Population, migration, and environment

Ellen WiegandtIUHEI

Global average temperatures 1860-2002

Difference from 1961-1990 normals, °C

Adaptation to impacts

New migratory flows from South to North 

Developed world likely to fare better in relative terms than the developing world

But it cannot insulate itself from the impact of changes already poor regions

Population and environment

Fundamental problem of global environmental change:

Balance supply of resources from physical system with demand for these resources from human populations over time

Population and environment nexus

Does population growth have positive or negative effect on well being?

At what spatial scale? Over what time period?

Problems population-resource dynamics

A population “tragedy of the commons”

Problem of incorporating the future

Different periods; different views Mercantilist period: population growth

seen as positive to fuel commercial development

Malthus: fear that population could outstrip resources

19th and 20th centuries: significant economic growth Growth would spread: modernization

1960s: concern because of unprecedented population growth: the population explosion

World population growth

World gross domestic product (GDP)

Positive view: population-knowledge interactions Assumes exogenous population growth Leads to increase in output because of necessity

to intensify to keep pace with population. As real per capita incomes increase, have

specialization, including in specialization of knowledge

Larger population leads to larger increases in knowledge

More people, more likelihood of making significant discovery

New technologies provide larger relative benefits from productivity gains the larger the population

Two opposing views of future Global level statistics and long-term trends suggest

conditions will ultimately equalize. Underlying assumptions: Natural resource base imposes few constraints on growth;

knowledge can overcome them Increased labor productivity will allow both higher

populations and greater per capita income/wealth

Regional perspective suggests that specific conditions of population-environment interactions can lead to some persistent economic misery and environmental degradation Feedback loops between demographic behavior, institutions

and resource base lead to locally confined vicious circles; these widespread in vast numbers in poorest regions of the world

If this is the case, development will not necessarily trickle down

Or, at least will have periods of deep poverty and severe environmental problems

Population numbers and dynamics Static: count people

Taxpayers Laborers Potential soldiers: raise armies

Dynamic: planning Resource issues: food supply; sufficient

agricultural land Land management: urban/rural balance Future school population Social security, health policy (ex. Aging) Immigration policy

Sources of population information: Demography

Vital events: births, deaths, marriages

Used to calculate demographic characteristics and ratesLife expectancy Infant mortalityAge at marriageAge specific fertility rates

Age-specific fertility

Population-society-environment

What purely demographic factors determine population composition from period to period? Demographic models quite robust because of

the relative stability of rates: long lag effects What other societal and environmental

factors could influence demographic behavior? But can imagine changes in behavior that

would change rates

Malthusian theories of population Assumptions

Constant "passion between the sexes"Finite earth

Argument:Left unchecked, population grows and,

by definition, grows exponentially (passion)

After an initial period of strong growth, output as a function of population (labor) exhibits diminishing returns

Pre-industrial Western European Demographic Regime High mortality: “positive check” High Fertility Fertility Controls: “preventive checks”

Age at marriage Celibacy Spacing behavior Contraception Migration

Alternatives to Malthus: Boserup/Simon Relate technological progress to

population growth Population concentration leads to higher

likelihood of technological advance. Population growth longer hours, More labor-intensive techniques eventually

leads to more sophisticated technology

Synthesis argument: Lee, Ronald, Malthus and Boserup: A Dynamic Synthesis, In David Coleman and Roger Schofield, The State of Population Theory, Oxford: Basil Blackwell, 1986.

Limits to Malthusian Approach

Explaining emergence of new demographic regimes

How technology might explain shifts

These considerations important, because new regimes have emerged

Demographic transition

Characterized by a drop in marital fertility achieved through "stopping" behavior, i.e. controlling births after having the desired number of children

Demographic transition: the evidence

Shift from high to low fertility was a result of deliberate family limitation

Transition occurred rapidly once it began

To date, process has been mostly irreversible

Demographic transition

Proposed causes of transition Improvements in food supply

People could marry earlier Improvements in public health reduced mortality

Not just mortality decline but also infant and child mortality decline

Increasing urbanization Laws promoting education and setting labor standards Costs of children went up as did opportunity costs of having

them Increasing female literacy and employment also raise

opportunity costs of children Improvements in contraceptive technology help in the

second half of the 20th.C. Contraceptives were not widely available in the 19th.C.

Once decline started it continued and has now reached replacement or below replacement level in most western countries

Variation in conditions at transition Timing and extent of decline in mortality Infant mortality varied Levels of marital fertility differed Extent of urbanization differed at

transition France 1800: 70% male labor force in

agriculture England 1892: 15% male labor force in

agriculture Levels of literacy varied

Baby boom United States

Fertility Declines, Real and Projected

1

2

3

4

5

6

7

1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050

Chi

ldre

n pe

r Wom

an (2

.1 =

no

popu

latio

n gr

owth

)

Developing

Developed

Africa

Asia

South and CentralAmerica

Stabilization Remains a Challenge

0

1

2

3

4

1950 2000 2050

Stab

iliza

tion

Ratio

(birt

hs/d

eath

s) (1

= n

o po

pula

tion

grow

th)

Developing Developed Africa Asia South and Central America

Sub-Saharan African Fertility Regime

Low age at marriage Polygyny: men have many wives,

leaving few women celibate Acceptance of pre-marital and extra-

marital sexual relations Remarriage after widowhood or divorce

is the norm

These are all factors that make women susceptible to childbearing throughout their reproductive period of 15-49.

Differences Pre-industrial European and African Regimes

Europe: reduce "exposure"

Africa: spacing behavior

Fertility Declines, Real and Projected

1

2

3

4

5

6

7

1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050

Chi

ldre

n pe

r Wom

an (2

.1 =

no

popu

latio

n gr

owth

)

Developing

Developed

Africa

Asia

South and CentralAmerica

Characteristics of Sub-Saharan African Social System Poorly defined or poorly enforced common

property systems Children reared communally (polygyny)

Share “costs” in time or responsibility Weak conjugal bonds Lineage holds land

Large families have access to larger share

References: Dasgupta; Partha, The Population Problem: Theory and Evidence Journal of Economic Literature, 33, 4, 1995: 1879-1902; Chichilnisky, Graciela, North-South Trade and the Global Environment, The American Economic Review 84 (4): 851-874.

Changes in life expectancy in selected African countries with high and low HIV prevalence: 1950 - 2005

with high HIV prevalence:

Zimbabwe

South Africa

Botswana

with low HIV prevalence:

Madagascar

Senegal

Mali

Source: UN Department of Economic and Social Affairs (2001) World Population Prospects, the 2000 Revision.

30

35

40

45

50

55

60

65

Lif

e e

xp

ecta

ncy

(y

ears

)

1950– 1955

1955- 1960

1960-1965

1965-1970

1970-1975

1975-1980

1980-1985

1985-1990

1990-1995

1995-2000

2000-2005

Migration: Definition

A permanent change in residenceSpatial aspect

Distinguish internal, international Internal: within a country International: cross borders

Legal Illegal Refugees

Measurement issues

What is meant by permanent? How far do you have to move to be

considered migrant? Despite ambiguities, have indices;

calculate rates similar to fertility, mortality rates Crude or gross out-migration/in-migration

rate: flow of people who leave/enter region over given time period

Net rate: difference between two Can be zero and still have lots of population

movements

Causes of migration Push: escape from economic, social, political

considerations that come to be seen as unacceptable

Pull: drawn to perceived better conditions To some degree, these two forms overlap with

what is described as voluntary and involuntary migration Involuntary: push Voluntary: pull

However, even in case of involuntary the decision to actually leave may be conscious choice and may take place when have perception that there opportunities elsewhere (pull)

Migration as a process

Underlying conditions for migration in general Environmental, economic, social condition Household factors Individual propensity for risk Community networks

Reasons for timing and place of migration Cost/benefit characteristics

Produce actual decision to migrate

Theories of migration

One of main explanations for migrations is economic: migration due to wage differential

Puzzle: why continuing migration to big developing country cities with overcrowding and high unemployment

Harris and Todaro model

Explain puzzle of migration using a two sector model with a rural (agricultural) and an industrial economy

Wages in agriculture are determined by agricultural production and prices

Wages in industry, generally located in urban areas, are dependent upon a minimum wage

Equilibrium conditions

As long as the urban, industrial wages are higher than agricultural wages, migration from rural areas to urban areas will occur

This even when there is unemployment in citiesNot wage itself but expectation of

wage

Other causal factors

Existing social networks that support newcomers

Increasing returns to scale in cities High paying jobs

Even if difficult to obtain, raises average wage

Segmented labor marketAlso raises average wage

Foreign aid and relief can accelerate the process

Pre-conditions as push factors

Climate change Reduce net profits made from agricultural

production Floods, sea level rise, etc. reduce available

land, other resources Resource-related factors that increase

the capacity to sustain local populations become dis-incentives to migration Role of property rights emerge again as

important determinant Clear and well-enforced rules important to provide

incentives for sustainable use Expansion and consolidation of common property

as way to provide flexible access to resources

Who migrates?

Age criteria Young adults: working age populations Link to development: rural to urban migration

provides labor for industrialization Link to life cycle: young leave parental

household and establish independent one based on employment

Gender criteria Often males But female migration is increasing

Impacts of migration on local environments Perceived short-term nature of stay may lead to

unsustainable resource use Property rights unclear: no mechanisms to insure

long-term efficient use Often confined to restricted areas: forced to

overuse resources to meet immediate needs May not know details of local conditions:

inefficient use resources Borders are arbitrary: may have population

distributions that not related to environmental conditions

Consequences Deforestation Land degradation Overuse water resources

Issues for the future Evolution of African population patterns

Is transition under way? Will AIDs-type situations reduce any beginning fertility

decline How will regions where population is below

replacement rate respond? Stay with lower population levels or have new baby

boom type response Pro-natalist policies especially in response to social

security-type issues Role of migration in redistributing population

Attitudes of host countries Role of climate change as aggravating factor

International migration policy

International agreements on population movements focus on political aspects, reflect post-WWII concerns

Inadequate to deal with other forces Economic Environmental

Definition of new human rights puts pressure on migration policy European Union tightens immigration rules Contradiction between extension of concept

of human rights and mechanism to deal with guaranteeing those rights