Population Growth

WORLD POPULATION

OCN 102: Introduction to the Environment, Climate Change and Sustainability

Population Growth & Sustainability

  • Instructor: Dr. Michael Cooney

  • Location: POST 104B

Population Estimates and Projections

  • 2050: Estimated world population: 9.7 Billion

  • 2047: Estimated world population: 9.5 Billion

  • 2012: World population reached 7 Billion

  • 1999: World population reached 6 Billion

  • 1987: World population reached 5 Billion

  • 1974: World population reached 4 Billion

Regional Population Distribution (Estimates)

  • Northern America: 491 million

  • Europe: 630 million

  • Latin America and the Caribbean: 680 million

  • Africa: 4.3 billion

  • Asia: 4.7 billion

  • Oceania: 75 million

Note: Regions follow United Nations definitions and may differ from other Pew Research Center reports.
Source: United Nations, Department of Economic and Social Affairs, Population Division, "World Population Prospects 2019."
Pew Research Center

Population Growth & Climate Change

Overview

  • Demographic Trends Impact:

    • Influence the magnitude of climate disruption.

    • Affect society's ability to adapt to climate change.

  • Rights-Based Policy Interventions:

    • Have potential to decrease fertility rates to align with sustainable population pathways.

    • Contribute to emission reductions and minimize climate risks.

  • Policy Recommendations:

    • Advocating humane policies to slow population growth should be an integral part of a comprehensive climate response.

Graphical Abstract of Climate Effects

  • Increased Risks:

    • Food Security

    • Water Security

    • Human Health

  • Climate Change Consequences:

    • Increased greenhouse gas (GHG) emissions

    • Average temperature rise

    • Extreme weather events

    • Sea level rise

Key Questions Surrounding Population and Climate Change

  • Essential Debate:

    • Which is more pressing: population growth or emissions from a small industrialized fraction of society?

    • Ethical considerations: Should global society regulate GHG emissions through policies targeting population control or fossil fuel use?

    • Alternative perspective: Some argue that population growth is not the central problem regarding climate change.

Modeling Growth: Survivorship Curves

Overview of Survivorship Curves

  • Definition: Graph showing the number or proportion of individuals surviving to each age for a species or group.

  • Population Growth Factors: Birth rate, death rate, and life expectancy represented over time.

  • Types of Survivorship Curves:

    • Type I: High survival rate in early and middle life; rapid decline in later life.

    • Type II: Constant mortality rate regardless of age.

    • Type III: Greatest mortality early in life, lower rates for survivors.

  • Significance: Type III organisms are more vulnerable to climate variability, influencing conservation strategies.

Reference Study: John M. Halley, Kyle S. Van Houtan, Nate Mantua. "How survival curves affect populations’ vulnerability to climate change." PLOS ONE | https://doi.org/10.1371/journal.pone.0203124 September 6, 2018

Survivorship Curves and Human Response to Climate Change

  1. Environmental Contributions:

    • Factors affecting survival curves include climate change.

  2. Type Environment Descriptions:

    • Type I: Genetic and physiological determinations of fecundity; environmental impact minimal.

    • Type II: Fertility and mortality effects independent of age.

    • Type III: Environmental effects are age-dependent.

  3. Key Questions Raised:

    • Will climate change modify the human survivorship curve?

    • Will impacts differ between rich and poor countries, or affect global human migration?

Modeling Growth Rate

Exponential Growth with Constant Growth Rate

  • Definition: Unconstrained natural population growth increases exponentially over time.

  • Example: Starting with one cell dividing every 20 minutes, the end population after 5 hours is 32,768 cells.

    • Exponential Growth Formula: P = P_0 e^{rt}

    • Where:

      • P: Population at time t

      • P 0: Initial population size

      • e = 2.718$ (Euler's number)

      • r: Growth rate

      • t: Time

Exponential Growth with Nonlinear Growth Rate

  • Key Point:

    • If the birth rate exceeds death rate, $r$ is positive; if the opposite holds, $r$ is negative.

  • Formula:

    • r(t) = b(t) - d(t)

    • Where:

      • $b(t)$: Birth rate at time $t$

      • $d(t)$: Death rate at time $t$

  • Key Question:

    • Will climate change accelerate deaths?

Logistic Growth Rate Model

  • Description:

    • Population growth slows as it approaches the carrying capacity ($K$).

  • Carrying Capacity ($K$):

    • Maximum population that can be sustained indefinitely based on available resources.

    • Acts as a moderating force when resources are limiting.

  • Logistic Growth Formula:

    • dP/dt = rP igg(1 - rac{P}{K}igg)

    • Where:

      • K: Carrying capacity

      • P: Current population size

  • Key Concept: As P nears K, growth slows incrementally.

Growth Limiting Factors

Environmental Resistance

  • Definition: Factors influencing logistic growth and impacting carrying capacity (K).

  • Types of Factors:

    • Density-Dependent Factors:

      • Regulate population based on density, inducing competition among individuals for resources.

      • Can control population size.

    • Density-Independent Factors:

      • Affect populations without regard to density; examples include pollution and natural disasters.

      • Climate change as a density-independent factor intensifying extreme weather.

Source: IPCC Working Group 2. 2014. "Climate Change 2014: Impacts, Adaptation, and Vulnerability."

Historical Population Growth

  • Historical Variability in Human Growth Rate: Demonstrated variability with drop during pandemics (e.g. Black Plague).

  • Impact of Black Plague:

    • Affected population densities during rapid urbanization; led to the death of two-thirds of Europe's population in three years.

Modeling Historical Population Growth

Exponential Growth Model

  1. Historical data suggests a averaged growth rate of 0.104% (from 7000 BC).

  2. Initial population estimate around 500,000 (7000 BC) yields impractical predictions with exponential models, indicating hyper-exponential growth is necessary for accurate modeling.

Logistic Growth Model

  1. Observation: Human population growth does not resemble natural species interactions with limiting factors.

  2. S-Shape Curve: Logistic growth can illustrate slow growth onset years before hitting population limits.

Consequences of Exceeding the Earth’s Carrying Capacity

  • Critical Question Addressed:

    • Should we control population growth, resource consumption, or emissions?

    • Alternatively, should we allow natural consequences to play out?

  • Impact of Ecosystems on Life:

    • The overall health of ecosystems directly influences all life and our Ellen on Earth's biosphere capacity.

  • Result of Exceeding Carrying Capacity: Abrupt population declines observed historically after surpassing ecological limits.