Example 1 — Feedback, and why the sign confuses people

Explain, using an example, how positive feedback can destabilise a system. [4]

Positive feedback amplifies a change, driving the system further from its original equilibrium rather than back toward it. ✓ For example, as Arctic sea ice melts, the reflective white surface is replaced by darker open ocean. ✓ The darker ocean has a lower albedo, so it absorbs more solar radiation and warms further instead of reflecting the energy away. ✓ This additional warming melts more ice, which exposes more ocean, and the cycle reinforces itself — so the system moves progressively further from equilibrium and may pass a tipping point beyond which the change is effectively irreversible. ✓

4/4.

The marks are in the loop closing. Many answers describe ice melting and stop. What makes it feedback is the final step returning to the start: more melting → more absorption → more melting. Say the loop out loud before writing it, and check it comes back to where it began.

Note the terminology carrying marks: amplifies, albedo, tipping point. In ESS the vocabulary is the assessment.

Example 2 — Distinguishing the equilibria

Distinguish between steady-state equilibrium and static equilibrium, giving an example of each. [4]

In a steady-state equilibrium there are continuous inputs and outputs, but the overall state of the system remains stable over time, whereas in a static equilibrium there are no inputs or outputs and nothing changes at all. ✓✓ An example of steady state is a mature forest: individual trees die and new ones grow, so matter and energy flow constantly, yet the total biomass and species composition stay roughly constant. ✓ An example of static equilibrium is a pile of rocks on a hillside, which simply remains as it is — a state rarely found in living systems. ✓

4/4.

The word "whereas" is doing real work again. And note the forest example explains why it is steady state rather than static — the flows continue. An example given without that explanation tends to score half.

Example 3 — An "evaluate" answer, and what the bands want

Evaluate the use of the ecological footprint as an indicator of sustainability. [7]

The ecological footprint estimates the area of land and water needed to supply a population's resources and absorb its waste, allowing it to be compared with the area actually available.

Strengths. It converts many different impacts into a single, comprehensible figure, which makes it powerful for communication and for comparison between countries — Qatar's footprint per capita is roughly an order of magnitude greater than India's, and that comparison is immediately intelligible to non-specialists. It makes ecological deficit visible: where the footprint exceeds available biocapacity, a population is drawing down natural capital rather than living on natural income. It can be tracked over time, so the effect of a policy can be assessed.

Limitations. It is a model, and aggregation is exactly where models lose information: very different impacts — carbon emissions, cropland, fisheries — are converted into a single area figure using assumptions that are themselves contested. It weights carbon heavily, so a country's footprint is sensitive to how its electricity is generated and can change sharply without any change in consumption. It says nothing about biodiversity loss, pollution or freshwater quality, so a country could reduce its footprint while degrading its environment in ways the indicator cannot see. Data quality varies considerably between countries.

Judgement. The ecological footprint is valuable as a communication and comparison tool, and its central message — that humanity's demand exceeds the planet's regenerative capacity — is robust. It is not reliable as a precise measure of sustainability, and should be used alongside indicators of biodiversity and pollution rather than in place of them.

Why this reaches the top band. Both sides are developed rather than listed. There are specific, named details rather than generic claims. It uses course terminology precisely — natural capital, natural income, ecological deficit, model. And crucially it ends with a judgement that is genuinely a judgement: not "there are advantages and disadvantages", but a statement about what the indicator is and is not good for.

The most common failure on this question is a strong one-sided answer. An essay listing only limitations, however well informed, cannot reach the top band, because evaluate requires both.

Example 4 — Applying value systems

Two people examine the same evidence about a proposed hydroelectric dam and reach opposite conclusions. Explain how this is possible. [4]

The two people hold different environmental value systems, which act as a lens determining how they perceive and weigh the same information. ✓ A technocentric observer would emphasise that the dam provides low-carbon electricity and that engineering can mitigate the ecological damage, concluding the benefits outweigh the costs. ✓ An ecocentric observer would emphasise the intrinsic value of the river ecosystem and the species displaced, holding that the loss is not compensated by the energy produced, and would prefer reduced consumption to new generation. ✓ Because their value systems assign different worth to the same outcomes, they reach different conclusions without either misreading the evidence — the disagreement is about values, not about facts. ✓

4/4.

The final sentence is what separates a 3 from a 4. The question is not really about dams; it is about why environmental disputes persist even when the science is agreed. Saying that explicitly shows you have understood what an EVS is for.

Educerie · original worked examples written against the published IB syllabus structure for Environmental Systems and Societies Topic 1, first assessment 2026. All scenarios are our own. Last reviewed 5 September 2026.