Human influences on the environment

What you'll learn

This topic examines how human activities affect ecosystems and the natural environment. You'll explore the consequences of population growth, pollution, habitat destruction and resource exploitation, alongside strategies for conservation and sustainable development. Understanding these concepts is essential for Paper 2 and extended-response questions that assess your ability to analyse environmental issues and evaluate solutions.

Key terms and definitions

Deforestation — the permanent removal of forest or woodland to use the land for other purposes, such as agriculture or urbanisation.

Eutrophication — the excessive enrichment of water bodies with nutrients (particularly nitrates and phosphates), leading to algal blooms and oxygen depletion.

Bioaccumulation — the build-up of toxic substances in the tissues of organisms over time, becoming more concentrated at each trophic level of a food chain.

Sustainable development — meeting the needs of the present population without compromising the ability of future generations to meet their own needs.

Biodiversity — the variety of different species living in a habitat or ecosystem, including genetic diversity within species.

Conservation — the protection and management of natural resources and ecosystems to prevent destruction and maintain biodiversity.

Fertiliser — a substance containing minerals (particularly nitrogen, phosphorus and potassium) added to soil to increase crop yield.

Greenhouse gases — gases in the atmosphere that trap heat, including carbon dioxide, methane and water vapour, contributing to global warming.

Core concepts

Population growth and food production

Human population has grown exponentially from approximately 1 billion in 1800 to over 8 billion today. This growth creates increased demand for:

• Food production
• Fresh water
• Energy resources
• Living space
• Raw materials

To meet food demands, agricultural practices have intensified through:

Monoculture farming involves growing single crop species over large areas. This maximises yield per hectare but reduces biodiversity, increases pest vulnerability and depletes specific soil nutrients. The soil becomes exhausted and requires heavy fertiliser application.

Intensive livestock farming concentrates animals in confined spaces with controlled feeding regimes. This produces maximum meat, milk or eggs per unit area but generates large quantities of waste, requires high antibiotic use and raises animal welfare concerns.

Use of fertilisers replaces minerals removed from soil by harvested crops. Nitrogen, phosphorus and potassium promote rapid plant growth, increasing yields significantly. However, excessive application leads to environmental problems through leaching into water systems.

Pesticide application kills organisms that damage crops, reducing losses. Chemical pesticides include:

• Insecticides (killing insects)
• Herbicides (killing weeds)
• Fungicides (killing fungal pathogens)

Problems arise because pesticides may kill non-target species, accumulate in food chains and allow pests to develop resistance through natural selection.

Pollution and its effects

Air pollution occurs when harmful substances contaminate the atmosphere:

Carbon dioxide (CO₂) concentration has increased from 280 ppm pre-industrially to over 420 ppm today due to:

• Combustion of fossil fuels (coal, oil, natural gas)
• Deforestation reducing photosynthetic CO₂ removal
• Increased respiration from larger populations

Excess atmospheric CO₂ is a greenhouse gas that absorbs and re-radiates infrared radiation, causing the enhanced greenhouse effect. This leads to global warming with consequences including:

• Rising sea levels from thermal expansion and ice cap melting
• Changes in precipitation patterns causing droughts and floods
• Shifts in species distribution as habitats become unsuitable
• Increased frequency of extreme weather events

Methane (CH₄) is released from:

• Digestive processes in cattle and rice paddies
• Decomposition in landfill sites
• Extraction and transport of fossil fuels

Methane is a more potent greenhouse gas than CO₂ but present in lower concentrations.

Sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are produced by burning fossil fuels, particularly in power stations and vehicle engines. These gases dissolve in atmospheric water vapour forming sulfuric and nitric acids, which fall as acid rain. Consequences include:

• Damage to leaves and reduced photosynthesis in plants
• Acidification of lakes and rivers, killing aquatic organisms
• Mobilisation of toxic aluminium ions in soil
• Corrosion of limestone buildings and metal structures

Water pollution contaminates aquatic ecosystems:

Eutrophication occurs when excess fertilisers leach from agricultural land into water bodies. The process follows this sequence:

1. Nitrates and phosphates enter rivers or lakes
2. Algae grow rapidly forming a dense bloom on the surface
3. Light penetration to submerged plants is blocked
4. Plants die as photosynthesis cannot occur
5. Aerobic bacteria decompose dead organic matter, consuming oxygen
6. Dissolved oxygen levels fall dramatically (hypoxia)
7. Fish and other aerobic organisms suffocate and die
8. Only anaerobic bacteria survive, producing foul-smelling compounds

Sewage contains organic matter and pathogens. Untreated discharge leads to:

• Bacterial decomposition depleting oxygen (similar to eutrophication)
• Spread of waterborne diseases (cholera, typhoid)
• Toxicity to aquatic life

Plastic pollution particularly affects marine environments. Plastics persist for hundreds of years, breaking into microplastics that:

• Are ingested by organisms causing internal damage
• Enter food chains and bioaccumulate
• Release toxic chemicals as they degrade

Insecticide bioaccumulation demonstrates the dangers of persistent chemicals:

DDT and other organochlorine pesticides accumulate in fatty tissues. As small organisms absorb pesticides, their predators consume many contaminated prey items, concentrating the toxin at each trophic level. Top predators like birds of prey accumulate lethal concentrations causing:

• Reproductive failure (thinning of eggshells)
• Nervous system damage
• Death

This process exemplifies biological magnification up food chains.

Deforestation

Forests are cleared for:

• Timber extraction for construction and fuel
• Agricultural land (crops and cattle grazing)
• Urban development and infrastructure
• Mining operations

Consequences of deforestation:

Climate impacts:

• Increased atmospheric CO₂ as trees are burned or decompose
• Reduced CO₂ absorption as photosynthesis decreases
• Contribution to global warming
• Altered rainfall patterns as transpiration decreases

Soil degradation:

• Erosion as tree roots no longer bind soil
• Leaching of nutrients during heavy rainfall
• Loss of humus when leaf litter no longer decomposes
• Desertification in vulnerable areas

Biodiversity loss:

• Habitat destruction forcing species extinction
• Disruption of food chains and webs
• Loss of genetic resources including potential medicines
• Reduced ecosystem resilience

Tropical rainforests like the Amazon contain over 50% of terrestrial species despite covering only 6% of land area, making their preservation critical for global biodiversity.

Conservation and sustainable resource management

Conservation strategies aim to protect species and habitats:

Protected areas including national parks and nature reserves restrict damaging activities. Examples include:

• Kruger National Park (South Africa) protecting African megafauna
• Galapagos Marine Reserve (Ecuador) preserving unique endemic species
• UK Sites of Special Scientific Interest (SSSIs) protecting habitats

Captive breeding programmes maintain populations of endangered species in zoos and wildlife parks, allowing later reintroduction. Success stories include:

• Arabian oryx recovered from extinction in the wild
• California condor populations increased through intensive breeding

Sustainable forestry involves:

• Selective logging removing only mature trees
• Replanting programmes ensuring regeneration
• Rotation systems allowing forest recovery between harvests
• Maintaining biodiversity corridors

Fishing quotas and regulations prevent overfishing by:

• Limiting catch sizes and species
• Enforcing minimum mesh sizes allowing juvenile fish to escape
• Establishing no-fishing zones for breeding
• Banning harmful practices like bottom trawling

Sustainable agriculture reduces environmental impact through:

• Crop rotation preventing nutrient depletion and pest build-up
• Organic farming avoiding synthetic pesticides and fertilisers
• Integrated pest management combining biological and chemical control
• Reducing livestock density to decrease waste pollution

Renewable energy sources replace fossil fuels, reducing CO₂ emissions:

• Solar panels converting sunlight to electricity
• Wind turbines harnessing kinetic energy
• Hydroelectric dams using gravitational potential energy
• Biofuels from crops (though these reduce food-growing land)

Waste management strategies include:

• Recycling materials (paper, metal, glass, plastic) to reduce resource extraction
• Composting organic waste producing nutrient-rich soil additive
• Reducing single-use plastics through legislation and behaviour change
• Treating sewage in biological treatment plants before discharge

The need for conservation

Reasons to conserve species and habitats:

Ethical arguments:

• All species have a right to exist regardless of human benefit
• Humans have moral responsibility to protect environments we've damaged
• Future generations deserve to experience natural diversity

Economic reasons:

• Ecotourism generates revenue (e.g., gorilla tracking in Rwanda)
• Wild species provide genetic resources for crop improvement
• Natural products yield medicines (e.g., rosy periwinkle treating leukaemia)
• Ecosystem services like pollination and water purification have monetary value

Ecological reasons:

• Biodiversity maintains ecosystem stability and resilience
• Food web complexity prevents population crashes
• Genetic diversity within species allows adaptation to environmental change
• Keystone species like predators regulate entire ecosystems

Worked examples

Example 1: Explain how eutrophication causes fish death in rivers receiving fertiliser runoff. [4 marks]

Model answer:

• Excess nitrates/phosphates from fertilisers enter the water [1]
• Algae grow rapidly forming a surface bloom that blocks light [1]
• Plants beneath die as photosynthesis cannot occur without light [1]
• Aerobic bacteria decompose dead organic matter, using up dissolved oxygen, so fish suffocate [1]

Examiner tip: This sequence must be in logical order. The mark scheme requires understanding the causal chain, not just listing effects.

Example 2: Describe and explain two ways that deforestation contributes to climate change. [4 marks]

Model answer:

• Trees are burned or decompose, releasing carbon dioxide into the atmosphere [1], which is a greenhouse gas that contributes to global warming [1]
• Removal of trees reduces photosynthesis [1], so less carbon dioxide is removed from the atmosphere [1]

Examiner tip: The question asks you to both describe (what happens) and explain (why it matters). Each way needs both components for full marks.

Example 3: Evaluate the use of intensive farming methods to increase food production. [6 marks]

Model answer:

Advantages:

• Produces more food per unit area of land, feeding growing populations [1]
• Increases efficiency of resource use, making food cheaper [1]
• Controlled conditions reduce crop/livestock losses from disease [1]

Disadvantages:

• Heavy fertiliser use leads to eutrophication when runoff enters waterways [1]
• Pesticides bioaccumulate in food chains, harming wildlife [1]
• Reduces biodiversity through monoculture and habitat loss [1]

Examiner tip: "Evaluate" requires balanced consideration of both sides. Structure your answer clearly with advantages and disadvantages. Higher-level responses might conclude with a judgment.

Common mistakes and how to avoid them

• Confusing greenhouse effect with ozone depletion — these are completely separate issues. The enhanced greenhouse effect causes global warming through CO₂ and methane trapping heat. Ozone depletion (caused by CFCs) increases UV radiation reaching Earth but is not part of the IGCSE specification.

• Describing eutrophication incompletely — many students mention algae and oxygen but omit critical steps. Always explain: fertiliser enters water → algae bloom → light blocked → plants die → bacteria decompose → oxygen depleted → fish die. The complete sequence is essential.

• Stating pesticides "poison" organisms without specificity — use precise terms like bioaccumulation and biological magnification. Explain that persistent pesticides concentrate at each trophic level, reaching toxic levels in top predators.

• Mixing up conservation methods — distinguish between in-situ (protecting habitats in their natural location) and ex-situ (captive breeding in zoos). Know specific examples for each approach.

• Vague descriptions of deforestation effects — link each consequence to a mechanism. Don't just say "less oxygen" (actually, photosynthesis and respiration balance globally). Focus on increased CO₂, soil erosion and biodiversity loss with clear explanations.

• Writing "global warming causes pollution" — the causation is reversed. Pollution (particularly greenhouse gas emissions) causes global warming. Precision in cause-and-effect relationships is crucial for higher marks.

Exam technique for "Human influences on the environment"

• "Describe" questions require factual statements about what happens without explanation. For example, "describe how deforestation occurs" needs methods (burning, logging) and purposes (agriculture, development) but not consequences.

• "Explain" questions demand reasoning and mechanisms. Use linking words like "because," "therefore," "so that" and "this causes" to show causal relationships. For 3-mark explanations, provide a logical sequence with three distinct points.

• Extended response questions (5-6 marks) need structured answers. For "suggest" or "evaluate" questions, consider multiple perspectives or several solutions. Use paragraph structure and conclude evaluation questions with a judgment if appropriate.

• Data interpretation questions about environmental topics require you to describe trends precisely using values from graphs or tables, then explain patterns using biological knowledge. Always quote data when describing and link to processes when explaining.

Quick revision summary

Human activities cause extensive environmental damage through population growth demands. Agricultural intensification increases food production but creates pollution through fertiliser eutrophication and pesticide bioaccumulation. Fossil fuel combustion releases greenhouse gases causing global warming, while acid rain damages ecosystems. Deforestation increases atmospheric CO₂, causes soil erosion and destroys biodiversity. Conservation strategies including protected areas, sustainable practices and renewable energy aim to balance human needs with environmental protection. Understanding causal sequences and specific mechanisms is essential for exam success on this topic.