IB Environmental Systems and Societies (ESS) is one of the most distinctive courses in the Diploma Programme. It combines environmental science with the study of how human societies use, value and manage the natural world, and it asks you to apply both to real problems such as climate change, biodiversity loss and pollution.
A new ESS course started with first assessment in 2026. The biggest change is that ESS is now offered at Higher Level (HL) as well as Standard Level (SL). This guide explains how the new course works, from its key concepts and topics to the exams and the individual investigation. All the facts come from the IB's Environmental systems and societies guide (first assessment 2026, updated November 2025), written in our own words.
Key Takeaways
- ESS is an interdisciplinary course that counts as an individuals and societies (group 3) subject, a sciences (group 4) subject, or both.
- From 2026 it is offered at SL (150 hours) and HL (240 hours). HL adds more content and three HL lenses: environmental law, economics and ethics.
- The whole course is built on three key concepts: perspectives, systems and sustainability.
- SL is assessed by Paper 1 (25%), Paper 2 (50%) and the internal assessment (25%). HL is assessed by Paper 1 (30%), Paper 2 (50%) and the internal assessment (20%).
- The internal assessment is an individual investigation of up to 3,000 words, marked out of 30 against six criteria.
What Is IB ESS?
ESS looks at 21st-century environmental challenges through two lenses at once: the science of how natural systems work, and the social, economic, cultural, political and ethical choices societies make about them. It draws on ecology, chemistry, geography, economics, psychology, law, philosophy and more.
Because ESS is interdisciplinary, you can count it as your group 3 subject, your group 4 subject, or both. If you count it as both, you can take an extra subject from any other group.
No prior study of ESS or any particular science is required. The IB lists being open-minded, inquiring, a good thinker and a good communicator as the qualities that help most.
The IB's Aims for ESS
The course aims to help you:
1. Understand your own environmental impact, and humanity's impact on the Earth 2. Understand a wide range of perspectives on sustainability issues 3. Use critical thinking to evaluate the tensions around environmental issues 4. Use a systems approach to see environmental issues as a whole 5. Feel inspired to engage with environmental issues, locally and globally
What Has Changed in the 2026 Course?
If you have looked at older ESS resources, here is what is different:
| Previous course (assessed up to 2025) | New course (first assessment 2026) | |
|---|---|---|
| Levels | SL only | SL and HL |
| Teaching hours | 150 | 150 at SL, 240 at HL |
| Course structure | Eight topics, starting with "Foundations of ESS" | A foundation topic built on three key concepts (perspectives, systems, sustainability), then seven further topics |
| HL extension | None | Extra HL content in every topic, plus three HL lenses: environmental law, economics and ethics |
| Internal assessment | Individual investigation, up to 2,250 words | Individual investigation, up to 3,000 words, marked against six new criteria (including a new "strategy" criterion) |
The new guide also gives much more space to ideas such as planetary boundaries, doughnut economics, the circular economy, environmental justice, rewilding and urban systems. It includes the collaborative sciences project, and allows students to develop IA methods together in small groups.
The Three Key Concepts
Topic 1 (Foundation) introduces three key concepts, and the IB recommends teaching it first. They come up again in every later topic.
| Key concept | What it means in ESS |
|---|---|
| Perspectives | How a person's values, worldview and lived experience shape how they see environmental issues and what they decide to do. You study models such as environmental value systems, and the range from technocentric to anthropocentric to ecocentric viewpoints. |
| Systems | Seeing the environment as interacting parts with stores, flows, inputs and outputs. You use system diagrams and models, and study feedback loops, tipping points, equilibrium and resilience. |
| Sustainability | Using resources and managing systems so they stay viable for future generations, across environmental, social and economic "pillars". You meet environmental justice, ecological footprints, the UN Sustainable Development Goals, planetary boundaries, doughnut economics and the circular economy. |
Course Content: The Eight Topics
| Topic | Subtopics | SL hours | HL hours |
|---|---|---|---|
| 1: Foundation | Perspectives Systems Sustainability | 16 | 16 |
| 2: Ecology | Individuals, populations, communities and ecosystems Energy and biomass in ecosystems Biogeochemical cycles Climate and biomes Zonation, succession and change in ecosystems | 22 | 35 |
| 3: Biodiversity and conservation | Biodiversity and evolution Human impact on biodiversity Conservation and regeneration | 13 | 26 |
| 4: Water | Water systems Water access, use and security Aquatic food production systems Water pollution | 12 | 25 |
| 5: Land | Soil Agriculture and food | 8 | 15 |
| 6: Atmosphere and climate change | Introduction to the atmosphere Climate change: causes and impacts Climate change: mitigation and adaptation Stratospheric ozone | 10 | 23 |
| 7: Natural resources | Natural resources: uses and management Energy sources: uses and management Solid waste | 10 | 18 |
| 8: Human populations and urban systems | Human populations Urban systems and urban planning Urban air pollution | 9 | 15 |
| Other teaching time | |||
| HL lenses (HL only) | Environmental law Environmental economics Environmental ethics | – | 17 |
| Experimental programme | Practical work (30 hours) Collaborative sciences project (10 hours) Individual investigation (10 hours) | 50 | 50 |
| Total | 150 | 240 | |
What You Study in Each Topic
- Topic 2, Ecology. How ecosystems work: species and populations, carrying capacity, energy flow and food webs, the carbon and nitrogen cycles, biomes and the tricellular model of atmospheric circulation, and how communities change through zonation and succession. You also learn field methods such as quadrats, transects and the Lincoln index. HL adds topics such as fundamental and realized niches, r- and K-strategists, primary and secondary productivity, ENSO, and why the idea of a climax community is debated.
- Topic 3, Biodiversity and conservation. How biodiversity arises through evolution and natural selection, how to measure it with Simpson's reciprocal index, the human threats to it, the IUCN Red List, and how habitats are conserved and restored, including rewilding. HL adds speciation, mass extinctions, the Anthropocene, key biodiversity areas and how to judge whether conservation projects succeed.
- Topic 4, Water. The hydrological cycle, water security and scarcity, fisheries and aquaculture (including maximum sustainable yield), and water pollution and eutrophication. HL adds ocean stratification, thermohaline circulation, water stress, transboundary disputes, sewage treatment and biotic indices.
- Topic 5, Land. Soil as a system, and how food is produced: agricultural systems, the Green Revolution, soil conservation, diet and food security. HL adds soil profiles and horizons, regenerative farming, permaculture, vertical farming and food distribution.
- Topic 6, Atmosphere and climate change. The greenhouse effect, the causes and impacts of climate change, mitigation and adaptation strategies, and the ozone layer and the Montreal Protocol. HL adds Milankovitch cycles, climate models and hindcasting, tipping cascades, geoengineering and climate justice.
- Topic 7, Natural resources. Natural capital and ecosystem services, renewable and non-renewable energy, and solid waste management. HL adds environmental impact assessments, resource security, nuclear power and the environmental costs of battery storage.
- Topic 8, Human populations and urban systems. Population dynamics, age–sex pyramids and the demographic transition model, urbanization and urban planning, and urban air pollution and acid rain. HL adds dependency ratios, environmental migration, ecological urban planning, green architecture and photochemical smog.
The HL Lenses
HL students study three extra "lenses" (17 hours in total) and apply them across the whole course:
| HL lens | Hours | What it covers |
|---|---|---|
| Environmental law | 5 | How laws at local, national and international levels govern resource use and pollution, international conventions and protocols, environmental constitutionalism, and legal personhood for natural entities such as rivers |
| Environmental economics | 7 | Market failure, the polluter-pays principle, greenwashing, the tragedy of the commons, valuing ecosystem services, ecological economics, decoupling and degrowth, and the circular and doughnut economy models |
| Environmental ethics | 5 | Instrumental and intrinsic value, moral standing, virtue, consequentialist and rights-based ethics, the "appeal to nature" fallacy, and links with social justice movements |
What Is the Difference Between SL and HL?
Both levels share the same key concepts, the same foundation topic, the same internal assessment and the collaborative sciences project. At HL:
- There is more content. Every topic has HL-only material, which gives you both more breadth and more depth.
- The HL lenses of law, economics and ethics are studied and applied to environmental issues across the course.
- More connections are needed. The IB describes some HL content as conceptually more demanding, and expects HL students to link more areas of the syllabus and to evaluate critically.
- The exams are longer. Paper 1 is two hours instead of one, and Paper 2 requires two essays instead of one.
Skills You Develop
The IB groups ESS skills into four tools and a three-stage inquiry process:
| Tools | Inquiry process |
|---|---|
| Experimental techniques: lab work, fieldwork (quadrats, transects, capture–mark–release–recapture, abiotic measurements), surveys and secondary data | Exploring and designing: a focused research question, a testable hypothesis, variables and a risk assessment |
| Technology: data loggers, spreadsheets, databases, GIS and footprint calculators | Collecting and processing data: tables, graphs, measures of spread and statistical tests |
| Mathematics: calculations, graphs, indices (such as Simpson's reciprocal index and the Lincoln index), statistical tests (such as Spearman's rank, t-tests and chi-squared) | Concluding and evaluating: valid conclusions, uncertainty, weaknesses and realistic improvements |
| Systems and models: constructing and interpreting system diagrams and models |
Assessment Overview
Standard Level (SL)
| Component | What it involves | Time | Weighting |
|---|---|---|---|
| Paper 1 (35 marks) | Questions analysing and evaluating data from a previously unseen case study All questions compulsory | 1 hour | 25% |
| Paper 2 (60 marks) | Section A: short-answer and data-based questions (40 marks) Section B: one structured essay from a choice of two (20 marks) | 2 hours | 50% |
| Internal assessment (30 marks) | Individual investigation, up to 3,000 words | 10 hours | 25% |
Higher Level (HL)
| Component | What it involves | Time | Weighting |
|---|---|---|---|
| Paper 1 (70 marks) | Questions analysing and evaluating data from a previously unseen case study All questions compulsory | 2 hours | 30% |
| Paper 2 (80 marks) | Section A: short-answer and data-based questions (40 marks) Section B: two structured essays from a choice of three (40 marks) | 2 hours 30 minutes | 50% |
| Internal assessment (30 marks) | Individual investigation, up to 3,000 words (same task as SL) | 10 hours | 20% |
Paper 1: The Case Study
Paper 1 gives you a range of data, such as maps, graphs, tables, photos and text, about a case study you haven't seen before. Every question is based on analysing and evaluating that material, so this paper rewards strong data-handling skills and the ability to apply course concepts to an unfamiliar place.
Paper 2: Short Answers and Essays
Section A tests your knowledge and understanding across the course through short-answer and data-based questions. Section B essays are worth 20 marks each. The final part of each essay (9 marks) is marked holistically using markbands. These reward accurate ESS terminology, well-explained real-world examples, balanced analysis and well-supported conclusions. At HL, the markbands also look for HL lens content.
A calculator is required for both papers, and graphic display calculators are allowed.
Internal Assessment: The Individual Investigation
The internal assessment is the same at SL and HL. You design and carry out your own investigation into an environmental research question, then write it up as a report. The IA:
- is written up as a report of no more than 3,000 words
- takes about 10 hours of class time
- is marked by your teacher and moderated by the IB
- can use primary or secondary data, and quantitative or qualitative data: lab experiments, fieldwork, surveys or databases
- begins with the title, your personal code, any group members' codes and the word count. No cover page or contents page is needed.
Charts, diagrams, data tables, equations and calculations, citations, the bibliography and headers do not count towards the 3,000 words.
The Six IA Criteria
| Criterion | What it looks at | Marks |
|---|---|---|
| A: Research question and inquiry | Explaining a local or global environmental issue with enough background research, and stating a focused research question | 4 |
| B: Strategy | Describing an existing or developing strategy that addresses an environmental issue linked to your question, and explaining a tension between different perspectives that it creates | 4 |
| C: Method | A repeatable method that collects enough relevant data to answer the question | 4 |
| D: Treatment of data | Communicating and processing raw data clearly and correctly so the findings address the question | 6 |
| E: Analysis and conclusion | Explaining patterns and trends, including bias, reliability, validity and uncertainty, and reaching a supported conclusion | 6 |
| F: Evaluation | Evaluating specific weaknesses and limitations, realistic improvements and unresolved questions | 6 |
| Total | 30 |
Things to Know About the IA
- The strategy criterion is new. You need to discuss a real or developing strategy for an environmental issue linked to your question, and a tension it causes between economic, social, cultural, political or environmental perspectives. The strategy can differ from the one you investigate, as long as the connection is clear.
- Group work is allowed, within limits. Up to three students can develop a method together, but each student needs their own research question, their own data (for example a different variable) and their own individually written report.
- A literature review on its own doesn't count as a method. Your method must let someone else repeat your investigation.
- Database investigations are fine. If you use a class or external database, your method should explain how you filtered and sampled the data.
- It can't overlap with your EE. Your Extended Essay can't be based on your ESS IA research question.
For expert help planning your investigation, see our internal assessment support.
The Collaborative Sciences Project
ESS students also take part in the collaborative sciences project (10 hours). This is an interdisciplinary project with students from other science subjects that tackles a real-world problem. It builds teamwork, negotiation and leadership skills. It is a course requirement but isn't graded.
ESS and the Extended Essay
You can write your Extended Essay in ESS, but only on the subject-focused pathway. ESS can't be combined with another subject in an interdisciplinary EE. A good ESS essay must link a natural environmental system with human society, and is expected to use a systems approach. See our guide to the 2027 Extended Essay for the full rules.
Command Terms
ESS exam questions use command terms that tell you how much depth to give. The IB groups them by assessment objective:
| Assessment objective | Example command terms |
|---|---|
| AO1: Knowledge and understanding | Define Draw Label List Measure State |
| AO2: Application and analysis | Annotate Apply Calculate Describe Distinguish Estimate Identify Interpret Outline |
| AO3 and AO4: Evaluation, synthesis and skills | Analyse Compare and contrast Construct Discuss Evaluate Examine Explain Justify Suggest To what extent |
For a full explanation, see our complete guide to IB command terms.
Tips for Success in IB ESS
1. Think in systems. Practise drawing system diagrams with stores, flows and feedback loops. They help in every topic and on both papers. 2. Build a bank of case studies. The guide asks for named, real-world examples in many places, for example an ecosystem collapse, a fishery, a rewilding project or an environmental injustice. Learn the specific details. 3. Always show more than one perspective. Strong answers explain how different stakeholders and worldviews see the same issue. 4. Practise data questions. Paper 1 is entirely data-based, so get comfortable with unfamiliar graphs, maps and tables. 5. Plan essays around the markbands. Use precise terminology, well-explained examples, balanced analysis and a clear judgement. 6. HL students: use the lenses. Bring law, economics and ethics into your essays wherever they are relevant. 7. Use past papers. Find out why past papers are the ultimate tool for exam preparation.
Common Mistakes to Avoid
- Describing environmental problems without evaluating solutions or perspectives
- Using vague examples ("a country in Africa") instead of named, specific cases
- Writing an IA without a clear strategy and tension discussion (Criterion B)
- Choosing an IA question that is too broad for 3,000 words
- Leaving out uncertainty, reliability and bias when concluding
Frequently Asked Questions
Is IB ESS now available at HL?
Yes. From first assessment in 2026, ESS is offered at both SL and HL. Previously it was SL only.
Does ESS count as a science or a humanities subject?
Both. You can count ESS as a group 3 (individuals and societies) subject, a group 4 (sciences) subject, or both at once. If you count it as both, you take an extra subject from another group.
Is ESS easier than Biology or Geography?
It is different rather than easier. ESS needs scientific understanding, data skills and well-argued essays that consider many perspectives. HL ESS in particular involves a lot of content and longer exams.
How long is the ESS internal assessment?
Up to 3,000 words. It is marked out of 30 and is worth 25% of the grade at SL and 20% at HL.
Do I need a science background for ESS?
No. The IB requires no prior learning, and all the skills you need are taught within the course.
What calculator do I need?
A calculator is required for both papers, and graphic display calculators are permitted.
Get Support With IB ESS
Whether you need help with ecology calculations, case studies, essay technique or your individual investigation, our experienced IB ESS tutors can help, online wherever you are. To understand how ESS fits into your diploma, read about how your IB score is calculated.
