What is Attributional LCA?

Attributional LCA quantifies the environmental impacts physically attributed to a product. It asks: what emissions and resource consumption does this product system require?

This approach dominates LCA practice. Environmental Product Declarations, carbon footprints, and most product assessments use attributional methods. The methodology tracks physical flows through supply chains and allocates shared burdens based on product relationships.

The Accounting Perspective#

Think of attributional LCA as environmental accounting. Just as financial accounting tracks costs associated with a product, attributional LCA tracks environmental burdens. Each product carries its share of system impacts.

A factory producing multiple products needs to split emissions across outputs. Attributional LCA allocates based on physical relationships (mass, energy) or economic value. Each product receives its proportional share.

Static System Description#

Attributional LCA describes the system as it currently exists. Background data represents average conditions. The electricity grid has a certain carbon intensity. Steel production has a certain emission factor. These values characterise the existing system.

The approach doesn’t predict how systems respond to changes. If you reduce demand for a product, attributional LCA doesn’t model resulting market adjustments. It simply calculates the impacts associated with current production patterns.

When to Use Attributional LCA#

Attributional LCA suits several situations:

Comparative assessment of similar products works well. You want to know whether recycled plastic packaging has lower impacts than virgin plastic packaging. Both products exist in the current system. Attributional methods quantify their respective burdens.

Environmental reporting uses attributional approaches. Companies calculate their product carbon footprints using emission factors for purchased electricity, materials, and transport. This accounting determines their environmental footprint.

Product declarations follow attributional conventions. EPDs report impacts attributed to declared products. Builders can add up EPD impacts across building components because each product carries its share of system burdens.

Benchmarking requires consistent accounting. Comparing products from different manufacturers needs standardised methods. Attributional approaches with defined allocation rules enable this consistency.

Allocation Decisions#

Multifunctional processes create allocation challenges. Refineries produce multiple fuels. Paper mills generate electricity alongside pulp. Agricultural systems yield multiple crops.

Attributional LCA allocates impacts across co-products. Mass allocation splits by weight. Energy allocation uses calorific values. Economic allocation reflects market prices. Each method creates different results.

ISO 14044 establishes an allocation hierarchy. First avoid allocation through subdivision or system expansion. If unavoidable, allocate based on physical relationships. Economic allocation is acceptable when physical relationships don’t apply.

These allocation rules aim for consistency rather than representing causal relationships. A by-product receives its allocated share regardless of whether it drives the process.

Supply Chain Representation#

Attributional LCA uses process-based models. Each supply chain stage gets represented by its inputs and outputs. Background databases provide data for common materials and processes.

Generic data represents typical conditions. European electricity mix data aggregates across countries. Steel production data averages across production routes. This builds representative models of supply chains.

Site-specific data improves accuracy for foreground processes. Your manufacturing facility has measured emissions. Transport distances come from actual logistics. These primary data replace generic values where available.

Limitations#

Attributional LCA can’t predict consequences of decisions. If you eliminate a product, the approach doesn’t model how markets adjust. Surplus production capacity might absorb demand changes with minimal emission reduction.

By-product allocation creates arbitrary divisions. Milk and beef both come from cattle, but allocation rules determine their respective impact shares. These splits don’t reflect causation – both products jointly drive cattle production.

Average data may not represent marginal supply. If increased demand is met by specific suppliers rather than average market conditions, attributional results misrepresent actual impacts.

Comparison with Consequential LCA#

Consequential LCA asks different questions. Rather than “what impacts are attributed to this product”, it asks “what happens if we change the system”. These approaches use different methods and produce different results.

Attributional suits descriptive questions. Consequential suits change-oriented questions. Neither is universally correct. The choice depends on your decision context.

Most regulations and standards specify attributional approaches. EPDs, carbon accounting protocols, and product comparisons use these methods. They provide consistency even if they don’t model system dynamics.

Practical Implementation#

Attributional LCA requires:

• Process flow diagrams showing all activities
• Input and output data for each process
• Allocation rules for multifunctional processes
• Background data for materials and energy
• Impact assessment methods

Software tools like openLCA implement attributional methods. You build process models, connect them through product flows, and calculate impacts using established allocation procedures.

The methodology produces repeatable results. Different practitioners following the same rules should reach similar conclusions. This consistency enables comparison and verification.