Environmental Systems and Societies | Human populations and urban systems

Hello ESS Students! Welcome to Human Populations and Urban Systems (Topic 8)

This topic is absolutely crucial for understanding ESS because it connects the "S" (Societies) back to the "E" (Environmental Systems). We are going to explore how our numbers (population size) and our locations (cities) affect the planet's ability to cope.

Don't worry if demographic graphs look intimidating at first. We will break them down step-by-step. By the end of this chapter, you will be able to analyze why some countries are growing quickly and why others are shrinking!

8.1 Understanding Human Population Dynamics

The Basics of Population Change

Population size is a dynamic process—it's always changing! The overall change in population is determined by four key factors:

Population Change = (Births + Immigration) - (Deaths + Emigration)

In ESS, we often look at rates (per 1,000 people per year) rather than total numbers:

• Crude Birth Rate (CBR): Number of live births per 1,000 people in a population per year.
• Crude Death Rate (CDR): Number of deaths per 1,000 people in a population per year.
• Natural Increase Rate (NIR): The percentage growth per year.

Quick Formula Review:
The Natural Increase Rate (NIR) is calculated as:
$$ \text{NIR} = \frac{(\text{CBR} - \text{CDR})}{10} $$ (We divide by 10 because the rates are "per thousand" and we want the final answer as a percentage.)

Population Growth Curves: J-Curves and S-Curves

How fast do human populations grow? We can model this using two types of curves:

1. The J-Curve (Exponential Growth)

• This occurs when a population increases at an accelerating rate (like compounding interest).
• Growth is currently unrestricted by external factors (plenty of resources, no predators/diseases).
• Example: The global human population for most of the 20th century followed a J-curve due to medical advances and increased food production.

2. The S-Curve (Logistic Growth)

• Growth starts exponentially but then slows down as the population nears the environment's carrying capacity (K).
• This slowdown is caused by environmental resistance (e.g., lack of food, build-up of waste, disease).
• Most natural populations exhibit S-curve growth, stabilizing around K.

Age/Sex Pyramids: Reading the Structure

Age/sex pyramids (or population pyramids) are bar charts that show the distribution of a population by age and gender. They are incredibly useful for predicting future population changes.

Remember this simple structure:

• Base: Represents younger people (pre-reproductive age). A wide base means high birth rates and rapid future growth potential (like a traditional triangle).
• Middle: Represents working adults (reproductive age).
• Top: Represents older people (post-reproductive age). A narrow top means low life expectancy.

Three Main Pyramid Shapes:

1. Expanding (Rapid Growth):
Shape: Wide base, narrow top (a true triangle).
Characteristics: High birth rates, low life expectancy, typical of low-income or developing nations. Example: Niger or Afghanistan.

2. Stable (Slow or Zero Growth):
Shape: More rectangular or column-like.
Characteristics: Birth rate and death rate are roughly equal. This indicates a stable population where the replacement fertility rate is being met. Example: USA or France.

3. Contracting (Declining Growth):
Shape: Narrow base, wider middle and top (looks like an inverted triangle or beehive).
Characteristics: Birth rates are falling below replacement level; the average age is high. Example: Japan or Germany.

8.2 The Demographic Transition Model (DTM)

The Demographic Transition Model (DTM) explains how birth rates (CBR) and death rates (CDR) change over time as a country develops economically and socially. It is a powerful concept in ESS.

The Five Stages of the DTM

The DTM tracks population growth through five predictable stages:

Stage 1: High Stationary

• CBR: Very High (Need for children as farm labor; lack of contraception).
• CDR: Very High (Disease, famine, poor hygiene, little medicine).
• Population Growth: Very Low/Zero.
• Context: Pre-industrial societies (no country is purely in Stage 1 today).

Stage 2: Early Expanding

• CBR: High (Social norms remain the same).
• CDR: Rapidly Falling (Improved sanitation, hygiene, and medical care).
• Population Growth: Very High. This is the stage of maximum population increase.
• Context: Developing countries experiencing industrialization, like Nigeria.

Stage 3: Late Expanding

• CBR: Falling (Increased urbanization, education for women, accessibility of contraception, children are now an economic cost).
• CDR: Still Falling, but slowly (Reaching minimum levels).
• Population Growth: Slowing down significantly.
• Context: Rapidly industrializing countries, like India or Brazil.

Stage 4: Low Stationary

• CBR: Low.
• CDR: Low (High life expectancy).
• Population Growth: Very Low/Zero.
• Context: Developed economies, high standards of living, such as the UK or Australia.

Stage 5: Declining (The New Stage)

• CBR: Below CDR (Fertility rate falls below replacement level of 2.1).
• CDR: Low (but may slowly increase due to aging population).
• Population Growth: Negative (population size shrinks).
• Context: Countries facing population aging and labor shortages, like Japan or Italy.

Factors Influencing Fertility Rates

The number of children born per woman (Total Fertility Rate, TFR) is influenced by complex societal factors:

• Access to Healthcare and Contraception: Easy access allows people to choose family size.
• Urbanization: Children are expensive liabilities in cities, not economic assets as in rural farming areas.
• Cultural/Religious Values: Some cultures encourage large families.
• Government Policy: Policies can encourage growth (e.g., tax breaks for children) or restrict it (e.g., China's historic one-child policy).

8.3 Population, Carrying Capacity, and Ecological Footprints

Redefining Carrying Capacity (K) for Humans

In Topic 2, we defined Carrying Capacity (K) as the maximum number of a species that an environment can sustainably support.

For humans, determining K is extremely complex because:

1. Technological Innovation: We can temporarily overcome resource limits (e.g., by developing new fertilizers or desalinating water).
2. Resource Substitution: We can swap out dwindling resources for others (e.g., oil for solar power).
3. Importing Resources: A country can exceed its local K by importing food, water, and energy from elsewhere.
4. Quality of Life: Do we calculate K based on a subsistence lifestyle (minimum resources) or a high standard of living (maximum resources)? ESS often focuses on the latter.

Therefore, a more useful measure for human impact is the Ecological Footprint (EF).

The Ecological Footprint (EF)

The Ecological Footprint is the area of land and water required to provide all the resources a person/population consumes and to absorb the waste they produce.

• It is measured in global hectares (gha).
• It allows us to compare resource demand against nature's ability to regenerate resources (Biocapacity).

The key connection: If a population's EF is greater than the available biocapacity of the area it lives in, the region is in an ecological deficit (or overshoot). It is unsustainable and relies on importing resources or degrading its own natural capital.

Factors Affecting the Size of an EF:

The footprint is usually much larger in high-income countries (HICs) than in low-income countries (LICs), driven by:

• Level of Consumption: High meat intake, frequent travel, large homes, and purchasing many goods.
• Technology Used: Reliance on fossil fuels vs. renewable energy (carbon footprint is the biggest component).
• Waste Management: How much waste is produced and whether it is effectively recycled or processed.

8.4 Urban Systems and Sustainable Management

The Growth of Cities (Urbanization)

Urbanization is the process where an increasing proportion of the population lives in cities and towns. Today, more than half of the world's population lives in urban areas.

Cities are complex systems that require massive inputs and generate significant outputs.

Cities as Open Systems:

• Inputs: Food, water, energy (fossil fuels, electricity), raw materials (wood, metal), people.
• Outputs: Solid waste, sewage, air and water pollutants, heat, manufactured goods, waste heat, noise.

The concentration of these inputs and outputs leads to significant local and global environmental impacts:

• Local Impact (Waste & Pollution): Creation of landfill sites, high air pollution (smog), and localized high temperatures (Urban Heat Island effect).
• Regional Impact (Resource Demand): High demand for water often stresses water sources far outside the city (e.g., rivers diverted for city use).
• Global Impact (Carbon Footprint): Cities are huge energy consumers, contributing significantly to global carbon emissions and climate change.

Strategies for Sustainable Urban Management

The goal of Sustainable Urban Management is to maximize the efficiency of urban systems while minimizing their environmental footprint. This is essential for meeting the needs of present and future generations.

1. Improving Transportation Systems

• Promoting Public Transport (buses, trains, trams) to reduce private car use.
• Creating pedestrian and cycling infrastructure.
• Introducing congestion charges or low-emission zones (LEZs).

2. Energy and Resource Efficiency

• Mandating energy-efficient buildings and appliances.
• Using Renewable Energy Sources (solar panels on buildings, urban wind farms).
• Implementing smart grids to manage electricity distribution efficiently.

3. Waste and Water Management

• Promoting the Circular Economy (designing out waste, maximizing reuse and recycling).
• Implementing effective sewage treatment and waste-to-energy schemes.
• Using Rainwater Harvesting and greywater recycling systems to reduce demand on external water sources.

4. Green Infrastructure

• Increasing urban green spaces (parks, green roofs, vertical gardens). This helps mitigate the Urban Heat Island effect, absorbs CO2, and improves biodiversity.
• Using permeable paving to reduce surface run-off and prevent urban flooding.