IB Group 4 · Sciences
Environmental Systems and Societies
2026 syllabus · First assessment 2026
Eight topics built on the guide’s understandings, plus the three HL lenses. Each note is tied to exactly what the syllabus says you must know, with the SL core and HL-only content clearly split.
T1. Topic 1: Foundation
The three key concepts that frame the whole course: perspectives, systems and sustainability.
ES1.1 — Perspectives
Perspectives, values and worldviews — What a perspective is, the factors that inform it, and how values and worldviews underpin it.
Environmental value systems and worldview categories — The EVS model (inputs, values, outputs) and the technocentric, anthropocentric and ecocentric spectrum.
Investigating and tracking perspectives — Values surveys and behaviour-time graphs: the two syllabus skills for studying perspectives empirically.
The environmental movement — The seven categories of influence that have shaped the movement, one example needed from each.
ES1.2 — Systems
Systems and the systems approach — Systems, storages and flows, the diagram convention, and the difference between transfers and transformations.
Open and closed systems, Earth and scale — What crosses a boundary, Earth as one integrated system (Gaia), and applying the concept from a bromeliad to the globe.
Feedback loops and equilibrium — Stabilizing negative feedback, amplifying positive feedback, and the equilibria they maintain or disrupt.
Tipping points and regime shifts — How positive feedback drives a system past a threshold into a new stable state.
Models and emergent properties — Models as simplified reality, the accuracy lost in simplification, and properties that arise only from interaction.
Resilience of systems — How diversity and storage size build resilience and set response times, and how humans erode it.
ES1.3 — Sustainability
Sustainability and its three pillars — Defining sustainability and the environmental, social and economic pillars, with strong versus weak models.
Sustainable development and its limits — The Brundtland definition, ecosystem collapse from overuse, and why GDP can mislead.
Environmental justice and scale — The right to a clean environment and fair access, how inequality drives disparities, and the operating scales involved.
Measuring sustainability: indicators and footprints — Sustainability indicators, ecological, carbon and water footprints, biocapacity and citizen science.
Sustainability frameworks and models — The SDGs, planetary boundaries, doughnut economics and the circular economy, each with uses and limitations.
HL: quantifying planetary boundaries — Using quantitative data on control variables to judge when and if a planetary boundary has been crossed.
T2. Topic 2: Ecology
How ecosystems work: populations and communities, energy and biomass, biogeochemical cycles, climate and biomes, and change over time.
ES2.1 — Individuals, populations, communities, and ecosystems
The biosphere, species and classification — The nested hierarchy of life, the biological species concept, binomial naming, and the tools taxonomists use to identify organisms.
Populations, niches and interactions — What a population is, the abiotic and biotic factors that shape distribution, the niche concept, and the six ways populations interact.
Population dynamics and human populations — Carrying capacity, density-dependent regulation and negative feedback, J- and S-curves, and why human carrying capacity is hard to assess.
Estimating abundance: sampling methods — Random, systematic and transect sampling; quadrats for non-mobile organisms; and capture-mark-release-recapture with the Lincoln index.
Communities, ecosystems and sustainability — Defining community, habitat and ecosystem, then sustainability, tipping points, keystone species and the biosphere-integrity boundary.
HL: Clades, realized niches and life cycles — Clades versus the traditional hierarchy, fundamental versus realized niche, r- and K-strategists, and reading human impact from life cycles.
ES2.2 — Energy and biomass in ecosystems
The laws of thermodynamics and two key processes — Energy and matter as ecosystem inputs, the first and second laws, and how photosynthesis and cellular respiration transform them.
Producers, consumers and food chains — Autotrophs and heterotrophs, the range of consumer strategies, and how energy and biomass flow along food chains and webs.
Energy losses, productivity and ecological pyramids — Why transfer is never complete, gross and net productivity, the 10% rule, measuring biomass, and pyramids of number, biomass and energy.
Pollutants and human impacts on energy flow — Bioaccumulation and biomagnification, microplastics as carriers, and how fossil fuels, deforestation, urbanization and agriculture disrupt flows.
HL: Chemoautotrophs and measuring productivity — Photoautotrophs versus chemoautotrophs, and defining and measuring primary and secondary productivity from lab and field data.
HL: Sustainable yield, efficiency and entropy — NPP as the basis for food chains, maximum sustainable yields, ecological efficiency calculations, and entropy in ecosystems.
ES2.3 — Biogeochemical cycles
Stores, sinks, sources and the carbon cycle — How cycles keep elements available, the store/sink/source distinction, residence time, and the flows that move carbon between stores.
Carbon, oceans and human impact — Agricultural soils as sinks or sources, ocean uptake and acidification, and at least three measures to alleviate human effects on the carbon cycle.
The nitrogen cycle — Organic and inorganic nitrogen stores, the essential bacterial processes, denitrification in anaerobic soils, and mutualistic nitrogen fixation.
Nitrogen: human impact and the planetary boundary — How human activities and the Haber process alter the cycle, why the nitrogen planetary boundary is crossed, and the collaboration needed.
HL: Lithosphere carbon stores and methane — Long-residence carbon in rocks and fossil fuels, limestone from marine hard parts, fossil-fuel formation, and methane from methanogenic bacteria.
ES2.4 — Climate and biomes
Climate, weather and the distribution of biomes — Climate versus weather, what a biome is, and how temperature, precipitation and insolation determine which biome develops.
Atmospheric circulation, oceans and shifting biomes — The tricellular model and latitude, how oceans and currents distribute heat, and the poleward, upslope shift of biomes under warming.
HL: Climate types and biome development — The three general climate types linked to biomes, and why the predicted biome may not develop because of secondary or human influences.
HL: ENSO and tropical cyclones — The El Nino Southern Oscillation, how El Nino and La Nina develop and affect climate and productivity, and warming-driven cyclone intensity.
ES2.5 — Zonation, succession and change in ecosystems
Zonation along environmental gradients — Zonation as spatial change in community, and using transects and kite diagrams to link species distribution to abiotic variables.
Succession: seres, primary and secondary — Succession as change over time, how each seral community makes way for the next, and named primary and secondary examples.
Change through succession: diversity and resilience — How energy flow, productivity, diversity, soil and nutrient cycling shift over succession, and how diversity underpins resilience and stability.
HL: Controls on succession and productivity — Climatic, geological and top-down controls on the final community, how GP and NP change through succession, and r- and K-strategists.
HL: Challenging the climax community — The contested idea of a single natural climax, the Vera hypothesis and alternative stable states, and human-driven plagioclimax.
T3. Topic 3: Biodiversity and conservation
What biodiversity is and how it evolves, human impacts on it, and how it is conserved and regenerated.
ES3.1 — Biodiversity and evolution
Biodiversity and its three levels — Biodiversity as the total diversity of living systems at habitat, species and genetic levels, and how each contributes to resilience.
Evolution, natural selection and speciation — Evolution as cumulative heritable change, the mechanism of natural selection, and how isolation generates new species.
Quantifying species diversity — Richness and evenness, and Simpson's reciprocal index for comparing ecosystems and monitoring change over time.
Knowing biodiversity for management — Why global and regional knowledge is needed for conservation, and how it is gathered from citizen science to parabiologists.
HL: Genetic diversity, isolation and human-driven change — Mutation and sexual reproduction, reproductive isolation and hotspots, and how human activity reshapes selection.
HL: Geological time and the Anthropocene — Deep time and fossils, epochs and mass extinctions, and the debated case for a human-defined geological epoch.
ES3.2 — Human impact on biodiversity
Direct and indirect threats — How direct and indirect human influences reduce biodiversity, and how multiple impacts amplify one another.
Invasive alien species — How invasive species arrive, increase and reduce local biodiversity through competition, predation and disease, with a local example.
The IUCN Red List and conservation priorities — How the IUCN assesses conservation status, and how status publicizes vulnerability and shapes priorities for governments, NGOs and citizens.
Named species and the tragedy of the commons — Three named species case studies and the tragedy of the commons as a model of shared resource overexploitation.
HL: Hotspots, KBAs and conservation conflict — Threats to tropical hotspots, how Key Biodiversity Areas are prioritized, and the conflict between exploitation and conservation.
HL: Indigenous justice and biosphere integrity — Traditional indigenous land management under pressure, environmental justice in conservation, and the biosphere-integrity planetary boundary.
ES3.3 — Conservation and regeneration
Why and how we conserve — Arguments for preservation, and the ex situ, in situ and mixed strategies used to act on them.
Treaties, habitats and reserve design — The Convention on Biological Diversity, habitat protection and active management, and how the size and shape of reserves affect biodiversity.
Rewilding and the planetary boundary — Regenerating natural processes through rewilding, and using conservation at all levels to stay within the biodiversity planetary boundary.
Worldviews and value systems — How ecocentric versus anthropocentric and technocentric perspectives shape conservation choices, and what makes strategies succeed.
HL: Organizations, feedback and rewilding trade-offs — What determines organizations' success, how restoration triggers positive feedback loops, and the benefits and limitations of rewilding.
HL: Assessing success and ecotourism — Judging conservation success at three levels, and how ecotourism can both help and harm communities and ecosystems.
T4. Topic 4: Water
Water systems, access and security, aquatic food production, and water pollution.
ES4.1 — Water systems
Drivers and the cycle as a system — Solar radiation and gravity drive water movement; the global hydrological cycle modelled as stores (boxes) and flows (arrows).
Stores and flows — The six main stores and their relative proportions, and the thirteen named flows that transfer water between them.
Human impacts and steady state — How agriculture, deforestation and urbanization alter flows and stores, and using input/output diagrams to find sustainable harvest rates.
Life-supporting properties of water — Polarity, cohesion, adhesion, solvent action, transparency, specific heat capacity, temperature-dependent density and gas solubility.
Oceans as a carbon sink — How oceans absorb and sequester atmospheric CO2, the short-term acidification pathway and the long-term seabed-biomass pathway.
Stratification, upwelling and circulation — Thermal stratification and the thermocline, why warming intensifies it, upwelling, and the thermohaline ocean conveyor belt.
ES4.2 — Water access, use and security
Water security, access and rising demand — Defining water security, the social/cultural/economic/political factors shaping access, and why growth and development raise demand.
Scarcity, stress and their causes — Physical vs economic scarcity, water stress and the 1,700 m3/yr/capita threshold, socio-economic causes and transboundary disputes.
Increasing supply and its impacts — Methods of boosting supply and industrial strategies to address stress, weighed against environmental impacts that can be reduced but not eliminated.
Conservation and mitigation — Domestic conservation techniques, industrial and food-production strategies, and a named country's mitigation of water scarcity.
Equity and citizen science — How inequitable access to water and sanitation harms health and development, and the role of citizen science in monitoring water.
Planetary boundary, governance and footprints — Freshwater use as a planetary boundary, the governance needed for sustainable use, and water footprints as a measure.
ES4.3 — Aquatic food production systems
Aquatic producers and rising demand — Phytoplankton and macrophytes as the base of aquatic food webs, the organisms humans eat, and why demand is increasing.
Overexploitation and fishery collapse — Destructive harvesting methods and how overexploitation has collapsed fisheries such as the Grand Banks cod.
Maximum sustainable yield and climate stress — MSY and the yield/fishing-effort graph for setting quota caps, plus climate change and ocean acidification stressing ecosystems.
Managing exploitation: policy, MPAs, aquaculture — Policy and consumer measures, marine protected areas, and aquaculture's expansion weighed against its environmental impacts.
Productivity, stock assessment and MSY risks — How productivity links to stratification and nutrients, measuring fish stocks and harvest rates, and the risks of fishing at MSY.
Recovery, UNCLOS and marine mammal ethics — Stakeholder cooperation to restore stocks, the UNCLOS exclusive economic zone and high seas, and the ethics of hunting marine mammals.
ES4.4 — Water pollution
Sources of pollution and plastics — The multiple sources of water pollution and the accumulation of plastic debris and microplastics in marine environments.
Measuring water quality and BOD — The chemical, physical and biological parameters that define water quality, and biochemical oxygen demand as an indirect measure of organic matter.
Eutrophication and its management — How nutrient inputs cause algal blooms, the oxygen-depletion cascade with positive feedback, and the three levels of management.
Pollutants, harmful algal blooms and dead zones — The range of water pollutants, harmful algal blooms and their toxins, and why anoxic dead zones are becoming more frequent.
Treatment, indicators and quality indices — Primary/secondary/tertiary sewage treatment, indicator species, biotic indices and the water quality index.
Standards and citizen action — WHO guidelines and statutory standards, and the actions individuals and citizen groups take to reduce water pollution.
T5. Topic 5: Land
Soil as a system, and agriculture and food production.
ES5.1 — Soil
Soil as a dynamic system — Soil as a system with its own components and organisms, and the layered profile that develops over time.
Inputs, outputs, transfers and transformations — What enters and leaves the soil system, the flows within it, and how to draw it as a systems diagram.
Soil in ecosystems: growth, biodiversity and carbon — Soil as the foundation for plant growth and biodiversity, its role in element cycles, and as a carbon sink, store or source.
Soil texture and primary productivity — How the mix of sand, silt, clay and humus is defined and measured, and how it controls productivity.
HL: Profiles, horizons and soil formation — Classifying soils by profile, the O, A, B and C horizons, the value of the A horizon, and the five formation factors.
HL: Particle properties, soil analysis and carbon release — Sand, silt and clay chemistry (CEC), the properties used to characterise a soil, and how soils release carbon.
ES5.2 — Agriculture and food
Feeding a growing, unequal world — Finite land and a rising population, the vulnerability of marginalized groups, food waste and distribution, and food security.
Agricultural systems: variation and classification — Why systems vary with soil and climate, how they are classified, and traditional low-density techniques.
The Green Revolution and sustaining soil — The Green Revolution and its consequences, alternatives to synthetic fertilizer, and the full soil-conservation toolkit.
Sustainable diets and food strategies — Why lower-trophic-level diets are more sustainable and the current global strategies for a sustainable food supply.
HL: Contrasting choices and alternative farming — Soil- and climate-driven farming choices, alternative approaches, regenerative and permaculture methods, and high-tech production.
HL: Diet sustainability, wild harvesting and malnutrition — What makes a diet sustainable, harvesting wild species, evaluating low-productivity systems, and the causes of malnutrition and famine.
T6. Topic 6: Atmosphere and climate change
The atmosphere, the causes and impacts of climate change, mitigation and adaptation, and stratospheric ozone.
ES6.1 — Introduction to the atmosphere
The atmosphere and its circulation — The atmosphere as the boundary of the biosphere, a mixture of gases redistributed by wind, and the tricellular model that moves heat from equator to poles.
Greenhouse gases and aerosols — The five named GHGs and aerosols that absorb and re-emit infrared radiation, the most abundant ones, and why water vapour is left out of climate models.
The greenhouse effect and key terms — How the greenhouse effect keeps Earth warm enough for life, and how greenhouse effect, enhanced greenhouse effect, global warming and climate change differ.
A dynamic atmosphere and thinning with altitude — The atmosphere as the product of continuous physical and chemical processes, gravity holding gases near the surface, and the standard lapse rate.
Milankovitch cycles and the Quaternary — Three orbital cycles driving glacial-interglacial climate through feedback, and how current warming is pushing Earth out of the Quaternary into the Anthropocene.
Life and atmospheric composition — The two-way relationship in which photosynthesis reshaped the early atmosphere, enabling ozone formation and metal oxidation, which in turn shaped evolving life.
ES6.2 — Climate change: causes and impacts
Climate, rising CO₂ and proxy evidence — Climate as typical atmospheric conditions, the accelerating anthropogenic rise in CO₂ since the Industrial Revolution, and the ice-core, tree-ring and sediment record.
Enhanced greenhouse effect and its impacts — How anthropogenic GHGs enhance the greenhouse effect, and the resulting impacts on ecosystems (local to global) and on societies.
Feedback loops, planetary boundary and perspectives — Systems diagrams with positive and negative feedback, evidence the climate-change planetary boundary is passed, and why perspectives on climate change differ.
Measuring and modelling climate — Direct and indirect (proxy) data sources, global climate models built from equations, hindcasting to test validity, and the use of scenarios.
Tipping points and tipping cascades — Critical thresholds that shift the climate to a new equilibrium, named examples driven by positive feedback, and how interacting tipping points cascade.
Responsibility, vulnerability and climate justice — How countries differ in responsibility and vulnerability, using per-person and cumulative emissions, and the equity and climate-justice implications.
ES6.3 — Climate change: mitigation and adaptation
Global action and decarbonization — Why avoiding catastrophic change needs coordinated global action rather than isolated states, and what decarbonization and carbon neutrality mean.
Mitigation strategies — The three categories of mitigation, reducing the process of warming, reducing GHG production, and removing CO₂, with at least two examples of each.
Adaptation strategies and plans — Structural and non-structural adaptation with examples, plus adaptation plans such as NAPAs and the role of the UN Development Programme.
Responses, the UN and IPCC scenarios — Government and non-governmental responses across four levers, the UNFCCC-IPCC-COP framework and the Kigali Amendment, and the IPCC emissions scenarios.
Technology, barriers and geoengineering — Technologies that aid mitigation, the five barriers to implementing climate strategies, and geoengineering weighed for and against.
Perspectives, stakeholders and the commons — How stakeholders shift perspectives, why views on urgency vary between groups, and the tragedy of the commons applied to the shared atmosphere.
ES6.4 — Stratospheric ozone
Solar radiation and the danger of UV — The Sun's electromagnetic spectrum, why shorter-wavelength UV carries more energy, and how stratospheric ozone absorbs all UVC and most UVB.
Impacts of UV and the ozone equilibrium — UV harm to phytoplankton, DNA and human health, the steady-state equilibrium of ozone formation and destruction, and how ODSs tip it.
Ozone depletion impacts and the Montreal Protocol — Rising surface UVB and polar ozone holes, and the Montreal Protocol as the most successful example of international environmental cooperation.
Ozone chemistry: equations and halogens — The chemical equations for ozone formation and destruction, how halogens from ODSs break down ozone, and why polar depletion peaks in spring.
HFCs, the Kigali Amendment and air conditioning — HFCs as ozone-friendly but potent greenhouse gases controlled by the Kigali Amendment, and the energy and refrigerant issues of air conditioning.
T7. Topic 7: Natural resources
Natural resources and their management, energy sources, and solid waste.
ES7.1 — Natural resources: uses and management
Natural resources, capital and income — Resources as raw materials and energy; natural capital as the stock, natural income as the goods and services it yields, and what framing nature this way implies.
Ecosystem services, renewability and value — Life-supporting ecosystem services, the renewable/non-renewable split, and the nine value types of natural capital, whose value is dynamic.
Managing use: sustainability, security and choice — Why natural capital must be managed, what resource security means, and the factors and perspectives shaping a society's resource choices.
HL: Managing and intervening in resource use — Government, NGO and social-movement strategies that steer use of natural capital, and how the SDGs frame sustainable resource management.
HL: Environmental impact assessments — How an EIA addresses sustainability in development projects, how guidance varies by country, and how public EIAs give citizens a stakeholder role.
HL: Resource insecurity and security — Unsustainable extraction, short-term economic pressure, the causes and consequences of resource insecurity, and how security can be improved.
ES7.2 — Energy sources: uses and management
Energy sources and rising consumption — Renewable and non-renewable sources, most output converted to electricity, and why global energy demand keeps rising while fossil fuels dominate.
Sustainability and energy choices — How the sustainability of sources varies, the environmental cost of every source including restoration, and the factors behind a country's energy choices.
Storage, conservation and efficiency — Why intermittent renewables need storage, the peak-shaving solutions available, and how conservation and efficiency cut dependence on imports.
HL: Energy security and fossil fuels — What energy security means and how it is improved, and the global economy's dependence on finite reserves of coal, oil and natural gas.
HL: Nuclear power and battery storage — Nuclear as a non-renewable low-carbon source with its trade-offs, and the impacts of the large-scale battery storage needed to cut carbon emissions.
ES7.3 — Solid waste
Waste: sources, types and content — Classifying waste by source and by type, and the diverse content of solid domestic waste.
What shapes waste, and where its impacts fall — The factors driving variation in waste volume and composition, and how impacts can be felt far from where waste was generated.
Pollution and waste-management strategies — When absorbed waste becomes pollution, the role of biodegradability and half-lives, and why preventative strategies beat restorative ones.
Disposal options and promoting sustainability — The advantages and disadvantages of the main disposal options, and the strategies that promote sustainable management of solid domestic waste.
The circular economy — A holistic perspective on waste, tracing a resource from manufacture through to appropriate product recovery.
T8. Topic 8: Human populations and urban systems
Human population dynamics, urban systems and planning, and urban air pollution.
ES8.1 — Human populations
Inputs, outputs and population rates — Births and immigration as inputs, deaths and emigration as outputs, and the rates that quantify a population: crude rates, total fertility rate, life expectancy, doubling time and natural increase.
Predicting future global growth — The rapid growth curve of the human population and how UN models predict its future through three fertility-linked scenarios, with the uncertainty behind them.
Managing growth: direct and indirect policies — Direct anti-natalist, pro-natalist and migration policies, plus indirect economic, social, health and development policies, with named examples.
Population structure: age-sex pyramids and the DTM — Modelling population composition with age-sex pyramids and the five stages of the demographic transition model.
HL: Population pressure, dependency and momentum — How rapid growth stresses Earth's systems, and how pyramids reveal the dependency ratio and population momentum.
HL: Comparing countries and environmental migration — Explaining structure and growth using two countries at different DTM stages, and migration driven by climate change and land degradation.
ES8.2 — Urban systems and urban planning
Urban ecosystems and the urban system — Urban areas as ecosystems with biotic and abiotic components, what defines an urban area against a rural one, and the urban area as an interconnected system.
Urbanization, suburbanization and their impacts — Rural-to-urban migration and its push-pull drivers, suburbanization and urban sprawl, and the environmental changes urban expansion brings.
Urban planning and sustainability — The purpose of urban planning for all stakeholders, and the factors and named examples of sustainable urban planning.
Ecological urban planning — A holistic approach treating the urban system as an ecosystem, across five categories from urban ecology to regenerative architecture.
HL: Compactness, mixed use and social mix — The principles of compact, mixed-use, socially mixed cities, their sustainable advantages, and green-space access as environmental justice.
HL: Circular economy, doughnut models and green architecture — Circular economy and doughnut economics models applied to cities, and green architecture using environmentally friendly materials and practices.
ES8.3 — Urban air pollution
Urban air pollutants: primary and secondary — The main pollutants from human activity, the PM2.5 and PM10 size classes, natural and anthropogenic sources, and the split between primary and secondary pollutants.
Managing urban air pollution — Management and intervention strategies that reduce urban air pollution, from public transport to catalytic converters.
Acid rain: formation, impacts and management — The chemistry that turns NOx and sulfur dioxide into acid rain, its impacts on ecology, humans and buildings, and strategies to reduce it.
HL: Photochemical smog — How sunlight turns NOx and VOCs into PANs and tropospheric ozone, and the meteorological and topographical factors, including temperature inversion, that intensify it.
HL: Impacts of tropospheric ozone — The direct biological and physical impacts of tropospheric ozone and its indirect societal and economic costs, borne unequally.
HL. HL lenses (higher level only)
The three higher-level lenses applied across the course: environmental law, economics and ethics.
ESL.a — Environmental law
What law is, and what environmental law is — Law as enforced rules of human behaviour, and environmental law as the rules governing our use and impact on natural resources, across four domains.
Justice, enforcement and constitutionalism — How environmental law serves environmental justice, why it is hard to pass, why its success varies by country, and the rise of environmental constitutionalism.
Scales of law-making and transboundary issues — Local, national and international law-making (higher scales supersede local), and how international law tackles transboundary pollution and resource management.
International agreements, institutions and courts — Conventions versus protocols and why agreements are slow; the relative success of Montreal, Kyoto and Paris; implementing bodies (CITES, IUCN) and international courts.
Legal personhood and integrating law with economics — Granting legal personhood to natural entities, and why the most sustainable outcomes combine legal and economic strategies.
ESL.b — Environmental economics
Economics, environmental economics and market failure — Economics as the study of production, distribution and consumption; environmental economics and its technocentric/ecocentric perspectives; and market failure.
Correcting market failure: polluter-pays and greenwashing — The polluter-pays principle and its named solutions (quotas, fines, taxes, tradeable permits, certification), and greenwashing as a form of misinformation.
The commons, valuation and environmental accounting — The tragedy of the commons and how it can be circumvented (Ostrom), environmental accounting, and use versus non-use values.
Ecological economics — The economy as a subsystem of the biosphere, natural capital and the precautionary principle, and the greater emphasis on valuing ecosystem services.
Economic growth and environmental welfare — GDP and per-capita GDP, the linear economy, the mixed impacts of growth on the environment, and eco-economic decoupling (absolute vs relative).
Degrowth and sustainable economic models — The ecological-economics case for degrowth/slow/zero growth and footprint-biocapacity balancing, and the circular economy and doughnut economics models.
ESL.c — Environmental ethics
Ethics and environmental ethics — Ethics as the philosophy of right and wrong, and environmental ethics: its 1960s-70s emergence and why Western traditions were felt to be inadequate.
Beliefs about the human-nature relationship — How differing fundamental beliefs yield ecocentric, stewardship and anthropocentric/technocentric ethical positions.
Instrumental and intrinsic value — Instrumental value (usefulness to humans) and intrinsic value (worth for what a thing is), and why the two are not exclusive.
Moral standing — What it means for an entity to be morally considered, ecocentric extensions to living and non-living nature (Leopold's land ethic), and future generations.
The three traditional ethical approaches — Virtue ethics, consequentialist (utilitarian) ethics and rights-based (deontological) ethics, contrasted by their focus.
The appeal to nature, and converging justice movements — The 'appeal to nature' fallacy, and the converging goals of environmental and social justice movements.
★. Case studies
Exam-ready case studies to memorise for the Paper 2 essays, grouped by topic. Each gives the overview, a systems and sustainability angle, the management response, and an HL-lens take.
ECS.1 — Rapa Nui (Easter Island) collapse
Overview — A small, isolated Pacific island whose society is the classic cautionary tale of exceeding environmental limits.
Systems and sustainability angle — Resource depletion, positive feedback and a tipping point: an ecological footprint that outran the island's biocapacity.
The debate and the lessons — Ecocide versus external causes, and what the island teaches about sustainability.
HL lens angle — Ethics of intergenerational responsibility and the economics of a closed common-pool resource.
ECS.2 — Bhutan: Gross National Happiness
Overview — A small Himalayan kingdom that measures progress by Gross National Happiness rather than GDP alone, and constitutionally protects its forests.
Systems and sustainability angle — A national attempt to hold economy, society and environment in balance: strong sustainability, natural capital as a carbon sink, and biocapacity kept ahead of footprint.
Management and response — GNH as a policy framework, constitutional forest cover and carbon-negative status, evaluated for what works and what strains it.
HL lens angle — The economics of measuring progress beyond GDP, and the ethics of an ecocentric national worldview.
ECS.3 — Yellowstone grey wolves (trophic cascade)
Overview — Grey wolves were exterminated from Yellowstone, then reintroduced in 1995, giving a rare before-and-after test of a top predator's role.
Systems and sustainability angle — A keystone predator, top-down control and a trophic cascade: removing and restoring one species reshaped storages and flows across the whole food web.
The mechanism and lessons — How the cascade works, what the evidence does and does not show, and why keystone species matter for management.
HL lens angle — The ethics of reintroducing a predator and the economics and law of managing wolves across a working landscape.
ECS.4 — St Matthew Island reindeer (population overshoot)
Overview — 29 reindeer put on a remote Bering Sea island exploded to thousands, then crashed to near-zero in one winter: the classic overshoot experiment.
Systems and sustainability angle — Exponential J-curve growth on a closed island with no predators, overshooting a lowered carrying capacity into a boom-and-bust collapse.
The mechanism and lessons — Why the population overshot and crashed, what the data show, and what it teaches about limits and human populations.
HL lens angle — The economics of a closed common-pool resource and the ethics of overshoot as a warning for human population and consumption.
ECS.5 — Gorongosa National Park restoration (Mozambique)
Overview — A war-devastated African park rebuilt into a flagship of restoration ecology and community-linked conservation.
Systems and sustainability angle — Rewilding a collapsed ecosystem: rebuilding storages and trophic flows and letting feedbacks work in reverse.
Management and response — A public-private restoration partnership pairing wildlife recovery with human development.
HL lens angle — The economics of ecosystem services and ecotourism, and an ethic of stewardship and intrinsic value.
ECS.6 — Palm oil and the orangutan (Borneo and Sumatra)
Overview — The world's cheapest, highest-yielding vegetable oil, and the tropical forests and great apes cleared to grow it.
Systems and sustainability angle — Habitat destruction in a biodiversity hotspot, and why the highest-yield oil is a genuine sustainability dilemma.
Management and response — Certification (RSPO), moratoria and protected areas, and how far a market label can travel.
HL lens angle — Market failure and greenwashing, and the ethics of intrinsic value and moral standing for great apes.
ECS.7 — Grand Banks cod collapse (Newfoundland)
Overview — The 500-year cod fishery that crashed within a generation of industrial trawling.
Systems and sustainability angle — Maximum sustainable yield, overshoot and a positive-feedback stock collapse with a lasting regime shift.
Management and response — The 1992 moratorium: too late to prevent collapse, and slow to reverse it.
HL lens angle — The economics of a common-pool resource and the law of exclusive economic zones and quotas.
ECS.8 — The Aral Sea
Overview — How diverting two rivers for irrigation drained one of the largest lakes on Earth.
Systems and sustainability angle — A water budget forced out of steady state: inputs cut, outputs unchanged, storage and salinity spiralling.
Management and response — The Kok-Aral dam that saved the North Aral, while the South Aral was largely written off.
HL lens angle — Transboundary water law across five states, and the economics of cotton versus a vanished sea.
ECS.9 — The Dust Bowl (1930s USA)
Overview — The 1930s wind-erosion disaster on the US Southern Great Plains: the textbook case of ploughing a grassland soil system past its limits.
Systems and sustainability angle — A soil system whose outputs (wind erosion) outran its inputs, driven by a positive-feedback loop that stripped the fertile topsoil.
Management and response — The Soil Conservation Service and the conservation toolkit: shelterbelts, contour ploughing and crop rotation.
HL lens angle — The economics of a common-pool grassland: uncosted externalities and market failure on the plains.
ECS.10 — The Green Revolution (Punjab, India)
Overview — How high-yielding crops, irrigation and agrochemicals turned Punjab into India's breadbasket, and averted famine at a lasting environmental cost.
Systems and sustainability angle — An intensive agricultural system: high inputs bought high yields, but at the expense of soil, water and long-term sustainability.
Management and response — The high-yielding-variety package and price support, weighed against groundwater depletion, salinization and debt.
HL lens angle — The economics of intensification: subsidies, uncosted externalities and unequal winners.
ECS.11 — The Montreal Protocol and the ozone hole
Overview — The great environmental success story: how the world identified the ozone hole and phased out the chemicals causing it.
Systems and sustainability angle — A stratospheric equilibrium tipped by human chemicals, then allowed to recover: the planetary boundary that was not crossed.
Management and response — How the Montreal Protocol actually worked: binding phase-outs, funding for developing countries and trade rules.
HL lens angle — Environmental law in action: why this treaty succeeded where others have struggled.
ECS.12 — Tuvalu and the Maldives: climate impacts and adaptation
Overview — Two low-lying island nations on the front line of sea-level rise: least responsible for climate change, most exposed to it.
Systems and sustainability angle — How rising seas, salt water and coral loss threaten the physical basis of atoll societies, and what limits their resilience.
Management and response — Adaptation on the ground: sea walls, reclaimed land and freshwater security, and the last resort of migration.
HL lens angle — Climate justice: the ethics of responsibility, vulnerability and obligations to future generations.
ECS.13 — Chernobyl (1986)
Overview — The world's worst nuclear accident: a reactor explosion that turned a low-carbon energy source into a centuries-long contamination problem.
Systems and sustainability angle — Energy-source risk, radioactive half-lives and an exclusion zone: pollution released far faster than any ecosystem can transform it.
Management and response — Evacuation, containment and a global tightening of nuclear safety, weighed against Soviet secrecy and a permanent cost.
HL lens angle — The ethics of waste that outlives its makers, and the environmental law that grew from transboundary fallout.
ECS.14 — Amsterdam and the circular economy
Overview — The first city to adopt "doughnut economics" as policy, paired with a plan to halve its use of new raw materials by 2030.
Systems and sustainability angle — Closing material loops and staying between a social floor and an ecological ceiling: waste reframed as a resource kept in the system.
Management and response — Concrete targets and value-chain projects, weighed against the risk of an aspirational model and an offshored footprint.
HL lens angle — The circular economy and the doughnut as applied ecological economics, and a fix for the linear economy's market failure.
ECS.15 — China's one-child policy
Overview — The world's largest anti-natalist experiment: a state limit on births that reshaped a nation's age and sex structure.
Systems and sustainability angle — Population dynamics, the demographic transition and momentum: why a low fertility rate did not stop the population growing.
Management and response — Falling birth rates set against coercion, a skewed sex ratio and a rapidly ageing population.
HL lens angle — Individual reproductive rights against a collective goal, and the gendered injustice the policy left behind.
ECS.16 — Curitiba, Brazil: sustainable urban planning
Overview — A southern Brazilian city that became a global model for integrated, low-cost sustainable urban planning from the 1970s.
Systems and sustainability angle — Managing an urban system's flows: transport, land use, green space and waste designed to work together rather than in isolation.
Management and response — Bus Rapid Transit, park-based flood control and a rubbish-for-food scheme, set against sprawl and rising car use.
HL lens angle — The economics of a cheap transit system and incentive design that internalise the costs a car-based city ignores.
Full notes + a tutor for every subject
Every understanding statement above is written out in full, mapped point by point, with a tutor that answers from the syllabus. One payment — every subject, until your exams.