ESS Systems and Models Explained

Systems and models form the foundation of IB ESS. Understanding how to apply systems thinking is essential for almost every topic in the course — and examiners test it frequently.

What is a system in ESS?

A system is a set of interconnected components that interact to form a complex whole. In ESS, environmental systems include:

• Inputs — energy, matter, or information entering the system
• Outputs — energy, matter, or information leaving the system
• Storages — where matter or energy is held within the system
• Flows / Transfers — movement of matter or energy between storages

Types of systems

• Open systems: Exchange both energy and matter with the surroundings (e.g., an ecosystem)
• Closed systems: Exchange energy but not matter (e.g., Earth as a whole)
• Isolated systems: Exchange neither energy nor matter (theoretical only)

Feedback loops

Feedback loops are a frequent exam topic. There are two types:

Test your understanding of systems and models with past paper questions — and get AI-powered feedback on your responses.

• Positive feedback: Amplifies change — moves the system further from equilibrium (e.g., melting ice reduces albedo, causing more warming)
• Negative feedback: Reduces change — returns the system towards equilibrium (e.g., increased CO₂ promotes plant growth, which absorbs more CO₂)

What are models?

Models are simplified representations of complex systems. In ESS, you will encounter:

• Systems diagrams: Show inputs, outputs, and flows
• Food webs: Model energy transfer in ecosystems
• Carbon cycle diagrams: Model global carbon flows

Models are useful for understanding and predicting environmental change, but they have limitations. Examiners often ask you to evaluate the strengths and weaknesses of models.

How to use systems thinking in exams

When answering ESS questions, think about:

• What are the inputs and outputs of this environmental process?
• Is there a feedback loop involved?
• How does changing one component affect the rest of the system?
• What are the limitations of our understanding of this system?

Learn more about the full IB ESS syllabus and study notes to see systems thinking applied across every topic.