8.4 Human Population Carrying Capacity

Carrying Capacity (k) Defined 

Maximum number of individuals of a species that an ecosystem can support 

• Often human-determined 

• Easy to determine for wild animals; for humans it’s not so easy 

• Resources all life requires: water, food/ energy, shelter/ space 

  • What different things do humans need to survive?  (reasons human k is hard to calculate)

    • Transportation, medicine/ health care, minerals, clothing, electricity/ appliances/ technology … humans use a lot of stuff that impacts the Earth

    • Human needs vary by region (think MEDC vs LEDC)

    • Whose standard of living is correct? 

Ecological Footprint (EF)

• A model used to determine if humans are living within our carrying capacity

• Assesses human impact & sustainability 

Is a population living sustainably within an area?

• Consider food, space, water to support a population without causing damage 

  • Bison in Yellowstone NP: 2500 to 4500 depending on available food 

    • When population gets too large, individuals are culled from the herd (killed)

  • Deer in Valley Forge NP: k= 31-35 deer/ mi² (in 2009 there were 241 deer/ mi²)

• Mean (average) population size is typically within carrying capacity

  • If population < k then either J or S curve (see 2.1.3 notes)

    • Recall r & k strategists 

Determining human carrying capacity (k)

• Waste isn’t all biodegradable leads to environmental degradation

• Resources vary

  • Luxuries & necessities   

• Human population moves goods via Global Trade

  • Food imports/ exports

  • imports/ exports other goods

• Technology - makes life easier, but can be bad for the environment (could be good too)

  • BAD: pollution from mining of resources to production to shipping of products to disposal 

  • GOOD: solar panels, biofuels, energy efficient appliances & cars, design for circular use, explore options for helping survival (GE foods), using tech to predict weather & climate change 

• Because of the above points, it is hard to determine

Waste

produced at a rate greater than environment can assimilate it

Resources

• range is greater than what other species need

• farmers

  • subsistence: use less pesticides, fertilizers, space than commercial farmers (use machinery (needs FFs), pesticides, fertilizers, lots of water, use GMO seeds)

• predator-prey relationship

  • predators tend to use more space, have a lower carrying capacity than prey

    • bc need to eat more to combat entropy

Imports

• Global trade of foods

  • constant supply of produce that used to only be available seasonally + exotic foods from other places

• Waste is imported/ exported

  • Sweden imports trash to make energy 

  • U.S. used to export recycling to China

  • Chester, PA incinerator gets trash from other states  

Technology

• Includes tools (modern & primitive), early agricultural, fossil fuels, fire

• Anything that can be used to do work & make it easier 

Local or global?

• All of the above vary by region and even within countries.

Earth’s carrying capacity

• UN, 2001: between 4-16 billion people

  • Median is 10 billion  

  • Estimates can drop due to resource depletion coupled with increased consumption 

• Models based on Malthus + his opponents 

• Can Earth continue to sustain us?

• Can we create technology to keep living sustainably?

2 aspects

• Biocapacity = Earth’s bioproductive land + sea 

  • Forests, croplands, pastures, fisheries

  • Land available to grow food & absorb waste 

  • Measured in Gha (global hectare) = 100 m² (inside of a 400 m track)

• Demand = the amount of bioproductive land needed for resources + space for infrastructure & waste disposal

• WWF, 2014: global EF in 2010 was 18.1 billion gha (2.6 gha person)

  • 1.7 gha is biocapacity available 

  • 0.9 gha is a shortfall (using more than we have)

Things used to measure EF

• Energy

  • Renewable or nonrenewable

• Travel/ transportation

  • Individual or public transportation

  • Fuel type + emissions

  • Air travel

• Goods (stuff)

  • Food, clothing, gadgets, other things we consume 

Infrastructure + settlements take up space

• Human needs take space away from (urbanization)

  • Forests & other ecosystems

  • Agricultural lands

• Less forests & natural ecosystems reduces the number of plants to absorb carbon dioxide: waste of combustion of FF + wood/forests

• More space used increases footprint

Food + fiber

• Comes from pastures & croplands

  • Inputs to growing the crops & animals (water, fertilizers or food, space, pesticides)

  • Are animals pasture raised or raised inside

• Non- food crops:

  • Sugar, corn, sorghum for biofuel (ethanol)

  • Cotton, flax, silk

  • Pharmaceuticals

  • Tobacco 

  • Coffee, tea

• Seafood: wild caught vs. farmed

• Food miles!

More specific footprints

• Carbon

  • Total carbon based GHGs emitted via industry, domestic, event, flight, locality, country

• Water

  • Amount of water used for washing & drinking, and used to grow food

  • Estimate: 800 L water is needed to make 1 L milk

• Food

  • How much food a human needs (where does the food come from?)

  • Based on the land needed to raise crops/ animals/ animal feed and the land needed to absorb carbon emissions from food production or fishing 

Case Study: Peru’s EF

Demographic data

• CBR: 18.28

• CDR: 6.01

• NRI: 1.28 (natural rate of increase)

• DT: 57 yrs

• Growth Rate: 12.26

• EF & biocapacity per person

  • Peru has a credit

Abundant natural resources

• Rainforests 

• Overuse of resources 

• Hazards 

• Fe, Cu, Au, Ag, petroleum. wood, fish, coal. gas, hydropower

GDP per capita: US $6500

Why a low EF? What might be changing?

• lots of resources but less of a need, however their biocapacity is falling → incr. pop + decr. in bioproductive land

16% of pop. has no access to H2O; 28% no access to sanitation

EF: 1.54 gha/person

biocapacity: 3.86 gha/person

+2.32 gha/person credit!

Earth Overshoot Day

The day each year when we have used all the resources for the year

• Global biocapacity x 365

         world EF

Agenda 21

1992 Earth Summit in Rio 

178 countries adopted the agenda

1. Social & economic dimensions to deal with poverty, consumption & health

2. Conservation & management resources for development 

3. Strengthen roles of women, children, NGOs, local municipalities & indigenous people 

4. Implementation: how to get it done using science, technology, education & international institutions   

The Planetary Boundaries Model

• Created by Johan Rockström & 28 other reputable scientists

• Identified 9 quantifiable “planetary boundaries” 

  • Each boundary involves regulatory processes that help Earth's resilience & stability

  • Crossing a boundary increases the risk of creating irreversible environmental changes since there are limits to development

• “Up to what limits will the Earth system be able to absorb human activities without compromising the living conditions of species?”

• Model was revised in 2022 since much more data was available

  • As more data becomes available, it can be further revised

Uses of the Planetary Boundaries Model

• Human disruptions to various systems on Earth is scientifically identified using data

• Includes many more systems than just climate change

• Can be an alert to action for both the public and policymakers

Limitations

• Only concerned with ecological systems (environmental justice cannot be considered since the human aspect is not included)

• Boundaries change as new data is obtained (“a work in progress”)

• It is a global model- may not apply to every locality/ country

The Doughnut Economics Model

• A framework to create a regenerative & distributive economy that meets the needs of ALL people 

• 2 concentric rings

  • Inner ring: social foundation

    • To ensure that everyone has access to life’s essentials

    • Based on social SDGs

  • Outer ring: ecological ceiling

    • ensures that we don’t surpass the planetary boundaries to protect Earth’s support systems 

    • Based on planetary boundary science 

  • Combined they represent the minimum needed for an ecologically & socially just economic system

Key Terms

Uses of the Doughnut Model

• Supports environmental justice 

• Is being used at different scales (national level through localites)

• Supports sustainable action 

• Has reached popular awareness 

Limitations of the Doughnut Model

• Still being worked on 

• If individuals are focused on their own wealth it won’t work

• Principles of regenerative & distributive practice are toop broad

• No specific policies