Environmental Impact and Sustainability
This domain tests impact assessment process and life-cycle thinking together. You are expected to know how significance is decided, how boundaries are drawn, and how to convert a life-cycle inventory into a per-kilowatt-hour carbon intensity that can fairly be compared across technologies.
Core rules and concepts
- EIA sequence. Screening, scoping, baseline characterisation, impact prediction, significance evaluation, mitigation, monitoring, and consultation. Significance combines magnitude, duration, reversibility and receptor sensitivity; magnitude alone is never sufficient.
- Mitigation hierarchy. Avoid, then minimise, then restore, then offset. Offsets are the last resort and require additionality, permanence and no net loss.
- Cumulative and transboundary effects must be assessed against other past, present and reasonably foreseeable projects, not against the project in isolation.
- LCA standards. ISO 14040 and 14044 define goal and scope, inventory, impact assessment and interpretation. The functional unit, for example 1 kWh delivered to the grid, drives every comparison. System boundary choices (cradle-to-gate versus cradle-to-grave), allocation rules and whether the study is attributional or consequential determine the results.
- Impact categories. Global warming potential in gCO2e/kWh, acidification, eutrophication, water consumption, land use intensity and resource depletion. Indicative life-cycle carbon intensities: coal about 820-1,000, gas combined cycle about 450-500, solar PV about 40-50, wind about 11-12, nuclear about 12, hydro about 24 gCO2e/kWh.
Worked example
A 100 MW wind farm with a 35% capacity factor and 25-year life has 90,000 tCO2e embodied across manufacturing, transport, installation and decommissioning. Annual generation = 100 MW × 0.35 × 8,760 h = 306,660 MWh. Lifetime generation = 7.67 TWh. Carbon intensity = 90,000 t / 7,666,500 MWh ≈ 11.7 gCO2e/kWh, consistent with published wind figures. Against a gas combined cycle at 490 g/kWh, each TWh of wind avoids roughly 478,000 tCO2e; but for policy appraisal the correct comparator is the displaced marginal unit, not the fleet average.
Traps that cost marks
- Calling renewables zero-emission; manufacturing and decommissioning emissions exist.
- Comparing a cradle-to-gate figure for one technology with a combustion-only figure for another.
- Mixing CO2 with CO2e, or omitting non-CO2 gases.
- Judging significance from magnitude alone without receptor sensitivity.
- Ignoring water consumption and land use while focusing only on carbon.