth, which further increases demands for food and resources from an essentially static resource base; the declining per capita resource base reinforces poverty through soil fertility loss, declining yields, and poor environmental sanitation; and poverty, in turn, contributes to land degradation by increasing incentives for short-term exploitation versus long-term stewardship and because poor farmers lack access to costly fertilizers and other technologies.

The implication of these reinforcing linkages is that, absent intervention, the circle will continue and soil fertility will decline until the land is no longer suitable for crops or pasture. Economists have been among the major proponents of the VCM. Thus, household-level responses to resource scarcity can lead to problems at the societal level as each household copes with increased risk and uncertainty by maximizing its number of surviving children.

Yet, several other indicators of environmental decline had no significant relationship to either desired fertility or pregnancy outcomes, and the actual relationship to desired fertility depended in part on whether the respondents were men or women. Thus, although anecdotal evidence is abundant and development policy-making has been heavily influenced by VCM assumptions, there is only qualified support for the hypothesis in the few existing quantitative studies. The Boserupian or intensification hypothesis has been tested in a number of studies spanning Africa, Asia, and Latin America.

A frequently cited study by Tiffen et al. From to , the population of Machakos District grew sixfold, from , to 1. The region was also isolated from national markets, and there were colonial restrictions on access to certain lands and crops. In the s and s, a new form of terracing was propagated by local work groups, agricultural systems shifted from livestock to intensive farming with emphasis on higher-value crops, feeder roads were built to market towns, and market towns developed with agricultural processing facilities and other small industries.

By , the value of agricultural production had doubled on a per capita basis. Many factors led to a positive outcome for this region, including infrastructure development, market growth, private investment, increasing management capacity and skills, self-help groups, food relief during drought, and secure land tenure. This study confirms the basic Boserupian hypothesis: Yet even in this textbook study, other researchers working in the district found important social differentiation in livelihood improvements, land alienation, and government-imposed limitations on mobility—elements that tend to mar an otherwise rosy picture Outcomes were assessed in four domains: Taking pains to point out that in none of these regions were indicators under all four domains positive, the author nevertheless found some common ingredients that resulted in improved or stable soil fertility and yields despite rapid population growth and high densities.

These ingredients include markets for agricultural produce, physical infrastructure, producer associations, knowledge management, and incentives for investment and income diversification. He concludes that productivity enhancements respond to economic incentives and that the capacity of resource-poor farmers to invest in on-farm improvements should not be underestimated.

They found support for the induced intensification hypothesis, with yields largely keeping pace with or exceeding population growth despite high population densities persons per km 2. Soil conditions in Bangladesh are, on average, much better than in dryland Africa owing to deposits of alluvium during monsoon season flooding and therefore can support far higher densities.

They posit that, as smallholders come in contact with the market economy, their redundant production is reduced, and their aspirations increase. Although cropping intensities on average increased significantly in one village almost tripling , they also found increasing production disparities, with large land holders accounting for most of the surplus production, whereas the growing number of landless suffered shortfalls and malnutrition.

They conclude that Bangladesh passed several threshold steps at points along its path towards intensification in which Malthusian outcomes of involution and stagnation might have occurred but were fortunately averted. As these case studies make clear, population is but one among many factors that influence degradation or intensification. Other variables that are of crucial significance include institutional factors land tenure regimes, local governance, resource access , market linkages road networks, crop prices , social conditions education, inequality of landholdings , and the biophysical environment itself original soil quality, slopes, climatic conditions.

Thus, it would appear that population growth is neither a necessary nor sufficient condition for either declines or improvements in agricultural productivity to occur. Population growth can either operate as a negative factor, increasing pressure on limited arable land, or a positive factor, helping to induce intensification through adoption of improved technologies and higher labor inputs. Where it does which depends on factors in the economic and institutional realms. This conclusion is supported by two ambitious meta-analyses of studies that looked at dryland degradation or desertification and agricultural intensification 76 , The authors reject both single-factor causation and irreducible complexity but propose instead that a limited number of underlying driving forces, including population, and proximate causes are at work to produce either degradation or intensification.

Although population can perhaps be discounted as the only relevant variable, there is little doubt that rapid population growth in poor rural areas with fragile environments can be a complicating factor in the pursuit of sustainable land use, especially because policies and markets are rarely aligned in such a way as to produce the most favorable results. Furthermore, trends on the basis of past precedents can only be extrapolated with caution, because the exact locations of thresholds in any given system are still largely unknown The water cycle ties together life processes.

It is fundamental to the biochemistry of living organisms; ecosystems are linked and maintained by water; it drives plant growth; it is habitat to aquatic species; and it is a major pathway of sediment, nutrient, and pollutant transportation in global biogeochemical cycles Population-environment researchers have not dedicated the same level of attention to population dynamics and water resources as they have to research on land-cover change, agricultural systems, or climate change.

Yet there are clear relationships between population dynamics and freshwater abstraction for agricultural, domestic, and industrial uses, as well as emission of pollutants into water bodies. Human settlement is heavily predicated upon the availability of water. A map of global population distributions closely tracks annual rainwater runoff, with lower densities in the most arid regions and as well as the most water abundant, such as the Amazon and Congo Basins.

Whereas the former areas are water constrained for agriculture, in the latter areas, year-round rainfall in excess of mm has rendered these environments less favorable for agriculture owing to soil leaching and oxidation and more favorable for human and livestock diseases. As demand for food increases with growing populations and changing tastes including growing demand for animal versus vegetable protein with its far greater demands for water , it is expected that water diversions for agriculture will only increase.

Northern and southern Africa and the Middle East already suffer absolute scarcity. As population grows and water resources remain more or less constant, many countries in the rest of Africa are projected to fall below m 3 per person Perhaps because such water resources are hidden underground, groundwater resource depletion could potentially remove some agricultural areas from the map. Vorosmarty, EM Douglas, personal communication. Groundwater levels in India have been dropping for more than a decade owing to the unregulated tapping of aquifers 83 , rendering some semi-arid regions vulnerable to shortages.

In the lower delta of the Ganges-Brahmaputra Basin, upstream diversions at the Farakka Barrage, rather than local demands for irrigation water, appear to be causing dry season groundwater deficits and intrusion of the saline front, illustrating how complex basin-wide hydrological connections complicate the attribution of population impacts Other studies at the local level reveal a similarly complicated picture.

Research in the Mwanza region of western Tanzania finds that accessible runoff varies significantly across a relatively small area and that population density closely tracks available water Migrants to towns were generally less likely to have access to water from standpipes and more likely to rely on unimproved wells. Rural-urban migration is not correlated to relative water scarcity in places of origin but rather to proximity to roads and to towns. The researchers conclude that high fertility—a traditional adaptation to peak labor demands during the short cropping season—increases the problems of water access and supply maintenance in agricultural and domestic spheres.

But they also note that gloomy prognoses about future water shortages often fail to acknowledge that large portions of developing country populations never have had the kind of access to water, or levels of consumption, deemed necessary by international bodies. In the Pangani Basin of northeastern Tanzania, a complex set of factors is leading to water conflicts Population is one factor: Owing to high fertility and migration, rural population is doubling every 20 years, and the population of towns is doubling every 10 years.

But other factors include water extraction and land alienation for export flower production and protected areas, growth and mobility of livestock herds, declining summer runoff from glaciers on Mount Kilimanjaro owing to global warming, and hydroelectricity generation.

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The greatest conflict is between farmers and pastoralists, as farmers progressively moved into areas previously considered too marginal for agriculture and pastoralists were squeezed by restrictions on grazing areas owing to newly established protected areas. In recent years, the pressure on land has led to stresses on water and other resources, leading to heavy out-migration from the basin.

The Metropolitan Region of Campinas the 19 core municipalities of the AR saw high, though declining, average annual population growth rates during the — period: The authors find that problems in the form of urban growth and the patterns of population distribution during these three decades have accentuated water quality problems because the rapidity and low density of growth meant that water supply and sanitation infrastructure could not keep up. Water supply infrastructure mostly surface reservoirs as groundwater is scarce did not kept pace with population growth, and the situation was reported as critical as of the mids.

In response, state water basin agencies are applying some institutional solutions such as fees for water withdrawals and restrictions on residential development, as well as some technical ones, particularly the treatment of waste waters. In summary, as in other areas, the relationship between population dynamics and water resources is complex. At the aggregate level, other things being equal, population growth most assuredly does reduce per capita water availability. Yet there is more to population change than growth alone, and rarely are other factors equal, so the specific impacts of population dynamics on water often come down to a complex array of place-specific factors that relate to economic and climatic changes, agricultural and industrial technologies, sewage treatment, and institutional mechanisms, to name but a few.

One of the challenges to research in this area is the common property nature of water resources, and another challenge is caused by rapid regulatory changes as water resources become scarcer, which alters the institutional context. The field could use more basin or watershed studies to understand how variables such as population and climate change may affect future water availability and required institutional responses Basin-level population-development-environment modeling would also help understand and resolve competition between urban and rural water uses as the world becomes more urbanized From the earliest times, the preponderance of global economic activity has been concentrated in the coastal zone 92 , with settlements often growing on the continental margins to take advantage of overseas trade and easy access to the resources of the rural hinterlands.

As a result, the coastal zone has attracted large and growing populations, with much of their growth attributable to migration rather than natural increase Coastal and marine environments are very important for human health and well-being, and they are also quite vulnerable to anthropogenic impacts. Population growth is often named as the driver of coastal and marine environmental problems, whereas proximate causes can be traced to specific practices A recent study highlights how the Kuna population an indigenous population in Caribbean Panama has practiced coral mining and land-filling for decades in response to population growth The Kuna gradually enlarged their island landmass to adjust for their growing population by building coral walls out into the water and then filling in the enclosed areas with corals, sea-grass, and sand.

In addition to direct loss of coral reef, consequences include coastal erosion and a local increase in sea level. This example provides a clear and direct link between population growth and coastal degradation. Population growth can lead to many other coastal and marine environmental disturbances. For instance, tropical mangroves are being converted to fish and shrimp aquaculture farms, which undermines coastal protection and decreases natural habitat that many fish species use for reproduction.

Expanding coastal cities undermine natural protection from storms and hurricanes as well as increase pollution and runoff. Additionally, untreated sewage and agricultural runoff continue to be a worldwide problem. Although listed as a driver, like other issues, the impact of population size and growth depends on many other factors such as the sensitivity of coastal systems to stress, local institutions, and global markets. For example, demand for shrimp is the ultimate driver of mangrove loss, and sewage treatment systems and no-till agriculture could significantly reduce nutrient loading in coastal areas.

The relationship between human activities and environmental impacts are hard to assess and regulate in coastal and marine environments because the environmental resources are almost always governed by common property resource CPR management systems, whereas terrestrial environments are generally managed by the government or private sector.

CPR management systems may be especially vulnerable to disruption caused by in-migration or urbanization. However, the social and economic context largely determine whether in-migration and population pressure disrupt the CPR system and thus cause environmental degradation 98 — Thus, a significant recurring theme in this research is that the social and economic context in which the population is changing as well as when, how, and with whom people interact is more important in determining the impact on the environment than simply demographic change , Studies in developing countries on migration and the marine environment have focused on a mediating variables approach, such as how technology, local knowledge, social institutions of kinship or marriage, and markets mediate the role of population in resource extraction and consequent environmental degradation or enhancement.

For example, some work has hypothesized that migrants misuse resource extraction technologies, which leads to environmental degradation In a coastal Brazilian population, technological change imposed by outsiders who lacked knowledge of the ecological and social context of the community contributed to decreased ecological resilience , and rapid in-migration and technological changes in sea cucumber fishing techniques in the Galapagos led to a collapse in the sea cucumber industry Thus, population-environment researchers have begun to incorporate other social theories such as social capital and migrant incorporation to understand when population pressures do not necessarily degrade the environment Most studies have found that, in systems with strong land tenure or social capital, migrants do not disrupt the environment and are able to develop local knowledge that mitigates environmental impacts — A case study in the Solomon Islands contests the notion that sea tenure regimes are weakened by in-migration and population growth.

Rather, potentially negative impacts of population pressure on the environment are diminished significantly with greater reciprocal ties among close kin or neighbors , Similarly, intermarriage between a migrant and a nonmigrant in Sulawesi, Indonesia, has been shown to mitigate the otherwise negative association between migrant households and coral reef degradation Migration has been the most studied component of population dynamics in coastal and marine environments.

Yet, urbanization and tourism are other primary human drivers affecting coastal ecosystem quality , Fourteen of the worlds largest 17 cities are located along a coast; this affects freshwater flows to coastal estuaries, sewage emissions, and ecological processes at the land-sea interface Also, without careful planning in anticipation of a growing tourist market, cultural and ecological resources may be over-exploited, resulting in unsustainable development, as is the case in Turkey Human impacts on coastal and marine environments are not a simple function of population size or density.

As the aforementioned studies suggest, technology, knowledge systems, social cohesion, common property systems, migrant incorporation, and the economic and ecological context in which these interactions take place all play an important role in population and environment research, especially in developing countries. Nonetheless, coastal and marine environments continue to be among the most threatened ecosystems in the world, owing in part to the sheer scale of detrimental human activities associated with urbanization along the coasts, continued population growth, and a growing number of tourists in search of coastal amenities.

An unresolved issue in this area of research—as in the case of LUCC research—is how to spatially and temporally link populations and human activity to a specific environmental outcome. This is especially difficult in marine and coastal ecosystems because environmental boundaries are fluid. Also important is the impact of local and global consumption on marine and coastal environments.


For instance, per capita consumption of seafood is high in many traditionally seafaring countries even though population sizes are low , and specialized tastes for rare species can have dramatic impacts on fish stocks Further research is needed to assess how population-environment linkages in marine and coastal areas are influenced by the global food trade connecting consumers and producers from opposite sides of the world. Even when they are connected to the electric grid, some two billion poor people in the developing world still largely rely on biomass to meet their energy needs.

That leaves approximately 4. As concern mounts over the health impacts of urban air quality particularly in developing countries and the potential adverse effects of climate change across multiple systems and sectors, population-environment researchers have paid particular attention to understanding the demographic drivers of energy consumption. Although it is clear that there are vast differences in consumption levels per capita energy consumption in the United States is 48 times what it is in Bangladesh and 4.

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  • Hence, we review a number of empirical studies that examine population-energy linkages in a systematic and quantitative manner. In studies of energy consumption researchers have found that it is more appropriate to use the household rather than individuals as the unit of analysis because a large portion of energy consumption related to space conditioning heating and air conditioning , transportation, and appliance use is shared by household members.

    This sharing results in significant economies of scale, with large households generally showing lower per capita energy use than small ones 29 , Energy studies have identified a range of household characteristics as key determinants of travel patterns — and of other types of residential energy demand, such as for heating, cooking, and operating domestic appliances — In a pioneering study, MacKellar et al.

    However, this study did not take into account the lower energy requirements of smaller households, so it likely exaggerated the contribution of the growth in household numbers to energy use. The average age of residents is positively associated with per capita energy consumption, whereas household size and urban location are negatively associated.

    To explore the importance of adopting adequate demographic variables in understanding transport-related energy consumption, Prskawetz et al. Therefore, household characteristics can impact aggregate demand for car use via differences in demand across households as well as likely changes in household composition.

    In studying demographic impacts via energy consumption on air pollution, scientists have identified a number of important factors that jointly determine pollutant emissions, including the familiar elements of the IPAT identity—population, affluence, and technology as reflected in energy and emissions intensities In quantifying the impacts of population on air pollution, researchers have reached different conclusions depending on which pollutants are under study, in which locations, at what scale, and for which time periods.

    For instance, a study of California counties shows that population size significantly contributes to the increase of the reactive organic gases NO x and CO and has little impact on PM 10 and SO x , which are derived more from production activities Population size shows no significant relation to ground-level ozone because ozone is very difficult to measure at specific sites owing to its nature as a diffuse secondary pollutant In research using national-level data, researchers found an almost linear positive correlation between population size and CO 2 emissions , , , and an inverted U-shaped curve for SO 2 However, a more recent study of Canadian provinces over the period — suggests that population size has an inverted U-shaped curve with CO 2 emissions as well, which is at odds with previous literature investigating these variables for other regions and time periods The same inconsistencies in the relationship between population size and emissions of various pollutants are in evidence when examining other population-related variables.

    However, caution should be used in interpreting these results because the studies only cover short time periods 10 to 20 years in which there were only small changes in the demographic variables. Because of the complexity of population interactions as well as political issues, population issues were not considered in formulation of the Kyoto Protocol and have also been largely excluded from the Intergovernmental Panel on Climate Change IPCC assessment reports , although population projections are an integral part of the Special Report on Emissions Scenarios SRES The original emissions scenarios were constructed in using population projections with a base year of Although the projections used in the SRES were largely consistent with actual population sizes for the — period, the projections to and beyond were higher than more recent projections see the text, above, on global trends in population and consumption 11 , , Therefore, even though the scenarios continue to serve as a primary basis for assessing future climate change and possible response strategies, the Fourth Assessment Report of the IPCC is based on slightly lower population projections than the Third Assessment Report under the A2 scenario, which describes an economically divided world with slow technological progress and high population growth.

    Consideration of demographic factors beyond population size, such as changes in age structure, urbanization, and living arrangements, which as discussed above are important in modeling future energy use, are not accounted in the SRES population assumptions. Making progress in this area requires a better understanding of the scope for future demographic change as well as methods for including demographic heterogeneity within energy-economic growth models used for emissions scenario development.

    Simultaneous and consistent projections of population, urbanization, and households are a challenging demographic tasks Recently, Dalton et al. Their research shows that including age heterogeneity among U. Those effects are believed to be much larger for the developing world, where more significant demographic changes such as population growth, aging, household nuclearization, and urbanization are occurring. One of the reasons natural scientists have found population to be so appealing as a human dimension of environmental change is that data are readily available in contrast to other human variables such as values, culture, and institutions , projections are reasonably reliable , and population can be treated in models in a manner that is analogous to all the other quantitative variables.

    This has promoted something of a reductionist view of population-environment interactions. Fortunately, a growing number of natural scientists are beginning to appreciate that humans interact with the environment in more ways than their raw numbers often imply. Populations are composed of people who collectively form societies, and people and societies cannot easily be reduced to food and material demands that result in some aggregate impact on the environment. The new understanding builds on the concept of coupled human-environment systems, which are more than the sum of their parts , In the human-environment system, the impacts are not unidirectional but reciprocal.

    For example, the environmental change impacts on morbidity and mortality are a growing area of interest, and some have sought to close the circle by looking at how environmentally induced mortality may affect population projections 2. There is also growing research on the health impacts of landscape or climatic changes on humans, in the one instance through the creation of mosquito breeding habitats that contribute to malaria , and in the other through heat stress or famine Research on the human-environment system also takes advantage of new data sources remote sensing, biophysical data, as well as georeferenced household surveys , new technologies high-powered computers, geographic information systems, spatial statistics , and new models agent-based, multilevel, and spatially explicit modeling.

    Population and Environment

    Much of the research reviewed in this chapter has sought to deconstruct population into its component parts and to understand how human social institutions in all their complexity e. Thus, they could be said to fit into this growing understanding of the human-environment system. Much population-environment research, whether at the local or global scales, is motivated by a broader concern for sustainability. Underlying some of the research, and contributing to some of the controversy, has been a concern for distributional justice in two forms: Whether research proves that population dynamics have a dominant or negligible effect on environmental outcomes in each of the domains we surveyed, it is still left to human societies to address these inequities in consumption and costs as well as to seek long-term solutions.

    Here, research on culture, consumption, values, institutions, and alternative industrial and food systems will add to what is known about the demographic dimension as societies seek to transition to sustainable systems 10 , Although we have sought to objectively review the literature rather than take a normative stance concerning the environmental impacts associated with population dynamics, at the global scale there is no question that humanity faces significant challenges in the coming decades owing to the scale and pace of changes in human numbers, population distribution, and consumption patterns.

    A challenge for micro- and mesoscale researchers is to understand how changes at the local and national scale relate to global-scale changes and how, in turn, their research can inform policies and programs at these lower scales that will attenuate environmental impacts at all levels. The views expressed here are those of the authors and not necessarily those of the sponsoring and supporting organizations. Fertility has declined significantly since the middle of the twentieth century in many developing countries owing to many factors, such as urbanization, the improved status of women through education and job opportunities, and increasing access to contraception.

    The different projections make different assumptions concerning future progress in reducing fertility. Yet Preston shows that the logical fallacy behind this by pointing out that most of the growth in fossil fuel use during this period was in developed countries with limited population growth and that population grew much faster in countries with the lowest per capita emissions.

    The remaining energy supply Variations in the roles of women around the world … admirably exemplify this diversity. Sustainability values, attitudes, and behaviors: Eakin H, Luers AL. Assessing the vulnerability of social-environmental systems. McGranahan G, Satterthwaite D. Dynamics of land-use and land-cover change in tropical regions. Queries on the human use of the Earth. The authors are not aware of any biases that might be perceived as affecting the objectivity of this review. National Center for Biotechnology Information , U. Annu Rev Environ Resour.

    Author manuscript; available in PMC Dec See other articles in PMC that cite the published article. Abstract The interactions between human population dynamics and the environment have often been viewed mechanistically. We now turn to a review of the five issue areas. Land-Cover Change and Deforestation The conversion of natural lands to croplands, pastures, urban areas, reservoirs, and other anthropogenic landscapes represents the most visible and pervasive form of human impact on the environment Open in a separate window.

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    Agricultural Land Degradation or Improvement Land-cover change research also considers changes in the quality of land resources as a result of human uses, which is the focus of this section. Abstraction and Pollution of Water Resources The water cycle ties together life processes. Coastal and Marine Environments From the earliest times, the preponderance of global economic activity has been concentrated in the coastal zone 92 , with settlements often growing on the continental margins to take advantage of overseas trade and easy access to the resources of the rural hinterlands.

    Population and Environment

    Energy, Air Pollution, and Climate Change Even when they are connected to the electric grid, some two billion poor people in the developing world still largely rely on biomass to meet their energy needs. Recent research has illuminated the ways in which a number of population variables—age and sex composition, household demographics, and the elements of the population balancing equation fertility, mortality and migration —are related to environmental change. Most demographers and many other social scientists subscribe to a mediating variable theory, which states that population dynamics affect the environment through other variables such as culture, consumption levels, institutions, and technology.

    Across the environmental issues covered in our review, population dynamics usually act in concert with other significant factors such as local institutions, policies, markets, and cultural change. Teasing out the relative contribution of each factor can often be difficult. The scale of analysis can significantly affect findings concerning the role of population dynamics in environmental change.

    Both freshwater resources and coastal and marine ecosystems are often managed as common property resources CPRs ; hence levels of resource degradation or depletion depend more on the existence of effective management systems than on population variables per se. In research on population and energy use, the household has been found to be a more useful unit of analysis than the individual, and population-environment researchers have made major strides in understanding how household size, composition, and income are related via energy use to environmental impacts.

    Emerging understanding of complex human-environment systems is informing work in the area of population and the environment, and vice versa. FUTURE ISSUES Greater exploration of the linkages between micro- farm or household level and macroscale global processes manifested at meso- subnational scales in population-environment research across the different issue areas is needed. Careful microscale longitudinal studies measuring population variables, household consumption, biophysical variables, institutional arrangements, and technologies employed over time should be conducted.

    Given the environmental footprints of urban areas on rural hinterlands, one unresolved issue relates to the impact of population spatial distribution. For example, what would environmental impacts be if the same population were spread more evenly across the landscape rather than concentrated in urban areas? Population-environment researchers could contribute to better understanding current consumption levels and the effects of future aspirations of the growing middle classes of Asia and Latin America as they relate to the sustainability transition.

    A new generation of IPAT modeling is needed that explicitly accounts for the interactions among the IPAT terms, including the reciprocal impacts of environmental changes on population dynamics, and that is made part of integrated assessment modeling. Future research could explore the increase in human mobility and collapse of geographical space as it affects population-environment relationships. Footnotes 1 Fertility in most of the developed world is at or below replacement levels 2. More people, more fallow: More People Less Erosion: Environmental Recovery in Kenya. The Growth of World Population.

    The Limits to Growth: Curran S, de Sherbinin A. Driving the human ecological footprint. The Revision Highlights. United Nations Millennium Declaration. Changes in ecosystem services and their drivers across the scenarios. Ecosystems and Human Well-being: A Compendium of Data on Global Change. The Living Planet Report Impact of population growth. Analytic tools for unpacking the driving forces of environmental impacts.

    On defining the problem of population and environment. The Conditions of Agricultural Growth. This landmark work explores the conditions under which agricultural intensification is likely to take place. People, Resources, Environment, and Immigration. Four theories of population change and the environment.

    A geographical perspective on poverty-environment interactions. Debates on population and the environment; Popul.

    Population and development within the ecophere: Population, poverty, and the local environment. Population and Climate Change.

    This is one of the most comprehensive works to date on the subject of population and climate change. Caldwell JC, Caldwell P. The cultural context of high fertility in sub-Saharan Africa. She concludes by calling for policymakers to pay increased attention to the role of population and forsake the search for one-step solutions to environmental problems. Example 2 the Aral Sea Basin. Example 4 Energy Policy in India. Consequences of Climate Change. Consequences of LandUse Change. Land-use Change in the Northwestern Uplands of Vietnam: