Population-environment theory and contemporary applications
Humans have sought to understand the relationship between population dynamics and the environment since the earliest times (1-3), but it was Thomas Malthus’ Essay on the Principle of Population in 1798 that is credited with launching the study of population and resources as a scientific topic of inquiry. Malthus’ famous hypothesis was that population numbers tend to grow exponentially while food production grows linearly, never quite keeping pace with population and thus resulting in natural “checks” (such as famine) to further growth. Although the subject was periodically taken up again in the ensuring decades, it wasn’t until the 1960s that significant research interest was rekindled. In 1963 the U.S. National Academy of Sciences published The Growth of World Population, a report that reflected scientific concern about the consequences of global population growth, which was then reaching its peak annual rate of two percent. In 1968, Paul Ehrlich published The Population Bomb, which focused public attention on the issue of population growth, food production and the environment. By 1972 the Club of Rome had released its World Model, which represented the first computer-based population-environment modeling effort, predicting an “overshoot” of global carrying capacity within 100 years (4).
Efforts to understand the relationship between demographic and environmental change are part of an ongoing tradition, yet it is a tradition that has often sought to reduce environmental change to a mere function of population size or growth. While we start from the premise that population dynamics do indeed have an impact on the environment, we also believe that explanations of environmental change that give a pre-eminent place to population size and over-simplify a complex reality often raise more questions than they answer, and may in some instances even provide the wrong answers.
As the field of population-environment studies has matured, researchers increasingly want to understand the nuances of the relationship. In the past two decades demographers, geographers, anthropologists, economists, and environmental scientists have sought to answer a more complex set of questions, which include among others:
- How do specific population changes (in density, composition, or numbers) relate to specific changes in the environment (such as deforestation, climate change, or ambient concentrations of air and water pollutants)?
- How do environmental conditions and changes, in turn, affect population dynamics?
- How do intervening variables, like institutions or markets, mediate the relationship?
- And how do these relationships vary in time and space?
They have sought to answer these questions armed with a host of new tools (geographic information systems, remote sensing, computer-based models, and statistical packages) and evolving theories on human-environment interactions.
This article explores the ways in which demographers and other social scientists have sought to understand the relationships among a full range of population dynamics (e.g. population size, growth, density, age and sex composition, migration, urbanization, vital rates) and environmental changes. While per capita environmental impacts are far greater in the developed world, the emphasis of this article is largely on the developing world because this is where much of the micro- and meso-level research has focused (5).
The article begins with a short review of the theories for understanding population and the environment. It then proceeds to provide a review of studies that have examined population dynamics and their relationship to the following environmental issue areas:
- land-cover change and deforestation
- agricultural land degradation and improvement
- abstraction and pollution of water resources
- coastal and marine environments
- and energy, air pollution, and climate change
In the concluding section we relate population-environment research to the emerging understanding of complex human-environment environment systems.
A wide array of theories have emerged to describe the population environment relationship, each theory leading to different conclusions and policy recommendations. Here we review the most prominent theories in the field of population and environment.
The introduction briefly touched on the work of Malthus, whose theory still generates strong reactions 200 years after it was first published. Adherents of Malthus have generally been termed neo-Malthusians. In its simplest form, neo-Malthusianism holds that human populations, because of their tendency to increase exponentially if fertility is unchecked, will ultimately outstrip the earth’s resources, leading to ecological catastrophe. This has been one of the dominant paradigms in the field of population and the environment, but many social scientists reject it because of its underlying biological/ecological underpinnings, treating humans in an undifferentiated way from other species that grow beyond the local “carrying capacity.” Malthusianism has been criticized for overlooking cultural adaptation, technological developments, trade, and institutional arrangements that have allowed human populations to grow beyond their local subsistence base.
|For Malthus, as population increases exponentially and food production only linearly, a point where food supply is inadequate will at some point be reached. (via Wikimedia Commons)|
The so-called Boserupian hypothesis, named after agricultural economist Esther Boserup, holds that agricultural production increases with population growth due to the intensification of production (greater labor and capital inputs). Although often depicted as being in opposition to Malthusianism, Malthus himself acknowledged that agricultural output increases with increasing population density (just not fast enough), and Boserup acknowledged that there are situations under which intensification might not take place (6-7). As Turner and Ali (8) point out, the main difference between the theories of Malthus and Boserup is that Malthus saw technology as being exogenous to the population-resource condition, and Boserup sees it as endogenous. Cornucopian theories espoused by some neoclassical economists stand in sharper contrast to neo-Malthunisianism because they posit that human ingenuity (through the increased the supply of more creative people) and market substitution (as certain resources become scarce) will avert future resource crises (9-10).
Political ecology also informs the population-environment literature (11-12). Many political ecologists see population and environment as linked only insofar as they have a common root cause, poverty, and that poverty itself stems from economic imbalances between the developed and developing world and within developing countries themselves (e.g., 13-14). A number of theories such as the intermediate variable theory (11-12) or the holistic approach theory (15), which are often subscribed to by demographers, state that population is one of a number of variables that affect the environment, and that rapid population growth simply exacerbates other conditions such as bad governance, civil conflict, wars, polluting technologies, or distortionary policies.
Some theories relating to population and environment are built on theoretical contributions from a number of fields. A case in point is the vicious circle model (VCM), which attempts to explain sustained high fertility in the face of declining environmental resources (16-18). In this model, it is hypothesized that there are a number of positive feedback loops that contribute to a “downward spiral” of population growth, resource depletion, and rising poverty (see land degradation section) (19-22).
It is important to note that these theories may simultaneously operate at different scales, and thus all could conceivably be correct. Theoretical frameworks can be important guides to action: a good theory helps to develop well-targeted policies, however, bad theory can become the “orthodoxies” underlying government and development agency policies and programs that are very difficult to overcome (23-24). Each of the above theories identifies one or more ultimate causes for environmental degradation, which if remedied, would “solve” the problem. Unfortunately, many theories in the realm of population and the environment have not been subjected to rigorous empirical testing to allow them to be categorized as robust. This is partly because the linkages are complex and difficult to disentangle. Fortunately for the field as a whole, the picture is beginning to change and a number of studies at the micro-level have used robust statistical methods and multi-level modeling in order to test theories such as the vicious circle model (25-26).
Reviews by Environmental Issue Area
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 (27). Today, roughly 40% of the Earth’s land surface is under agriculture, and 85% has some level of anthropogenic influence (28). While the world’s population is now 50% urban, urban areas occupy less than three percent of the Earth’s surface (29). We can conclude from this that large-scale land cover change is largely a rural phenomenon, though many of its drivers can be traced to the consumption demands of the swelling urban middle classes (30-31).
|Deforestation in Amazonia. The roads in the forest follow a typical "fishbone" pattern. (Image by NASA, via Wikimedia Commons)|
Most developed countries largely deforested their lands in past centuries, so today most land conversion from natural states to human uses is occurring in the developing world, particularly in the tropics through forest conversion to agriculture (32).[i] Given the scale of these transformations and their intimate but complex linkages with population dynamics, research on land use/cover change (LUCC) and particularly deforestation constitutes a large portion of the population-environment literature. Demographic variables are linked at different scales to this phenomenon (33). In this section we briefly outline how population dynamics affect LUCC through changes in fertility, population structure, and migration, and how these interactions are largely mediated by scale. We also reference case studies illustrating the sometimes counter-intuitive relationship between population variables and LUCC.
In much of the developing world fertility rates are plummeting, especially in urban areas. Conversely, the regions of highest fertility are often in the most remotely settled lands where the agricultural frontier continues to advance. These areas tend to be both biodiverse and ecologically sensitive, and high fertility and associated rapid population growth directly contribute to land conversion in these forest frontier areas (34-40).
Despite the high fertility of remote rural populations, migration remains the primary source of population growth in forest frontiers and is a necessary precedent to frontier deforestation in the forest transitions causal chain (41-42). 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 (43-44).
Population dynamics are central to LUCC, but population exerts its influence synergistically with other factors. Demand for agricultural land among small holders directly impacts forest conversion while, through market forces, urban and international demand for forest and agricultural products further contribute to LUCC through logging and large-scale agriculture (45). Political and institutional factors also play an important role in shaping LUCC. For example, government investments in roads, subsidies to the agricultural sector, or policy with regards to land tenure can directly influence deforestation rates. Such effects are well researched in the Brazilian Amazon (46-49). Cultural preferences can also affect LUCC, such as the desire for cattle as a status symbol among Central American frontier farmers (50-51). Such intervening variables help explain inconsistencies in population-LUCC dynamics (52).
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 (52). Examples of this are evident in the literature for Latin America where many nations have experienced declining rural populations but continued deforestation (37). A dramatic example is Ecuador whose Amazon region’s forest canopy is facing rapid attrition to growing settlements of frontier farmers while overall rural population is declining due to falling fertility and rapid urbanization (53-54). This apparent anomaly is explained by the fact that the small populations moving to forest frontiers, while accounting for a minority of a nation’s rural population, contribute a disproportionate amount to the nation’s total deforestation. In parts of the Brazilian Amazon, forest conversion has been driven increasingly by exogenous factors, such as global demand for soybeans, and owing to increasingly mechanized farming the region has also experienced rural population decline (55).
Land cover dynamics are the most evident mark of human occupation of the 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.g., at what spatial and temporal scales does population interact with political, economic, and social processes to produce LUCC?). A challenge for future research will be to disentangle the contributions of population and other dynamics across spatial and temporal scales through a diversity of research methods and better data at the meso-scale.
Agricultural land degradation or improvement
Land-cover change research also considers changes in land cover types, and quality of those 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 land degradation or improvement and increasing population density in subsistence agricultural areas (56). This is in part due to widely differing estimates regarding the extent of land degradation, with global estimates ranging from 20 to 51 million sq. km (57). This section considers arguments and evidence marshaled by two major schools of thought: “vicious circle” proponents who believe that increasing population density in the context of high poverty almost inevitably leads to land degradation, and the so-called “Boserupians” who suggest that increasing density leads to intensification of agricultural systems such that yields per unit area (and per capita) are increased.
|Yuma Arizona (NASA/terraprints.com, via Wikimedia Commons)|
Economists have been among the major proponents of the VCM. For example, Panayotou (58) and Dasgupta (16, 59) have suggested that children are valued by rural households in part because they transform open access resources (forests, fisheries, and rangeland) into household wealth, resulting in the “externalization” of the costs of high fertility. One manifestation is the process of “extensification,” whereby farm households in frontier areas use additional labor to open up new lands for cultivation (60). 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.
Testing of the VCM is difficult, however, since one is searching for a relatively small “resources effect” on fertility when there are at least a score of potentially confounding variables, and testing the direction of causality requires time series data on social and environmental variables, which is quite rare. Economists Filmer and Pritchett (61) found qualified support for the vicious circle hypothesis using detailed data from Pakistan on child time use, firewood collection activities, and recent fertility. However, they could not establish a “fertility effect” on resource or land degradation. Pascual and Barbier’s (62) modeling of shifting cultivation in the Yucatan found that among poor households, as population density increased the response was to further extensify or reduce fallow periods, whereas among better off households labor was shifted to off-farm employment. Thus, though anecdotal evidence is abundant and development policymaking 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. (63) examined changes in population density and agricultural productivity in Machakos District, Kenya. This study confirms the basic Boserupian hypothesis: increased food demand, a denser network of social and market interactions, labor intensive agriculture and economies of scale helped to avert a “Malthusian crisis.” Yet even in this “text book” study, other researchers working in the district found important social differentiation in livelihood improvements, land alienation, and government limitations on mobility – elements that tend to mar the otherwise rosy picture (64).
Mortimore (65) found similar “success stories” in three dryland areas of West Africa where some common ingredients were found that resulted in improved or stable soil fertility and yields despite rapid population growth and high densities. The author 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.
In Asia, there have also been successes, thanks largely to success of the “green revolution”, a package of improved seeds and agricultural inputs that resulted in higher yields (66). Turner & Shajaat Ali (8) studied time series data (1950-1986) for 265 households in six villages in Bangladesh. They found support for the induced intensification hypothesis, with yields largely keeping pace with or exceeding population growth despite high population densities (783 persons per km2). 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 land holdings), 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, as evidenced by this recent study in China (67).
Although population can perhaps be discounted as the only relevant variable, there is little doubt that rapid population growth in poor rural areas can be a complicating factor in the pursuit of sustainable land use, especially since policies and markets are rarely aligned in such a way as to produce the most favorable results. One important advance for studies in this area will be the development of better maps of soil quality and land degradation with the aid of remote sensing and local soil samples, since at least part of the debate over population’s impact can be explained by differing interpretations of what constitutes “degradation” and a paucity of empirical evidence for the relationship.
Abstraction and pollution of water resources
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. At the global level irrigation water for agriculture is the biggest single user (about 70% of water use), followed by industry (23%) and domestic uses (8%) (68). If “green water” is added to the mix (water that feeds rainfed crops), then crop production far and away outstrips other water uses. As demand for food increases with growing populations and changing tastes (including growing demand for animal vs. 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 with many other African countries expected to follow (69).
Studies at the local level, as with other population-environment dynamics, reveal a varied picture. A number of local studies found that community involvement in water management institutions, appropriate technologies, and the respect for the human right for water could all help to meet human needs (70). Top-down management and large hydro-electric projects were often associated with negative impacts on communities dependent on aquatic ecosystems. 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 (71). 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 (72). 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.
Researchers in densely populated Sao Paulo State in Brazil examined water resources in the Piracicaba and Capivari River Basins (PCB) within the Campinas Administrative Region (AR) (73). Campinas is Brazil's 14th largest city, as well as its third largest industrial center, and an important agricultural region as well. 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, since the rapidity and low density of growth meant that water supply and sanitation infrastructure could not keep up. 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 wastewaters.
In summary, as in other areas the relationship between population dynamics and water resources is complex. At the aggregate level, and other things being equal, population growth most assuredly does reduce per capita water availability. It is in this light that the Global International Waters Assessment listed population growth first in a series of root causes of the “global water crisis” (74). 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.
Coastal and marine environments
From the earliest times the preponderance of global economic activity has been concentrated in the coastal zone (75), 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 (76). Today, 10% of the world’s population lives at less than ten meters above sea level (even though this area only accounts for 2.2% of the world’s land area) and coastal zones have higher population densities than any other ecologically defined zone in the world (29, 77). Coastal and marine environments are very important for human health and well-being, and they are also quite vulnerable to anthropogenic impacts. Yet, until recently most population-environment research has focused on terrestrial ecosystems, possibly because the human “footprint” on coastal and marine ecosystems is harder to discern.
Not surprisingly, over half of the world’s coastlines are at significant risk from development-related activities (78), and the potential (and realized) environmental damage is substantial. Population growth is often named as the driver of coastal and marine environmental problems, while proximate causes can be traced to specific practices (79). 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 (80). Besides 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. Although listed as a driver, 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.
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 (81-82). 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 in Brazil (83) and the Galapagos (84) respectively has hypothesized that migrants misuse resource extraction technologies which leads to environmental degradation (85). In both cases the results seem to be a function of the migrants’ limited local knowledge as well as expansionist attitudes and short-term time horizons for profiting from the extraction of coastal and marine resources.
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 (86). 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 (87-89).
Human impacts on coastal and marine environments are not a simple function of population size or density. Nonetheless, coastal and marine environments continue to be among the most threatened ecosystems in the world, due in part to the sheer scale of detrimental human activities associated with urbanization along the coasts, high population density, and a growing tourist market.
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 since environmental boundaries are fluid. Also important is the impact of local and global consumption on marine and coastal environments. Further research is needed to assess how population-environment linkages in marine and coastal areas are influenced by global food trade connecting consumers and producers from opposite sides of the world.
Energy, air pollution and climate change
More than 80% of global energy consumption is derived from fossil fuels (90), and it is this dependence on fossil energy that is responsible for the release of the greenhouse gases and airborne pollutants that are altering atmospheric composition and processes on a global scale. 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 U.S. is 48 times what it is in Bangladesh and 4.7 times the world average), it would be wrong to suggest that population variables are irrelevant. Hence we review a number of empirical studies that examine population-energy linkages in a systematic and quantitative manner.[ii]
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, since 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 (17, 91). In a pioneering study, MacKellar et al. (92) found that because growth in the number of households outpaces population growth due to trends in fertility, divorce and ageing; using household numbers as the demographic unit of analysis, changes in demographic factors accounted for 41% of the total increase in energy consumption of the industrialized countries during 1970-1990, whereas using population growth as the demographic unit of analysis, changes in demographic factors accounted for only 18%. 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.
In studying demographic impacts (via energy consumption) on air pollution, scientists have identified a number of important factors that jointly determine pollutant emissions, including population, affluence, and technology (93-94). Selden et al. (95) analyzed the reduction of U.S. major air pollution emissions from 1970 to 1990 and found that changes in economic scale, economic composition, energy mix, energy intensity and emissions intensity all played important roles. 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. The different patterns of impacts may reflect the nature of complicated interactions between different pollutants and regional geographic/climatic conditions (96-98), income, and technological levels (99-100).
Due to the complexity of population interactions as well as political issues, population issues were not considered in formulation of the Kyoto Protocol (101) and have also been largely excluded from the IPCC’s assessment reports (102), though population projections are an important part of the Special Report on Emissions Scenarios (SRES) (103). However, along with downshifting population growth rate, assumptions on economic growth and technological changes in the new scenario are accordingly adjusted, reflecting a moderate demographic impact on GHGs emission (104). 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. In the new run of socioeconomic scenarios for climate change research communities the Shared Socioeconomic Pathways (SSPs, 105), it considers demographic factors much beyond population size, including key elements such as changes in age structure, urbanization and education attainment (106).
Simultaneous and consistent projections of population, urbanization, and households is a challenging demographic task (107-108). Dalton et al. (109) introduced heterogeneous households into a general equilibrium PET (population- environment-technology) model of the U.S. economy by incorporating them into cohorts by age groups (or “dynasties”). These dynamics and other relationships implied by household projections create non-linear interacting effects that influence each dynasty’s future saving and consumption decisions. Their research shows that including age heterogeneity among U.S. households reduces emissions by almost 40% in the low population scenarios by year 2050, and effects of aging on emission can be as large as, or larger than, effects of technical change in some cases. Those effects are believed to be much larger for the developing world, such as was recently shown for India and China by O’Neil et al. (110), 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 (111), 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.[iii] This makes human societies at once messy for modeling and fascinating to study. The new understanding builds on the concept of coupled human-environment systems which are more than the sum of their parts (112-113).
In the human-environment system, the impacts are not uni-directional 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 (114), and in the other through heat stress or famine (115). 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, GIS, spatial statistics), and new models (agent-based, multi-level, and spatially explicit modeling). Much of the research reviewed in this article has sought to deconstruct “population” into its component parts, and to understand how human social institutions in all their complexity (e.g. markets, policies, communities) mediate the impact of population variables on the use of resources, waste generation, and environmental impacts. 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 senses: that the 6 billion citizens of developing countries might be able to raise their living standards and hence their consumption levels from their previously low levels, and that the costs of biodiversity conservation and environmental protection not be unfairly borne by the poorest (116). 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, and 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 (117-118).
- Petersen, W. (1972). Readings in population. New York: Macmillan.
- Cohen, J. E. (1995). How many people can the earth support?. The Sciences,35(6), 18-23.
- Livi-Bacci, M. (2012). A concise history of world population. John Wiley & Sons.
- Meadows, D. H., Meadows, D., Randers, J., & Behrens III, W. W. (1972). The Limits to Growth: A Report for the Club of Rome’s Project on the Predicament of Mankind (New York: Universe).
- An, L., D. López-Carr (2012). Modeling Coupled Human-Natural Systems: Research Directions. Ecological Modeling. (229)1-4.
- Boserup, E. (1965). The conditions of agricultural growth. Earthscan, London.
- Curran, S. R., & de Sherbinin, A. (2004). Completing the picture: the challenges of bringing “consumption” into the population–environment equation. Population and Environment, 26(2), 107-131.
- Turner, B. L., & Ali, A. S. (1996). Induced intensification: agricultural change in Bangladesh with implications for Malthus and Boserup. Proceedings of the National Academy of Sciences, 93(25), 14984-14991.
- Simon, J. L. (Ed.). (1990). Population matters: People, resources, environment, and immigration. Transaction publishers.
- Aligica, P. D. (2009). Julian Simon and the “Limits to Growth” Neo-Malthusianism. The Electronic Journal of Sustainable Development, 1(3), 49.
- Jolly, M. C. L. (1994). Four theories of population change and the environment.Population and Environment, 16(1), 61-90.
- Hummel, D., Adamo, S., de Sherbinin, A., Murphy, L., Aggarwal, R., Zulu, L., ... & Knight, K. (2013). Inter-and transdisciplinary approaches to population–environment research for sustainability aims: a review and appraisal.Population and Environment, 34(4), 481-509.
- Gray, L. C., & Moseley, W. G. (2005). A geographical perspective on poverty–environment interactions. The Geographical Journal, 171(1), 9-23.
- Swyngedouw, E. (2009). The Political Economy and Political Ecology of the Hydro‐Social Cycle. Journal of Contemporary Water Research & Education,142(1), 56-60.
- Chi, G. 2005. “Debates on population and the environment.” Contribution to the Population-Environment Research Network (PERN) cyberseminar on Population and MDG-7, 5-16 September 2005.
- Dasgupta, P. S. (1995). Population, poverty and the local environment. Beijer International Institute of Ecological Economics.
- O'Neill, B. C., MacKellar, F. L., & Lutz, W. (2005). Population and climate change. Cambridge University Press.
- Bremner, J., Lopez-Carr, D., Suter, L., & Davis, J. (2010). Population, poverty, environment, and climate dynamics in the developing world. Interdisciplinary Environmental Review, 11(2), 112-126.
- Caldwell, J. C., & Caldwell, P. (1987). The cultural context of high fertility in sub-Saharan Africa. Population and development review, 409-437.
- Cain, M. (1983). Fertility as an adjustment to risk. Population and Development Review, 688-702.
- Hardin, G. (1968). The tragedy of the commons. science, 162(3859), 1243-1248.
- Atiqul Haq, S. M., Vanwing, T., & Hens, L. (2010). Perception, Environmental Degradation and Family Size Preference: a Context of Developing Countries.Journal of Sustainable Development, 3(4).
- Batterbury, S., Forsyth, T., & Thomson, K. (1997). Environmental transformations in developing countries: hybrid research and democratic policy.Geographical Journal, 163(2), 126-132.
- Leach, M., & Mearns, R. (1996). The Lie of the Land: challenging received wisdom on the African environment. James Currey Ltd.
- De Sherbinin, A. (2006). Rural household micro-demographics, livelihoods and the environment. Background paper, Population-Environment Research Network Cyberseminar, 10-24.
- An, L., & Liu, J. (2010). Long-term effects of family planning and other determinants of fertility on population and environment: agent-based modeling evidence from Wolong Nature Reserve, China. Population and Environment,31(6), 427-459.
Land Cover Change and Deforestation
- Turner, B. L. (Ed.). (1990). The earth as transformed by human action: global and regional changes in the biosphere over the past 300 years. CUP Archive.
- Sanderson, E. W., Jaiteh, M., Levy, M. A., Redford, K. H., Wannebo, A. V., & Woolmer, G. (2002). The Human Footprint and the Last of the Wild. BioScience, 52(10), 891-904.
- McGranahan G, Marcotullio PJ, Bai X, et al. 2005. Urban Systems. In Ecosystems and Human Well-Being: Current Status and Trends, ed. R Hassan, R Scholes, N Ash. Washington D.C.: Island Press.
- Carr, D. L. (2004). Tropical deforestation. In WorldMinds: Geographical Perspectives on 100 Problems (pp. 293-298). Springer Netherlands.
- DeFries, R. S., Rudel, T., Uriarte, M., & Hansen, M. (2010). Deforestation driven by urban population growth and agricultural trade in the twenty-first century. Nature Geoscience, 3(3), 178-181.
- López-Carr, D., & Burgdorfer, J. (2013). Deforestation drivers: population, migration, and tropical land use. Environment: Science and Policy for Sustainable Development, 55(1), 3-11.
- Carr, D. L., & Bilsborrow, R. E. (2001). Population and land use/cover change: A regional comparison between Central America and South America. Journal of Geography Education, 43(8), 7-16.
- Knodel, J. E. (1987). Thailand's reproductive revolution: Rapid fertility decline in a third-world setting. Univ of Wisconsin Press.
- Stokes, C. S., & Schutjer, W. A. (1984). Access to land and fertility in developing countries.
- Singh, S., Casterline, J. B., & Cleland, J. G. (1985). The proximate determinants of fertility: Sub-national variations. Population Studies, 39(1), 113-135.
- Carr, D. L. (2005). Population, land use, and deforestation in the Sierra de Lacandón National Park, Petén, Guatemala. The Professional Geographer,57(2), 157-168.
- Rosero-Bixby, L., & Palloni, A. (1998). Population and deforestation in Costa Rica. Population and Environment, 20(2), 149-185.
- Rudel, T. K., & Horowitz, B. (2013). Tropical Deforestation: Small Farmers and Land Clearing in Ecuadorian Amazon. Columbia University Press.
- Pichón, F. J. (1997). Colonist Land‐Allocation Decisions, Land Use, and Deforestation in the Ecuadorian Amazon Frontier. Economic Development and Cultural Change, 45(4), 707-744.
- Geist, H. J., & Lambin, E. F. (2001). What drives tropical deforestation. LUCC Report series, 4, 116.
- Carr, D. (2009). Population and deforestation: why rural migration matters.Progress in Human Geography, 33(3), 355-378.
- Barbieri, A. F., & Carr, D. L. (2005). Gender-specific out-migration, deforestation and urbanization in the Ecuadorian Amazon. Global and Planetary Change, 47(2), 99-110.
- Barbieri, A. F., Carr, D. L., & Bilsborrow, R. E. (2009). Migration within the frontier: the second generation colonization in the Ecuadorian Amazon.Population research and policy review, 28(3), 291-320.
- Richards, P. D., Myers, R. J., Swinton, S. M., & Walker, R. T. (2012). Exchange rates, soybean supply response, and deforestation in South America. Global Environmental Change, 22(2), 454-462.
- Alves, D. S. (2002). Space-time dynamics of deforestation in Brazilian Amazonia. International Journal of Remote Sensing, 23(14), 2903-2908.
- McCracken, S. D., Brondizio, E. S., Nelson, D., Moran, E. F., Siqueira, A. D., & Rodriguez-Pedraza, C. (1999). Remote sensing and GIS at farm property level: Demography and deforestation in the Brazilian Amazon. Photogrammetric Engineering and Remote Sensing, 65, 1311-1320.
- Pfaff, A. S. (1999). What drives deforestation in the Brazilian Amazon?: evidence from satellite and socioeconomic data. Journal of Environmental Economics and Management, 37(1), 26-43.
- Arima, E. Y., Richards, P., Walker, R., & Caldas, M. M. (2011). Statistical confirmation of indirect land use change in the Brazilian Amazon.Environmental Research Letters, 6(2), 024010.
- Carr, D. (2006). A tale of two roads: Land tenure, poverty, and politics on the Guatemalan frontier. Geoforum, 37(1), 94-103.
- Hoelle, J. (2011). Convergence on cattle: political ecology, social group perceptions, and socioeconomic relationships in Acre, Brazil. Culture, Agriculture, Food and Environment, 33(2), 95-106.
- Carr, D. L. (2002). The role of population change in land use and land cover change in rural Latin America: Uncovering local processes concealed by macro-level data. Land use changes in comparative perspective, 133-48.
- Pan, W. K., Walsh, S. J., Bilsborrow, R. E., Frizzelle, B. G., Erlien, C. M., & Baquero, F. (2004). Farm-level models of spatial patterns of land use and land cover dynamics in the Ecuadorian Amazon. Agriculture, Ecosystems & Environment, 101(2), 117-134.
- Rudel, T. K., & Horowitz, B. (2013). Tropical Deforestation: Small Farmers and Land Clearing in Ecuadorian Amazon. Columbia University Press.
- Hecht, S. B. (2005). Soybeans, development and conservation on the Amazon frontier. Development and Change, 36(2), 375-404.
Agricultural Land Degradation or Improvement
- Carr, D. L., Lopez, A. C., & Bilsborrow, R. E. (2009). The population, agriculture, and environment nexus in Latin America: country-level evidence from the latter half of the twentieth century. Population and Environment, 30(6), 222-246.
- Eswaran, H., Lal, R., & Reich, P. F. (2001). Land degradation: an overview.Responses to Land degradation, 20-35.
- Panayotou, T. (1994). The population environment and development nexus.
- Dasgupta, P. (2000). Population and resources: an exploration of reproductive and environmental externalities. Population and development Review, 26(4), 643-689.
- Bilsborrow, R. E., Ogendo, H. W., Pimentel, D., Mwaura, F., Moore, T. R., Rosenfield, A., ... & Davis, W. H. (1992). Population-driven changes in land use in developing countries. Ambio, 21(1), 37-45.
- Filmer, D., & Pritchett, L. H. (2002). Environmental degradation and the demand for children: searching for the vicious circle in Pakistan. Environment and Development Economics, 7(1), 123-146.
- Pascual, U., & Barbier, E. B. (2006). Deprived land‐use intensification in shifting cultivation: the population pressure hypothesis revisited. Agricultural Economics, 34(2), 155-165.
- Tiffen, M., Mortimore, M., Gichuki, F., Ahmad, A., Twumasi-Ankrah, K., Gianotten, V., ... & Ranis, G. (1995). More people less erosion: environmental recovery in Kenya. JOURNAL OF SOCIAL DEVELOPMENT IN AFRICA, 10(2), 366-78.
- Rocheleau D. 1995. More on Machakos. Environment 37(7): 3-5.
- Mortimore, M. (2005). Dryland development: success stories from West Africa.Environment: Science and Policy for Sustainable Development, 47(1), 8-21.
- Mishra, V. (2002). Population growth and intensification of land use in India.International Journal of Population Geography, 8(5), 365-383.
- Bai, Z., & Dent, D. (2009). Recent land degradation and improvement in China.AMBIO: A Journal of the Human Environment, 38(3), 150-156.
Abstraction and Pollution of Water Resources
- De Sherbinin, A. (1997). Water and population dynamics: local approaches to a global challenge. Population Reference Bureau.
- Engelman, R., & LeRoy, P. (1993). Sustaining water. Population and the future of renewable water supplies.
- De Sherbinin, A., Dompka, V., & Bromley, L. (1998). Water and population dynamics: case studies and policy implications.
- Zaba, B., & Madulu, N. (1998). A drop to drink? Population and water resources: illustrations from northern Tanzania.
- Mbonile, M. J. (2005). Migration and intensification of water conflicts in the Pangani Basin, Tanzania. Habitat International, 29(1), 41-67.
- Hogan, D. J., RODRIGUES, I., & CARMO, R. L. D. (1997). O Novo Padrão Migratório e os Impactos Sobre os Recursos Hídricos–As Bacias dos Rios Piracicaba e Capivari. Travessia, São Paulo, 10(28), 27-33.
- Global International Waters Assessment. (2006). Challenges to International Waters: Regional Assessments in a Global Perspective. UNEP/Earthprint.
Coastal and Marine Environments
- Sachs, J. D., Mellinger, A. D., & Gallup, J. L. (2001). The geography of poverty and wealth. Scientific American, 284(3), 70-75.
- Hinrichsen, D. (1997). Coastal waters of the world: trends, threats, and strategies. Island Press.
- McGranahan, G., Balk, D., & Anderson, B. (2007). The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones. Environment and Urbanization, 19(1), 17-37.
- Faye, M. L., McArthur, J. W., Sachs, J. D., & Snow, T. (2004). The challenges facing landlocked developing countries. Journal of Human Development, 5(1), 31-68.
- Bryant, D., Burke, L., McManus, J., & Spalding, M. (1998). Reefs at risk: a map-based indicator of threats to the worlds coral reefs.
- Guzman, H. M., Guevara, C., & Castillo, A. (2003). Natural disturbances and mining of Panamanian coral reefs by indigenous people. Conservation Biology,17(5), 1396-1401.
- Marquette, C. M., Koranteng, K. A., Overå, R., & Aryeetey, E. B. D. (2002). Small-scale fisheries, population dynamics, and resource use in Africa: the case of Moree, Ghana. AMBIO: A Journal of the Human Environment, 31(4), 324-336.
- Naylor, R. L., Bonine, K. M., Ewel, K. C., & Waguk, E. (2002). Migration, markets, and mangrove resource use on Kosrae, Federated States of Micronesia. AMBIO: A Journal of the Human Environment, 31(4), 340-350.
- Begossi, A. (1998). Resilience and neo-traditional populations: the caiçaras (Atlantic Forest) and caboclos (Amazon, Brazil). Linking social and ecological systems: management practices and social mechanisms for building resilience, 129-157.
- Bremner, J., & Perez, J. (2002). A case study of human migration and the sea cucumber crisis in the Galapagos Islands. Ambio: A Journal of the Human Environment, 31(4), 306-310.
- Perz, S. G. (2003). Social determinants and land use correlates of agricultural technology adoption in a forest frontier: A case study in the Brazilian Amazon.Human Ecology, 31(1), 133-165.
- Cassels, S., Curran, S. R., & Kramer, R. (2005). Do migrants degrade coastal environments? Migration, natural resource extraction and poverty in North Sulawesi, Indonesia. Human Ecology, 33(3), 329-363.
- Hanna, S.S. (2000). Managing for human and ecological context in the Maine soft shell clam fishery. Linking Social and Ecological Systems: Management Practices and Social Mechanisms for Building Resilience, 190.
- Hoffmann, T. C. (2002). Coral reef health and effects of socio-economic factors in Fiji and Cook Islands. Marine pollution bulletin, 44(11), 1281-1293.
- Palsson, G. (1998). Learning by fishing: practical engagement and environmental concerns (pp. 48-66). Cambridge, Cambridge University Press.
Energy, Air Pollution and Climate Change
- International Energy Agency (2006). World energy outlook. OECD/IEA.
- Ironmonger, D. S., Aitken, C. K., & Erbas, B. (1995). Economies of scale in energy use in adult-only households. Energy Economics, 17(4), 301-310.
- MacKellar, F. L., Lutz, W., Prinz, C., & Goujon, A. (1995). Population households and carbon dioxide emissions. Population and Development Review, 21(4), 849-65.
- Bongaarts, J. (1992). Population growth and global warming. population and Development Review, 299-319.
- O'Neill, B. C., Liddle, B., Jiang, L., Smith, K. R., Pachauri, S., Dalton, M., & Fuchs, R. (2012). Demographic change and carbon dioxide emissions. The Lancet, 380(9837), 157-164.
- Selden, T. M., Forrest, A. S., & Lockhart, J. E. (1999). Analyzing the reductions in US air pollution emissions: 1970 to 1990. Land Economics, 1-21.
- Neumayer, E. (2002). Can natural factors explain any cross-country differences in carbon dioxide emissions?. Energy Policy, 30(1), 7-12.
- Friedrichs, J., & Inderwildi, O. R. (2013). The carbon curse: Are fuel rich countries doomed to high CO2 intensities?. Energy Policy, 62, 1356-1365.
- Neumayer, E. (2004). National carbon dioxide emissions: geography matters. Area, 36(1), 33-40.
- Lantz, V., & Feng, Q. (2006). Assessing income, population, and technology impacts on CO2 emissions in Canada: Where's the EKC?.Ecological Economics, 57(2), 229-238.
- Huesemann, M. H. (2006). Can advances in science and technology prevent global warming?. Mitigation and Adaptation Strategies for Global Change, 11(3), 539-577
- Meyerson, F. A. (1998). Population, Carbon Emmissions, and Global Warming: The Forgotten Relationship at Kyoto. Population and Development Review, 115-130.
- Bongaarts, J., O’Neill, B. C., & Gaffin, S. R. (1997). Global warming policy: population left out in the cold. Environment, 39(9), 40-41.
- Nakicenovic, N., & Swart, R. (2000). Special report on emissions scenarios.Special Report on Emissions Scenarios, Edited by Nebojsa Nakicenovic and Robert Swart, pp. 612. ISBN 0521804930. Cambridge, UK: Cambridge University Press, July 2000., 1.
- O'Neill, B. C., Dalton, M., Fuchs, R., Jiang, L., Pachauri, S., & Zigova, K. (2010). Global demographic trends and future carbon emissions. Proceedings of the National Academy of Sciences, 107(41), 17521-17526.
- O’Neill, Brian C., Elmar Kriegler, Keywan Riahi, Kristie L. Ebi, Stephane Hallegatte, Timothy R. Carter, Ritu Mathur, and Detlef P. van Vuuren. "A new scenario framework for climate change research: the concept of shared socioeconomic pathways." Climatic Change (2013): 1-14.
- Jiang, Leiwen. 2014: Internal consistency of demographic assumptions in the shared socioeconomic pathways. Population and Environment. 35(3): 261-285.107 Jiang, Leiwen and Brian O’Neill, 2004: Towards a new model for probabilistic household forecasts, International Statistical Review, 72(1): 51-64.
- Jiang, Leiwen and Brian O’Neill, 2007: Impact of demographic trend on US household size and structure, Population and Development Review, 33 (3): 429-656.
- Jiang, L., & Hardee, K. (2011). How do recent population trends matter to climate change?. Population Research and Policy Review, 30(2), 287-312.
- Dalton, M., O'Neill, B., Prskawetz, A., Jiang, L., & Pitkin, J. (2008). Population aging and future carbon emissions in the United States. Energy economics,30(2), 642-675.
- O'Neill, B. C., Ren, X., Jiang, L., & Dalton, M. (2012). The effect of urbanization on energy use in India and China in the iPETS model. Energy Economics, 34, S339-S345.
- O’Neill, B. C., Balk, D., Brickman, M., & Ezra, M. (2001). A guide to global population projections. Demographic Research, 4(8), 203-288.
- An, L., He, G., Liang, Z., & Liu, J. (2006). Impacts of demographic and socioeconomic factors on spatio-temporal dynamics of panda habitat. InHuman Exploitation and Biodiversity Conservation (pp. 3-23). Springer Netherlands.
- Turner, B. L., Matson, P. A., McCarthy, J. J., Corell, R. W., Christensen, L., Eckley, N., ... & Tyler, N. (2003). Illustrating the coupled human–environment system for vulnerability analysis: three case studies. Proceedings of the National Academy of Sciences, 100(14), 8080-8085.
- Barbieri, A. F., & Soares-Filho, B. S. (2005). Population and land use effects on malaria prevalence in the southern Brazilian Amazon. Human Ecology,33(6), 847-874.
- Campbell-Lendrum, D., & Woodruff, R. (2006). Comparative risk assessment of the burden of disease from climate change. Environmental health perspectives,114(12), 1935.
- Walker, G. (2012). Environmental justice: concepts, evidence and politics. London: Routledge.
- Keyfitz, N. (1989). The growing human population. Scientific American, 261(3), 119-126.
- Curran, S. R., & de Sherbinin, A. (2004). Completing the picture: the challenges of bringing “consumption” into the population–environment equation. Population and Environment, 26(2), 107-131.
 This entry summarizes and updates work published in: de Sherbinin, A, D.L. Carr, S. Cassels, L. Jiang. (2007). Population and environment. Annual Review of Environmental Economics. 32(5):1-29.
[i] The Russian Far East is one of the few developed world regions with similarly high rates of conversion of primary forests, mostly due to logging and not to demand for agricultural lands.
[ii] Although there is extensive research on the reciprocal impact of air pollution and projected climate change on demographic variables such as morbidity, mortality, and migration this is beyond the scope of this review.