Current Environmental Crises
The Big Picture🌍 The Scale of Human Impact
Humans have altered more than 75% of Earth's land surface, triggered a sixth mass extinction, changed the chemistry of the atmosphere and oceans, and disrupted every major biogeochemical cycle. These changes are happening faster than at any point in the last 65 million years. The current era is increasingly called the Anthropocene — the epoch of human-dominated Earth.
The crises are interconnected: deforestation drives climate change which accelerates biodiversity loss which reduces ecosystem services which affects human food and water security. Understanding the links between these problems is as important as understanding each one individually.
Climate Change
Burning fossil fuels adds CO₂ to the atmosphere, trapping heat. Global average temperature has risen ~1.2°C since 1850.
Biodiversity Loss
Species are going extinct 100–1000× faster than the natural background rate. The sixth mass extinction is underway.
Pollution
Air, water, and soil pollution from industry, agriculture, and waste affects all ecosystems and human health.
Water Crisis
Overextraction, pollution, and climate change are depleting freshwater supplies for 2 billion people.
Deforestation
~10 million hectares of forest lost per year — releasing carbon, destroying habitat, and disrupting water cycles.
Food Security
Soil degradation, water scarcity, and climate shifts threaten agricultural productivity for a growing population.
⚠️ Exam Watch — Direct vs Indirect Human Impact
Examiners often ask you to distinguish between direct and indirect impacts. Direct impacts act immediately on organisms or ecosystems — hunting, habitat clearing, pollution discharge. Indirect impacts work through changes to the environment that then affect organisms — climate change affecting species ranges, acid rain killing forest trees, eutrophication depleting oxygen and killing fish. Know examples of both types for each crisis topic.
Climate Change
The Greenhouse Effect Gone Wrong🌡️ The Natural vs Enhanced Greenhouse Effect
The natural greenhouse effect is essential for life — without it, Earth's average temperature would be -18°C instead of +15°C. Greenhouse gases (CO₂, H₂O vapour, CH₄, N₂O) in the atmosphere absorb outgoing infrared radiation and re-radiate it back to Earth, keeping it warm.
The enhanced greenhouse effect is the human-caused intensification of this natural process. Burning fossil fuels, deforestation, and agriculture have increased atmospheric CO₂ from ~280 ppm (pre-industrial) to over 420 ppm today — a level not seen for at least 3 million years.
The Mechanism
How the Enhanced Greenhouse Effect Works
Step by step — from burning fossil fuels to rising sea levels.
1
Fossil fuels burned — coal, oil, and natural gas are combusted for energy, releasing CO₂ stored underground for millions of years into the atmosphere. Deforestation also releases stored carbon and removes CO₂-absorbing trees.
2
CO₂ accumulates — atmospheric CO₂ concentration rises. CO₂ absorbs infrared (heat) radiation emitted by Earth's surface that would otherwise escape to space.
3
More heat trapped — CO₂ and other greenhouse gases re-radiate absorbed heat in all directions, including back toward Earth's surface. Average global temperature rises.
4
Cascading consequences — ice caps and glaciers melt → sea levels rise; weather patterns shift → more extreme events; ocean absorbs CO₂ → ocean acidification; ecosystems disrupted → species range shifts, extinctions.
Key Gases
Greenhouse Gases — Sources & Potency
CO₂ is not the most potent — but it is the most abundant. Know all the major gases.
| Gas | Main Human Sources | Global Warming Potential | Atmospheric Lifetime |
|---|---|---|---|
| Carbon dioxide (CO₂) | Burning fossil fuels, deforestation, cement production | 1 (reference) | Centuries to millennia |
| Methane (CH₄) | Livestock digestion, rice paddies, landfills, natural gas leaks | ~80× CO₂ over 20 years | ~12 years |
| Nitrous oxide (N₂O) | Agricultural fertilisers, livestock waste, combustion | ~270× CO₂ | ~110 years |
| Ozone (O₃) | Secondary pollutant from vehicle/industrial emissions reacting in sunlight | Significant warming effect | Days to weeks (tropospheric) |
| Water vapour (H₂O) | Evaporation increases as temperatures rise — positive feedback loop | Most abundant GHG naturally; amplifies warming | ~9 days |
Consequences
Effects of Climate Change on Ecosystems
Not just hotter weather — the impacts ripple through every ecosystem on Earth.
🧊 Physical Changes
- Rising sea levels — thermal expansion of water + melting ice; threatens coastal ecosystems and human settlements
- More frequent and intense extreme weather events (droughts, floods, heatwaves, storms)
- Melting permafrost — releases stored methane (positive feedback)
- Ocean acidification — CO₂ dissolves in seawater forming carbonic acid; threatens coral reefs and shellfish
- Changing precipitation patterns — some areas drier, some wetter
🦁 Biological Changes
- Species range shifts — animals and plants moving poleward or to higher altitudes as temperatures rise
- Phenological mismatches — e.g. flowers blooming before pollinators emerge; birds hatching when insect food peak has passed
- Coral bleaching — warmer oceans cause corals to expel symbiotic algae; mass die-offs
- Increased disease spread — warmer conditions allow pathogens/vectors (e.g. malaria mosquitoes) to expand range
- Increased extinction risk for species with narrow temperature tolerance or limited dispersal ability
📌 Ozone Layer vs Greenhouse Effect — NOT the Same
Two completely separate issues, frequently confused in exams. Greenhouse effect: CO₂ and CH₄ in the lower atmosphere (troposphere) trap heat → global warming. Ozone depletion: CFCs destroy ozone in the upper atmosphere (stratosphere) → increased UV radiation reaching Earth's surface → skin cancer, eye damage, harm to phytoplankton. They have different causes, different gases, and different effects. Climate change does not cause ozone depletion and vice versa (though they interact).
Biodiversity Loss
The Sixth Mass Extinction🦋 What We Are Losing — and Why It Matters
Biodiversity refers to the variety of life at three levels: genetic diversity (variation within species), species diversity (number of different species), and ecosystem diversity (variety of habitats and communities). Current extinction rates are estimated at 100–1000 times the natural background rate — making this the sixth mass extinction in Earth's history, and the first caused by a single species.
Leading Cause
Habitat Destruction & Fragmentation
The single biggest driver of biodiversity loss worldwide — removing or dividing the spaces species need to survive.
🏗️ Habitat Destruction
- Clearing land for agriculture (especially livestock and soy), urban expansion, mining, logging
- Draining wetlands for farmland
- Tropical deforestation — most biodiverse ecosystems on Earth being cleared at ~10 million ha/year
- Destroys not just individual species but entire ecological communities and the services they provide
- Species with large home ranges (lions, elephants, leopards) are most severely affected
🔀 Habitat Fragmentation
- Large continuous habitat divided into smaller isolated patches by roads, farms, urban areas
- Small patches support fewer species and smaller populations
- Small isolated populations are vulnerable to inbreeding, genetic drift, local extinction
- Animals cannot move between patches for food, mates, or seasonal migration
- Wildlife corridors are a conservation response — strips of habitat connecting fragments
Multiple Threats
Other Major Drivers of Biodiversity Loss
HIPPO — the acronym summarising the five main threats to biodiversity.
| HIPPO | Threat | How It Causes Loss | SA Example |
|---|---|---|---|
| H | Habitat loss and degradation | Removes living space, food, breeding sites | Fynbos cleared for wheat farming in the Western Cape |
| I | Invasive species | Outcompete, prey on, or transmit disease to native species | Black wattle and Port Jackson invading fynbos; trout in mountain streams killing indigenous fish |
| P | Pollution | Toxins, eutrophication, plastic, noise/light pollution harm organisms directly and indirectly | Agricultural runoff causing algal blooms and fish kills in the Vaal and Crocodile rivers |
| P | Population growth (human) | More people = more resource extraction, land conversion, waste, energy use | Urban expansion around Cape Town threatening Cape Floral Kingdom |
| O | Overharvesting | Removing individuals faster than populations can reproduce | Abalone poaching on the Western Cape coast; rhino poaching for horn |
⚠️ Exam Watch — Why Biodiversity Loss Matters
Biodiversity has three categories of value: Direct use value — food, medicine, timber, tourism (e.g. 25% of Western pharmaceuticals are derived from tropical plants). Indirect use value — ecosystem services: pollination, water purification, flood control, climate regulation, soil formation. Intrinsic value — species have a right to exist regardless of human benefit. Examiners may ask you to argue for biodiversity conservation using any of these categories.
Focus: South Africa
Invasive Alien Species in SA
South Africa has one of the world's worst invasive species problems — threatening the Cape Floral Kingdom and water security simultaneously.
🌿 Why Invasives Are So Damaging
- Arrive without their natural predators, diseases, or competitors from their home range
- Reproduce rapidly and dominate resources
- Outcompete native species that evolved without these pressures
- Can fundamentally alter ecosystem structure and function
- Some are near-impossible to eradicate once established
🇿🇦 SA Examples
- Black wattle (Acacia mearnsii) — uses far more water than fynbos; depletes streams and groundwater; forms dense thickets
- Port Jackson (Acacia saligna) — invades fynbos; fire-adapted and hard to control
- Lantana camara — toxic to livestock; smothers native vegetation
- Bass and trout in river systems — prey on indigenous fish and frogs
- Argentine ant — displaces fynbos ants that are essential seed dispersers for proteas and ericas
Pollution & Resource Depletion
Toxins, Nutrients & Waste☁️ When Too Much of Anything Becomes a Problem
Pollution occurs when substances or energy are introduced into the environment at levels that cause harm to living organisms or disrupt natural processes. Pollution can be chemical (heavy metals, pesticides, oil), biological (sewage, pathogens), or physical (noise, light, heat, plastic). Understanding specific types of pollution — especially eutrophication, acid rain, and plastic pollution — is key exam content.
Water Pollution
Eutrophication
Too many nutrients → algal bloom → oxygen crash → aquatic dead zone. A chain reaction in slow motion.
1
Nutrient input — excess nitrates and phosphates enter water bodies from agricultural fertiliser runoff, sewage effluent, and detergents.
2
Algal bloom — nutrients cause explosive growth of algae and cyanobacteria on the water surface. Water turns green/brown. Light cannot penetrate to deeper plants.
3
Plant death — submerged aquatic plants die due to lack of light. This removes another oxygen source and adds to organic matter.
4
Decomposer explosion — aerobic bacteria decompose the dead algae and plants. Bacterial populations explode, consuming vast amounts of dissolved oxygen in the water.
5
Hypoxia / dead zone — dissolved oxygen levels drop to near zero (hypoxia). Fish and other aerobic organisms suffocate and die. Only anaerobic organisms survive. The area becomes a biological dead zone.
📌 BOD — Biological Oxygen Demand
BOD (Biological Oxygen Demand) is the amount of oxygen consumed by microorganisms decomposing organic matter in a water sample over a set time period. High BOD = lots of organic pollution = decomposers using lots of oxygen = low dissolved oxygen = poor water quality. BOD is used as a measure of water pollution. Clean water has low BOD; heavily polluted water has high BOD.
Air Pollution Consequence
Acid Rain
Burning fossil fuels releases SO₂ and NOₓ — these dissolve in rainwater to form sulphuric and nitric acid.
⚗️ The Chemistry
- Normal rain is slightly acidic (pH ~5.6) due to dissolved CO₂ forming weak carbonic acid
- Burning coal and oil releases sulphur dioxide (SO₂)
- Vehicle and industrial combustion releases nitrogen oxides (NOₓ)
- In the atmosphere: SO₂ + H₂O → sulphurous/sulphuric acid; NOₓ + H₂O → nitric acid
- Acid rain can reach pH 4 or lower — 10× more acidic than normal rain
🌲 Effects of Acid Rain
- Acidifies lakes and rivers → kills fish, amphibians, and aquatic insects
- Leaches nutrients (calcium, magnesium) from soil → weakens and kills trees
- Damages leaf surfaces → reduces photosynthesis; increases vulnerability to disease
- Dissolves limestone and marble in buildings and monuments
- SA context: Mpumalanga coal power stations are among the world's worst SO₂ sources
Persistent Pollutant
Plastic Pollution & Biomagnification
Plastic never fully breaks down — it fragments into microplastics that enter food chains and concentrate up them.
🔬 Microplastics
- Plastics fragment into microplastics (less than 5mm) and nanoplastics over time but do not biodegrade
- Found in oceans, rivers, soil, air, drinking water, and human blood
- Ingested by zooplankton, fish, seabirds, whales
- Carry absorbed toxic chemicals (PCBs, pesticides) into organisms
- ~8 million tonnes of plastic enter the ocean annually
📈 Biomagnification
- Toxic, fat-soluble substances (DDT, mercury, PCBs) that do not break down accumulate in body fat
- Bioaccumulation — build-up within a single organism over its lifetime
- Biomagnification — concentration increases at each successive trophic level
- Top predators (sharks, eagles, killer whales, humans) accumulate the highest concentrations
- Classic example: DDT — caused eggshell thinning in eagles and peregrine falcons → population collapse
Responses & Solutions
What Can Be Done🌱 From Problem to Response
Environmental crises are human-caused — which means they can be addressed through human choices and actions. Solutions operate at multiple levels: individual behaviour, technological innovation, business practice, and government policy. Understanding the range of responses — and their limitations — is important both for exams and for informed citizenship.
Biodiversity Solutions
Conservation Strategies
In-situ and ex-situ conservation — protecting species in the wild and in captivity.
🌿 In-situ Conservation (In the Wild)
- Protecting habitats where species naturally occur
- National parks, nature reserves, marine protected areas (MPAs)
- Wildlife corridors connecting fragmented habitats
- Legislation — CITES (international trade bans), national endangered species acts
- Community-based conservation — local communities as stewards
- Invasive species removal programmes (Working for Water in SA)
🏛️ Ex-situ Conservation (Away from Natural Habitat)
- Zoos, botanical gardens, aquaria — maintain populations and enable breeding programmes
- Seed banks — Svalbard Global Seed Vault stores seeds of thousands of crop varieties
- Captive breeding — southern white rhino rescued from near extinction; Arabian oryx reintroduced
- Cryopreservation of genetic material — insurance against extinction
- Limitation: cannot maintain ecological interactions; reintroduction is complex
Climate Solutions
Reducing & Adapting to Climate Change
Mitigation reduces the cause; adaptation manages the consequences. Both are needed.
⚡ Mitigation (Reducing Emissions)
- Transition to renewable energy — solar, wind, hydroelectric, geothermal
- Energy efficiency — better insulation, LED lighting, efficient vehicles
- Reforestation and afforestation — restoring carbon sinks
- Reducing methane from agriculture (diet shifts, waste management)
- Carbon pricing/taxes — making fossil fuel use economically costly
- International agreements — Paris Agreement (limit warming to 1.5–2°C)
🛡️ Adaptation (Managing Consequences)
- Sea walls and flood defences for coastal communities
- Drought-resistant crop varieties for changing rainfall patterns
- Early warning systems for extreme weather events
- Urban heat island reduction — green roofs, urban forests
- Water conservation infrastructure as rainfall patterns change
- Assisted migration of species to new suitable habitats
📌 Sustainable Development — The Key Concept
Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs (Brundtland Commission, 1987). It balances three pillars: environmental sustainability (protecting ecosystems), economic development (reducing poverty), and social equity (fairness). Sustainability is the overarching framework for all environmental solutions.
🎯 Planet Under Pressure Assessment
Eight questions on human impact and environmental crises.
Question 1 of 8
Explain the difference between the natural greenhouse effect and the enhanced greenhouse effect. Why is the enhanced greenhouse effect a problem?
Question 2 of 8
Describe the sequence of events that leads from agricultural fertiliser runoff to a dead zone in a river. What is this process called?
Question 3 of 8
DDT (a pesticide) is present in very low concentrations in water, but is found at extremely high concentrations in top predators like fish-eating eagles. What processes explain this?
Question 4 of 8
Why does acid rain form, and what are TWO effects it has on ecosystems?
Question 5 of 8
What is the difference between in-situ and ex-situ conservation? Give ONE example of each.
Question 6 of 8
What does HIPPO stand for, and why is it a useful framework for discussing biodiversity loss?
Question 7 of 8
Invasive alien species are considered a major threat to biodiversity. Why are they often so successful in their new environments?
Question 8 of 8
What is sustainable development, and why is it considered the key framework for addressing environmental crises?