DEMOGRAPHY – Vol.

II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

POPULATION, NATURAL RESOURCES AND ENVIRONMENT

Haydea Izazola
Department of Methods and Systems. Universidad Autonoma Metropolitana-
Xochimilco, Mexico

Alan Jowett
Centro de Investigación y Docencia Económicas, Mexico

Keywords: Population dynamics, population-environment theory, food availability,

tropical deforestation, land-cover change, water resources, energy, emissions, climate
change, environmental migrants

Contents

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1. Introduction

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2. History of the debate
3. Contemporary approaches
4. Population and food availability
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5. Population and land use cover change
6. Population and water resources
7. Population, energy and climate change
8. Environmental migration
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9. Final remarks
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Acknowledgment
Glossary
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Bibliography
Biographical Sketches
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Summary
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Population-environment studies have implicitly permeated demography but only until

the mid-20th century has the debate been rekindled and research expanded. This article
reviews the origins and history of the population-environment debate and attempts to
provide insight into the most recent approaches and methodology. Beginning with the
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most traditional relationships established between demographic and environmental

dynamics, some of the most relevant relations and findings are presented and discussed.
This state-of-the-art revision is organized by some dimensions of these dynamics, and is
by no means exhaustive. The relationships between population and food availability,
land use, water resources, energy and climate change are some of the most visible and
studied within this emerging field of study. Some final methodological remarks and
suggestions for future research are outlined.

1. Introduction

Human populations have been forced to adapt to biological, economic and social
restrictions since the dawn of civilization and have transformed ecosystems to ensure
and enhance their survival. The 20th century witnessed two of the most profound social

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

and demographic changes in recorded history. On one hand, population rose from
around 1.6 billion in 1900 to over 6 billion in 2000. On the other, the transformation of
a considerable portion of natural ecosystems in order to accommodate and supply this
population grew accordingly in complexity and magnitude. Studying the relationship
among population, resources and the environment has been a challenge taken on by
various disciplines due its complexity, but also because of the controversy and
implications of the debate. Although population growth has been the most obvious
demographic trend in this relationship, urbanization, age and household structure,
poverty and migration are but a few of other demographic transformations essential to
understanding these interactions.

Biophysical research has established that since the end of the 18th century –but
especially since 1950- terrestrial and marine ecosystems have suffered profound
transformations. Atmospheric changes have been thoroughly documented as well. The

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conversion of practically unaltered ecosystems to cropland and the use of new
production technologies account for most of the transformation observed in terrestrial

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ecosystems. In marine environments, excessive fishing is pointed out as a direct driver
of recent transformation, while freshwater ecosystems have been profoundly affected by
changing water regimes and pollution. Nitrogen and phosphorus application directly
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related to human activities have generated clear environmental imbalances. Finally,
previous and ongoing climate change has been decisively linked to greenhouse gas
emissions. Ever-improving data availability and evidence of these changes have brought
population-environment studies to the forefront of academic debate, posing a challenge
within different disciplines but also among them; it is clear that biophysical sciences
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and social sciences must work together to better understand the challenges of
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environmental change and provide environmental- and human-friendly solutions to
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these problems.
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Demography has studied the population-environment relationship since its modern

origins, but started treating it as a specific field of study until the late 20th century. The
decades following the 1960’s observed an academic boom exploring and discussing this
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field, increasingly incorporating different demographic and ecological dimensions,

spatial and temporal scales and methodological approaches.

Given the predominance of quantitative approaches and the fact that they allow for
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descriptions, explanations and future projections, these studies can no doubt contribute
to reaching sustainable development. Most studies have focused on developing
countries mainly due to the relatively higher population growth rates and the diversity
of ecosystems found there, as well as the fact that the relationship between the two
dimensions is clearer than in developed countries.

2. History of the Debate

Optimum population levels and population growth have been noted and discussed since
ancient times. Cuneiform texts dating from 1600 BC already expressed concern about
excessive population. Confucius, Plato and Aristotle were known to discuss optimum
population in terms of governance, although population growth was widely regarded as
a positive trend. Roman and medieval policies that promoted population growth are well

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

documented. By the end of the 17th century, Dutch scientist Antoni van Leeuwenhoek
had estimated that the Earth’s land surface could support as much as 13.4 billion
inhabitants.

Throughout the 18th century, the debate concerning the sustainability of population
growth, most notably in terms of food requirements and their supply, was relatively
widespread, and several texts discussed the apparent incapacity of the Earth to produce
enough means of sustenance for an ever-increasing population.

It was not until Thomas Robert Malthus anonymously published his First Essay on
Population in 1798 that the debate became well-known and a primary concern for
several thinkers. Three elements that may have been crucial at making Malthus’ work
the best known concerning this subject are: the political-historical context at the time he
first published, the simplicity of his premises, and his ability to link it with the terms

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and debate of an up-and-coming discipline known as political economy. The French
Revolution had raised a number of questions and concerns linked to the new

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relationships between population and the distribution of wealth. Malthus’ theory
consisted of a simple syllogistic argument: food production grew arithmetically while
population grew geometrically, necessarily implying that the Earth’s capacity to feed
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this population would one day reach an end. Population increased when wages were
high, but this very increase eventually resulted in a reduction of wage levels. Whenever
population grew too large, wages fell below subsistence levels and extreme poverty
reduced population size. He later polished this theory to include the possibility of
workers restraining themselves from having too many children. Whether it was hunger,
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vice or family planning, population was kept below a certain level by these positive
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checks. The most important implications or corollaries of his theory were that of fixed
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per capita income, fixed land supply (and decreasing marginal productivity of this
factor) and little or scarce technological progress.
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Studies made in the late 20th century have pointed out that, ironically, the relationships
he established among population growth, income, and fertility rates seem to adequately
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fit data for several centuries, but were beginning to undergo transformations at the very
time he wrote and published his ideas. To Malthus’ credit, he lucidly pointed out
several demographic phenomena that have been retaken by several demographers,
namely migration as a resource to avoid positive checks and the influence of gender
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roles and woman subordination on fertility rates.

Karl Marx and Henry George are probably Malthus’ best-known 19th-century critics.
Marx mostly criticized the wording and epistemological implications of Malthus’
theory, denouncing the fact that poverty and misery were to be interpreted as a lack of
employment in the world of capital accumulation rather than an excess of low-income
population. Henry George on the other hand, together with many other American
thinkers who participated in the debate, pointed out that population was a driving force
of economic growth rather than a limitation. Regardless of these and other insightful
counterarguments, Malthus’ theory and implications thrived at an academic level during
a period which, in retrospect, would falsify them; the technological changes and
demographic transition that took place in Europe during the end of the 19th century and
beginning of the 20th have no doubt proved the specific implications and corollaries of

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

Malthus’ theory wrong.

The decades that followed World War II witnessed an unprecedented decrease in death
rates that were not accompanied by a drop in fertility rates in developing countries, in
contrast with what had occurred in Europe a century earlier. Late 20th-and early 21st-
century concern for environmental degradation and insufficiency of natural resources to
provide for an ever-growing population arose in the 1960’s mainly as a result of this
demographic transition gone awry. While D.O. Duncan’s POET model (Population,
Organization, Environment and Technology) redefined the conceptual framework of the
population-environment debate, most theories that followed tended either to side with
Malthusian views or oppose them, and only recently has the debate regained a certain
degree of neutrality in that respect that characterized Duncan’s ideas.

In The Conditions of Agricultural Growth, published in 1965, Danish agricultural

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economist Ester Boserup proposed a population-environment paradigm radically
different from that of Malthus: it was not agricultural production that limited population

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growth, but population growth and density that pressured agricultural production to
increase through technological change. This approach was not only the first coherent
academic counter-proposal to Malthus’ theory to be taken seriously, but was also highly
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compatible with neoclassical economics; the latter provided important theoretical
underpinnings for an integral Boserupian paradigm, including relative scarcity, prices,
markets and incentives for technological progress. In fact, modern development
economics would be unthinkable without Boserup’s arguments.
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The late 1960’s and the 1970’s, however, witnessed the peak of neo-Malthusianism
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when American ecologist Paul Ehrlich published The Population Bomb, followed by
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Dennis Meadows’ and the Club of Rome’s The Limits to Growth, which predicted
global collapse by 1985 and 2025, respectively. The latter employed a dynamic systems
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model with positive and negative feedback loops and interactions among five variables:
population, food production, natural resources, industrial output and pollution. The
model’s rigid assumptions and bleak forecast influenced public policy and promoted
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family planning in developing countries under the leadership of United Nations; the
1974 World Population Conference in Bucharest gave rise to national population
councils in several countries aimed at controlling or curbing fertility rates. The
demographic community in this context was limited to reporting on population
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dynamics and projecting possible population growth scenarios that focused on high
fertility rates in the developing world. The 1976 World Fertility Survey remains a
benchmark in demographic data compilation and research.

A Boserupian backlash soon followed; whereas Ehrlich and Meadows had presented
extremely pessimistic forecasts, Herman Kahn and Julian Simon responded with excess
optimism, for which they would be dubbed Cornucopians. Kahn et al. argued that
population growth would progressively decrease and that technological progress would
not only allow the Earth to sustain almost 15 billion inhabitants by the 22nd century, but
also raise world per capita income to unprecedented levels. Simon published The
Ultimate Resource in 1981 and is best-known for taking Boserup’s thesis to the
extreme; population growth increased human ingenuity for solving resource scarcity
and also represented a growing market for such solutions.

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

An alternative perspective inspired mostly by Marxist political economy, and

dependency theory, holds that the relationship between population and environment is
determined by historical and structural inequalities regarding control, access and use of
natural resources among and within countries.

3. Contemporary Approaches

Contemporary research on the population-environment relationship has addressed a

wide variety of demographic and ecological topics, and has been dominated by the
notion of sustainable development, namely the long-term capacity of meeting the needs
of present generations without compromising those of future generations. The most
influential demographic factors in this relationship are the population’s size, growth,
density, structure, distribution, consumption patterns and mobility at different levels of
aggregation and different spatial and temporal scales. The main environmental

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phenomena that interact with these demographic factors are land use cover change,
water resources and their availability, energy, climate change and natural or industrial

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disasters. Most population-environment literature has been concerned with the
influence of population over the environment, and only a smaller proportion has paid
significant attention to dynamic interactions. Previous reviews have organized literature
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on the subject following different criteria:

• The dominant theories that have attempted to study each topic (land use cover
change, water resources, etc.)
•
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The main methodological approaches

•
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The chronological sequence of research topics
• A combination of the above approaches
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Considering the diversity of topics, theories, and methodologies employed in this

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research, their systematization implies arbitrary decisions concerning the dimensions

and categories used to organize them, and –as other authors have recognized- most of
these categories are not mutually exclusive.
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While Malthus’ and Boserup’s original theories were linear and relatively simple,
subsequent research has proposed and delved into more complex relationships.
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The environmental Kuznets Curve, for instance, is an empirical relationship from which
many valid hypotheses have emerged. It outlines a non-linear relationship between
environmental impact and level of development that graphically resembles an inverted
U-shape; for low and high levels of development, environmental impact is relatively
low, while intermediate levels of development have higher impacts. Most theories that
use this concept as empirical support work under the assumption that at high
development levels, demand for environmental quality tends to increase, and there are
means and a willingness to pay in order to bring it about.

Theoretical and methodological progress –and progressively, data availability- in the

social sciences has allowed for different models that best explain population-
environment interactions. Below are listed and explained some of the most important or
elemental developments used to study these interactions.

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

The notion of human carrying capacity refers to an ecosystem’s capacity to sustain a

certain amount of population. Estimates of the Earth’s human carrying capacity depend
widely on the assumptions made by each model or study and have ranged from 2 billion
to 13 billion people in the literature. These exercises are essentially neo-Malthusian and
underlie a large portion of population-environment literature.

The concept of ecological footprint consists of transforming a nation’s consumption in

various categories (grain, meat, energy, etc.) into its equivalent in the land area
necessary for supplying this consumption and for absorbing its wastes. It shares an
important weakness with other approaches, as it does not consider the relationship
among population dynamics, economic development and technology. Its main virtue,
however, is its straightforwardness in pointing out the high ecological impact of cities
or countries that import resource-intensive products, deceitfully appearing to be low-
intensity polluters. Another criticism to this theory is that it may underline economic

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impact differentials among countries while underscoring said differentials within
countries.

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The development of statistical and econometric models has allowed studies to not only
incorporate correlations, but also improve specific discussions concerning causality,
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interactions (feedback loops in both ways), uncertainty and non-linearity among studied
variables and dynamics, significantly refining forecasting exercises. Data requirements
for these methods are particularly difficult to meet in developing countries, particularly
when dealing with environmental variables. It is essential to note that, when studying
relationships as complex and varying as population-environment interactions, statistical
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models cannot be relied upon to establish definitive causality. Also, the spatial scale and
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time span that are studied have important implications for the validity of assumptions
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and results. Institutional, qualitative and context-based approaches should not be

neglected as both an alternative and a complement to quantitative approaches.
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IPAT models consist of and receive their name from the equality I = P × A × T , where I
stands for environmental impact, P stands for population, A stands for affluence
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(output per capita), and T stands for technology (impact per unit of output). The model
dates back to a 1970’s debate in which Ehrlich took part. It has mainly been used for the
study of the impact of population growth on global emissions, but also for studying
other environmental factors like energy and fertilizer use. The model’s main virtue is its
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versatility, as replacing or further deconstructing the variables on the right-hand side of

the equation is relatively simple. IHAT models, in which population size and growth
are replaced by growth in the number and structure of households, have proven useful
as well.

STIRPAT models are based on the IPAT model but are essentially different, being
stochastic in nature and employing regression analysis. These models borrow heavily
from neoclassical production functions and offer an interesting and flexible approach to
population-environment studies. However, they should be treated with the same caution
as any other regression model. The selection of a functional form is for the most part
arbitrary and the assumptions of the model are far-fetched, particularly when dealing
with macro-level data. Even if a correct functional form existed and the assumptions of
the model were correct, the interpretation of the regression coefficients –the relevant

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

output of said models- remains ambiguous and subject to even more assumptions.
STIRPAT models represent the simplest econometric approach to P-E studies, and
represent a useful albeit naïve effort to quantify certain dimensions of this relationship.

General equilibrium models are also heavily influenced by neoclassical economics and
basically consist of equilibrium situations that, upon exogenous disturbances, reach a
different or the same equilibrium as a result of the interaction of its variables. These
models can incorporate specific structures and interactions of technology, markets or
other institutions. Thus, they allow for endogenizing population growth, technological
changes, and economic growth, among other phenomena. The complexity of these
models makes the discussion over functional form more specific and the interpretation
of regression coefficients more straightforward within a given approach. This very
complexity, however, requires very robust and precise data.

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Vicious circle models can be viewed as an amalgamation of general equilibrium models
in development economics and Garrett Hardin’s common goods paradigm. The latter

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states that, in the absence of clearly defined and enforced usage of common pool
resources –firewood, pasture, or fishing resources, for instance-, individual or
household decisions will tend to overexploit these resources. These models basically
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argue that, under certain conditions, high fertility, poverty and environmental
degradation are closely linked and can combine into a snowball effect of higher
population growth, increasing poverty and an ever-deteriorating environment. Drawing
heavily from vicious circle approaches, the PEDA model simulates and explores the
interactions among population changes, the environment, socioeconomic development
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and agriculture, and has been used in diverse contexts, predominantly in Africa. This
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model’s framework is solidly based on neoclassical growth theory and differs from
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vicious circle models due mainly to the thoroughness in its specification, innovation in
its selection of variables and the ambition of its scope. Unfortunately, due to the
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estimation method and under-identification of coefficients, several far-fetched

assumptions must be made in order to reach any conclusions. Results suggest that
population policy be accompanied by improvements in education and gender
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empowerment.

Other dominating tendencies and concepts in population-environment studies include

the incorporation of consumption patterns, population aging at different spatial scales
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and particularly in developed countries, and the reciprocity and multidisciplinarity of

the P-E relationship.

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Bibliography

Alexandratos, Nikos (2005). Countries with Rapid Population Growth and Resource Constrains: Issues
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countries)
Bernstein, Stan (2002). Freshwater and Human Population in Karin M. Krchnak, (ed.) Human
Population and Freshwater Resources. U.S. Cases and International Perspectives. Bulletin Series. 107,
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Bongaarts, John (1992) Population Growth and Global Warming, Population and Development Review,
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Bongaarts, John (1996) Population pressure and the food supply system in the developing world,
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Carr, David L., Laurel Suter and Alisson Barbieri (2005) Population Dynamics and Tropical
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Cohen, Joel (1995). How Many People Can the Earth Support? New York: Norton. (This is a classical
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book in which the author discusses the concept of carrying capacity and assesses several attempts to
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De Sherbinin, Alex and Victoria Dompka (1997) Water and Population Dynamics: Case Studies and
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El-Hinnawi, Essam (1985) Environmental Refugees. Nairobi: United Nations Environment Programme.
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Foley, Jonathan A. et al (2005) “Global Consequences of Land Use” Science 309: 570-574. (This study
discusses the localized effect of land use change and highlights the global nature of its impact).
Gleick, Peter H. (2003) Water Use in Annual Review of Environment and Resources. 28:275-314.
Harrison, (The author discusses the concepts and data availability to address the water use dynamics. He
highlights the possibilities for improving water supply and demand).
Paul and Fred Pearce (2000). AAAS Atlas of population & environment. Berkeley: University of
California Press-American Association for the Advancement of Science. (This Atlas represents an
important reference for the study of the relationship between population and environment dynamics).
Geist, Helmut J. and Eric J. Lambin (2002). Proximate Causes and Underlying Driving Forces of Tropical
Deforestation (2002) Bioscience (52), 2,143-150. (A very comprehensive meta-analysis of tropical
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Development Priorities? Working Paper EB2004-0001. Institute of Behavioral Science. Research
Program on Environment and Behavior. Boulder: University of Colorado at Boulder. (This is a very

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DEMOGRAPHY – Vol. II - Population, Natural Resources and Environment - Alan Jowett, Haydea Izazola

interesting study on the interactions between gender biased household strategies and priorities of
development issues among the rural population in Ghana).
Lutz, Wolfgang, Warren C. Sanderson and Sergei Scherbov (2004) The End of World Population
Growth. New Challenges for Human Capital formation and Sustainable Development. London and
Sterling, VA: IIASA-Earthscan. (This book demonstrates that instead of an environmental collapse as
some researchers forecast some decades ago, population growth will smoothly stabilize in the present
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Panayotou, Theodore (2000) Population and Environment. CID Working Paper No. 54. Environment
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and global food availability)
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world population will reach about 9.2 billion inhabitants).
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Zaba, Basia and Ndalahwa Madulu (1998) “A Drop to Drink? Population and Water Resources:
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Dynamics: Case Studies and Policy Implications. IUCN-PRB-USAID-AAAS. (Informative work on

water supply households strategies in Tanzania).
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Biographical Sketches

Haydea Izazola, Professor with Tenure, Universidad Autónoma Metropolitana-Xochimilco. National

Researcher, Mexican Research System, Level II. Ph.D. in Social Sciences with mention in Population
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Studies and Masters in Demography from El Colegio de México, A.C. BA in Economics from UNAM
(Mexico National University). Leadership for Environment and Development. LEAD México-El Colegio
de México. IV Cohort-Fellow. Mexico City. Her research interests include the relationship between
quality of life and quality of the urban environment in Mexico City, and in particular, between migration
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and the deterioration of environment, with a special focus on family and gender issues. She has edited
four books on the relationship between population dynamics and environment in Mexico.

Alan Jowett is research assistant and undergraduate student in Economics at Centro de Investigación y
Docencia Económicas (CIDE) in Mexico City. He has also participated in literacy campaigns in
communities experiencing high environmental degradation and out-migration

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