Impact Assessment Fundamentals

The Life Cycle Impact Assessment (LCIA) phase transforms your inventory data into potential environmental impacts. While an inventory might list hundreds of different emissions and resource uses, LCIA distills this complexity into a manageable set of impact indicators that support decision-making.

From Inventory to Impacts

Consider a Life Cycle Inventory that shows your product emits 10 kg of CO₂, 0.5 kg of methane, and 0.02 kg of nitrous oxide. What does this mean for climate change? LCIA answers this question by translating these disparate emissions into a single Global Warming Potential score.

This translation process is the heart of impact assessment.

The Four Steps of LCIA

ISO 14044 defines LCIA as a sequence of mandatory and optional elements:

Mandatory Elements

1. Selection of Impact Categories, Indicators, and Models

Before you can assess impacts, you must decide which environmental issues matter for your study. Common impact categories include:

*Photochemical ozone formation reference substance varies by LCIA method: CML uses kg ethylene eq, ReCiPe uses kg NOx eq, EF/PEF uses kg NMVOC eq.

2. Classification

Classification assigns each inventory flow to the impact categories it affects. For example:

• CO₂ emissions → Climate change
• SO₂ emissions → Acidification, Human toxicity, Particulate matter formation
• Phosphate emissions → Eutrophication (freshwater)
• Crude oil extraction → Resource depletion (fossil)

Some flows affect multiple categories. SO₂, for instance, contributes to acidification, respiratory health effects, and particulate formation. These flows are classified to all relevant categories.

3. Characterization

Characterization calculates the magnitude of each flow's contribution to its assigned impact categories using characterization factors.

The characterization equation:

Impact Score = Σ (Inventory Amount × Characterization Factor)

Example: Calculating Global Warming Potential

Your inventory shows:

• 10 kg CO₂
• 0.5 kg CH₄ (methane)
• 0.02 kg N₂O (nitrous oxide)

Using IPCC AR6 characterization factors (100-year time horizon):

• CO₂: 1 kg CO₂ eq / kg
• CH₄: 29.8 kg CO₂ eq / kg (fossil sources)
• N₂O: 273 kg CO₂ eq / kg

GWP = (10 × 1) + (0.5 × 29.8) + (0.02 × 273)
    = 10 + 14.9 + 5.46
    = 30.4 kg CO₂ eq

Optional Elements

4. Normalization

Normalization puts your impact scores in context by comparing them to a reference value, typically the total annual impacts of a geographic region.

Normalized Score = Impact Score / Reference Value

If your product's GWP is 29.3 kg CO₂ eq, and the annual per-capita GWP for Europe is 8,100 kg CO₂ eq, the normalized score is:

29.3 / 8,100 = 0.0036 person-year equivalents

Normalization helps identify which impact categories are relatively significant, but doesn't indicate which categories are more important.

5. Weighting

Weighting assigns relative importance to different impact categories to enable aggregation into a single score. This step is value-based and controversial—different stakeholders may legitimately disagree on how to weight climate change versus biodiversity loss, for example.

Biogenic Carbon Accounting

When assessing products containing bio-based materials (wood, bio-plastics, agricultural products), the treatment of biogenic carbon is a critical methodological choice.

What Is Biogenic Carbon?

Biogenic carbon is CO₂ that was recently absorbed from the atmosphere by plants through photosynthesis, as opposed to fossil carbon that has been stored underground for millions of years. When bio-based products are combusted or decompose, this carbon returns to the atmosphere.

Accounting Approaches

The 0/0 approach (carbon neutral):

• Biogenic CO₂ uptake: not counted (0)
• Biogenic CO₂ release: not counted (0)
• Rationale: short-cycle carbon is "climate neutral" over the rotation period
• Used in: many traditional LCA studies, some EPD programs

The -1/+1 approach:

• Biogenic CO₂ uptake: counted as -1 kg CO₂ eq/kg CO₂
• Biogenic CO₂ release: counted as +1 kg CO₂ eq/kg CO₂
• Rationale: explicitly tracks carbon flows; important when timing matters
• Used in: PEF method, EN 15804:2012+A2:2019, GHG Protocol (reported separately)

When It Matters Most

Biogenic carbon accounting significantly affects results for:

• Wood and timber products (construction, furniture)
• Bio-based plastics and packaging
• Paper and pulp products
• Food and agricultural products
• Biofuels

For products with long service lives (e.g., wooden buildings), the -1/+1 approach shows temporary carbon storage benefits, while the 0/0 approach treats this as neutral.

Midpoint vs. Endpoint Approaches

LCIA methods differ in where they sit on the cause-effect chain:

Midpoint indicators (problem-oriented) measure impacts at an intermediate point:

• Global Warming Potential (kg CO₂ eq)
• Acidification Potential (kg SO₂ eq)
• Eutrophication Potential (kg PO₄ eq)

These have lower uncertainty but require interpretation about ultimate significance.

Endpoint indicators (damage-oriented) measure impacts at the point of damage:

• Human health (DALYs - Disability Adjusted Life Years)
• Ecosystem quality (species × years lost)
• Resource availability (future cost increase)

These are more intuitive but have higher uncertainty in the modeling chain.

Many modern LCIA methods like ReCiPe provide both midpoint and endpoint results.

Common LCIA Methods

Several established methodologies bundle characterization factors, normalization references, and (optionally) weighting sets:

ReCiPe

Developed by RIVM, Radboud University, CML, and PRé Sustainability, ReCiPe provides 18 midpoint categories that aggregate to 3 endpoint damage categories. It offers three cultural perspectives (Individualist, Hierarchist, Egalitarian) that reflect different assumptions about time horizons and manageability.

CML-IA

The CML method from Leiden University is a widely-used baseline approach focusing on midpoint categories. It's been influential in establishing standard LCIA practice and is well-documented in academic literature.

TRACI

The Tool for Reduction and Assessment of Chemicals and other environmental Impacts is the US EPA's recommended method. It uses characterization factors specific to US conditions and includes impact categories relevant to US regulatory frameworks.

EF Method (Environmental Footprint)

The European Commission's method for Product and Organization Environmental Footprints. It's required for EU PEF studies and is increasingly used for regulatory compliance in Europe.

Impact 2002+

A Swiss method that combines midpoint characterization with endpoint damage assessment, linking 14 midpoint categories to 4 damage categories.

Choosing an LCIA Method

Your method choice depends on several factors:

Interpreting LCIA Results

LCIA results require careful interpretation:

Hotspot Analysis

Identify which life cycle stages or processes contribute most to each impact category. A product might have raw material extraction dominating climate impacts but manufacturing dominating water use.

Trade-off Assessment

Compare performance across categories. A design change might reduce Global Warming Potential while increasing freshwater ecotoxicity. Decision-makers need to understand these trade-offs.

Uncertainty Awareness

All LCIA results carry uncertainty from:

• Inventory data variability
• Characterization factor uncertainty
• Model assumptions and choices

Responsible interpretation acknowledges this uncertainty rather than treating scores as precise values.

Limitations of LCIA

Be aware of what LCIA cannot do:

1. Not risk assessment: LCIA estimates potential impacts, not actual risks to specific populations or ecosystems

2. Spatial and temporal aggregation: Most methods don't differentiate where or when emissions occur

3. Incomplete coverage: Some environmental issues lack mature characterization models (biodiversity, microplastics, etc.)

4. Value judgments embedded: Choices in method development (time horizons, fate modeling, etc.) embed implicit values

Key Takeaways

1. LCIA translates inventory flows into environmental impact scores using characterization factors
2. The mandatory steps are selection, classification, and characterization; normalization and weighting are optional
3. Midpoint methods have lower uncertainty; endpoint methods are more intuitive
4. Choose LCIA methods based on geographic scope, regulatory context, and study goals
5. Results require careful interpretation considering trade-offs, hotspots, and uncertainty

Practice Exercise

You have a simplified inventory for a plastic bottle:

• 0.8 kg CO₂ from manufacturing
• 0.02 kg SO₂ from electricity generation
• 0.001 kg phosphate from wastewater
• 0.05 kg crude oil extracted

Using the characterization factors below, calculate the midpoint impact scores:

What additional factors would you need to fully characterize all flows?

What's Next?

With your impacts calculated, the final lesson in this track covers Interpretation and Reporting—how to draw valid conclusions from your results and communicate them effectively to your audience.

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Further Reading

• ISO 14044:2006 Section 4.4 (Life Cycle Impact Assessment)
• Hauschild, M.Z., & Huijbregts, M.A.J. (Eds.). (2015). Life Cycle Impact Assessment. Springer.
• European Commission. (2021). Environmental Footprint Method Guidance.