IB DP Environmental Systems and Societies – Natural resources, energy and solid waste Revision Notes

For full explanations and worked examples, start with the Topic 7 study guide. These notes condense Topic 7 of IB Diploma Programme Environmental Systems and Societies for the final weeks before the exam. They are aligned to the IB Environmental systems and societies subject brief, first assessment 2026, and cover syllabus sections 7.1–7.3 at SL and HL (10 and 18 teaching hours; HL students study some topics in extra depth). It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions.

Links: practice questions · ESS course hub · printable checklist · Topic 1 Foundations revision notes · ESS assessment revision notes

Key definitions

Term	Definition
Natural resource	Any part of the natural world used by humans
Natural capital	The stock of natural resources (forest, aquifer, ore body)
Natural income	The yield of goods or services the stock produces (timber growth, recharge, flood control)
Renewable natural capital	Regenerates within a human timescale if used at or below its growth rate
Non-renewable natural capital	Forms far more slowly than it is used; any extraction depletes it
Sustainable yield (SY)	The rate of increase of natural capital; the amount that can be taken without reducing the stock
Maximum sustainable yield (MSY)	The largest harvest that can be taken year after year; about half the carrying capacity for logistic growth
Tragedy of the commons	Overuse of a shared resource because each user gains the full benefit of taking more but shares the cost
Resource security	Reliable, affordable access to the resources a society needs
Energy security	Reliable, affordable access to enough energy
Energy efficiency	Getting the same output from less energy input
Energy conservation	Using less energy by changing behaviour
Solid domestic waste (SDW)	Household solid waste: organic, paper, plastics, glass, metals, textiles, e-waste
Waste hierarchy	Reduce → reuse → recycle/compost → recover energy → dispose

Formulas and data skills

What you find	How	Units
Sustainable yield	stock at t + 1 − stock at t (with no harvest)	t per year, kg per year, kJ per year
SY as a rate	SY ÷ stock × 100	% per year
Net change in stock	SY − harvest	t per year
Percentage share	part ÷ total × 100	%
Percentage change	(new − old) ÷ old × 100	%
Per capita value	total ÷ population	kg per person per year
Resource lifespan	remaining stock ÷ net annual use	years
Landfill volume	mass ÷ density	m³

Method in steps: sustainable yield from data

1. Take two stock values one time interval apart, with no harvest in between.
2. Subtract: SY = later − earlier. Give units per time.
3. Compare the harvest with SY. Harvest > SY means capital is being depleted.
4. State the assumption: growth rate stays constant (it usually falls as the stock shrinks).

Method in steps: interpreting an energy-mix table

1. Add the totals yourself; do not assume they are given correctly.
2. Group sources: fossil, nuclear, renewable. Nuclear is not renewable.
3. Give shares as percentages and changes in percentage points.
4. Separate the share from the absolute amount — a rising share can hide a flat or rising fossil total.
5. Link to energy security: imported fuels, dependence on one source, intermittency.

Small worked reminders

Percentage points. A renewable share rising from 17.9% to 30.6% is a rise of 30.6 − 17.9 = 12.7 percentage points. It is not a 12.7% rise; as a relative change it is 12.7 ÷ 17.9 × 100 = 70.9%. Say which one you mean.

Landfill lifespan. A site has 150,000 m³ of space left and receives 12,000 t of compacted waste a year at 0.8 t/m³. Volume per year = 12,000 ÷ 0.8 = 15,000 m³, so lifespan = 150,000 ÷ 15,000 = 10 years. Divide mass by density, not the other way round.

7.1 Natural resources in brief

• Resource value is dynamic: it changes with technology (lithium for batteries), culture (sacred groves), price (low-grade ore becomes worth mining) and substitution.
• Ecosystem services: provisioning (food, water, timber), regulating (flood control, pollination, climate), supporting (soil formation, nutrient cycling), cultural (recreation, spiritual value).
• Management tools: quotas, permits, protected areas, taxes and pricing, certification, community rules, circular-economy design.
• Commons can be managed well where boundaries are clear, rules are local and cheating is punished.

7.2 Energy in brief

• Non-renewable: coal, oil, natural gas, nuclear fission (uranium is a finite ore).
• Renewable: solar, wind, hydro, geothermal, tidal, wave, biomass.
• Energy choice depends on availability, technology, cost, economics, politics, culture, the environment and energy security.
• Intermittency (wind, solar) is managed by storage, a mixed grid, interconnection and demand management.
• Improve security by diversifying sources, developing local supply, storing energy and cutting demand.

7.3 Solid waste in brief

Level of pollution management model	Waste examples
Altering human activity	Less packaging, repair, reuse, buying durable goods
Controlling release	Recycling, composting, energy-from-waste, deposit-return, landfill tax
Clean-up and restoration	Litter picks, reclaiming landfill sites, beach clean-ups

• Landfill releases methane (from organic waste breaking down without oxygen) and leachate (liquid that can pollute groundwater).
• Incineration cuts volume and can generate electricity, but produces air emissions and toxic ash.
• Composting diverts the organic fraction and cuts landfill methane.
• Recycling saves raw materials but depends on sorting, clean collection and a market.
• E-waste is both hazardous (toxic metals) and valuable (recoverable metals).

Must-know distinctions

• Natural capital vs natural income — the forest vs the yearly timber growth.
• Sustainable yield vs harvest — SY is growth; harvest is what you take.
• Renewable vs “no impact” — renewables still use land and materials.
• Energy efficiency vs energy conservation — technology vs behaviour.
• Energy security vs low-carbon — related goals that can conflict (domestic coal is secure but high-carbon).
• Percentage vs percentage points — a share rising from 18% to 31% is a rise of 13 percentage points.
• Reduce vs recycle — reduction prevents waste; recycling manages waste that already exists.

Quick self-test

1. Define natural income.
2. A grassland plot holds 2,600 kg of biomass. A year later, with no grazing, it holds 2,730 kg. Calculate the sustainable yield and express it as a percentage of the original stock.
3. Explain why harvesting at maximum sustainable yield is risky.
4. An aquifer holds 900 million m³. Recharge is 45 million m³ per year and abstraction is 60 million m³ per year. Estimate how long it will last if these rates continue.
5. State whether nuclear power is renewable, and why.
6. A country generates 180 TWh of electricity, 27 TWh of it from solar. Calculate the solar share.
7. Distinguish energy efficiency from energy conservation, with one example of each.
8. Give two reasons why a country that imports most of its gas has low energy security.
9. A city collects 20,000 t of SDW and recycles 6,000 t. Calculate the recycling rate.
10. A household produces 1.2 kg of waste a day. Calculate its waste per year.
11. Name the two main pollutants released from landfill sites.
12. Place these in waste-hierarchy order, best first: recycling, landfill, reduction, energy recovery, reuse.

Answers

1. The flow of goods or services produced by natural capital, such as timber growth or water filtration.
2. SY = 2,730 − 2,600 = 130 kg per year; 130 ÷ 2,600 × 100 = 5.0%.
3. Stock estimates are uncertain and a population held at half its carrying capacity has little margin, so a poor breeding year or an overestimate can push it into decline.
4. Net loss = 60 − 45 = 15 million m³ per year; 900 ÷ 15 = 60 years.
5. No. Uranium is a finite ore that forms far more slowly than it is mined.
6. 27 ÷ 180 × 100 = 15.0%.
7. Efficiency: same output from less energy (LED bulbs, insulation). Conservation: using less by choice (turning off lights, lower heating settings).
8. Supply can be cut by conflict or trade disputes; prices depend on world markets it cannot control.
9. 6,000 ÷ 20,000 × 100 = 30%.
10. 1.2 × 365 = 438 kg per year.
11. Methane (a greenhouse gas) and leachate.
12. Reduction → reuse → recycling → energy recovery → landfill.

Where marks are usually lost

• Calling the whole resource “natural income” when the question asks about the stock.
• Giving sustainable yield as the harvest total, or leaving out “per year”.
• Writing “renewables are clean” without naming a specific impact of a specific source.
• Classing nuclear power as renewable, or listing it as a fossil fuel.
• Quoting a percentage increase from a tiny base without saying the absolute amount.
• Confusing percentage change with percentage-point change in energy-mix data.
• Evaluating one waste method only for its advantages; “evaluate” needs strengths, limitations and a judgement.
• Mixing up the three levels of the pollution management model — composting is controlling release, not altering human activity.
• Forgetting units (TWh, m³, t per year) in calculated answers.
• Treating energy security and climate goals as the same thing, when the question wants the tension between them.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief, Environmental systems The brief lists subtopics for Topic 1 only; the subtopic numbering on this page follows the printable ESS checklist. and societies, first assessment 2026.

The brief gives Topic 7 Natural resources 10 teaching hours at SL and 18 at HL. It does not list the subtopics or learning outcomes for this topic, so the numbered subtopics and outcomes on this page follow the syllabus numbering used in the printable ESS checklist, not the brief itself.