Product Carbon Footprint

A crucial first step in calculating a Product Carbon Footprint (PCF) is defining the system boundaries. These boundaries determine which processes and inputs/outputs should be included in the calculation and which can be neglected. Depending on the objective, a partial PCF (cradle-to-gate) may be sufficient. The system boundary should be plausible and transparent, as it greatly affects the PCF’s reliability and comparability. Due to the complexity of a PCF calculation, the system boundary often needs to be adjusted during the accounting process.

There are two main approaches for calculating a Product Carbon Footprint:

The system boundary defines the technological (which methods/technologies are included), spatial, and temporal scope covered by the accounting.

• The geographical boundary is especially relevant because energy mixes vary significantly between countries.
• The temporal boundary refers to the duration of the product lifecycle, from raw material extraction to disposal (cradle-to-grave), or up to product completion (cradle-to-gate).

The system boundary defines the technological (which methods/technologies are included), spatial, and temporal scope covered by the accounting.

• Cradle-to-gate: From raw material extraction to product completion
• Gate-to-gate: Only specific manufacturing or process stages
• Cradle-to-grave: From raw material extraction to product disposal/recycling

To calculate the Product Carbon Footprint, all material inputs, activities, and processes that are significant within the product lifecycle must be identified. Energy consumption is usually the largest source of GHG emissions.

The accounting result should include, within the system boundaries, all GHG emissions and removals from biogenic and non-biogenic (fossil) sources, including land-use changes.

According to the GHG Product Standard, all greenhouse gases listed in the Kyoto Protocol must be included: Carbon dioxide (CO₂), Methane (CH₄), Nitrous oxide (N₂0), Sulfur hexafluoride (SF₆), Partially halogenated fluorocarbons und Perfluorocarbons (PFCs).

GHG emissions are expressed in CO₂-equivalents (CO₂-eq), a universal unit for Global Warming Potential (GWP). For example, one unit of methane has 25 times the climate impact of CO₂, corresponding to 25 units of CO₂-eq.

Reducing complexity

Calculating a Product Carbon Footprint can be complex due to the many actors, processes, and locations involved across a product lifecycle.

The effort required depends on:

• Product complexity
• Quantity and origin of raw, auxiliary, and operating materials or intermediate products
• Number of actors and sites along the product lifecycle
• Co-products
• Waste and disposal
• Operational data collection (energy, auxiliary and operating materials)

To simplify the calculation, only significant processes are included in the product system. Minor processes can be excluded (outside the system boundary). A common exclusion criterion is that processes contributing less than 1% of total GHG emissions may be omitted.

Allocation

Co-products often occur when additional (by-)products are produced during the manufacturing of a main product. The energy and material flows, and consequently the associated greenhouse gas (GHG) emissions, must then be allocated proportionally among all products. Allocation is also common in transportation and recycling.

A clear allocation method with defined criteria should be established for the accounting. A frequently used approach is physical allocation, where inputs and outputs are assigned to the main product and co-products based on mass fractions or energy content. According to the GHG Product Standard, allocation should be conducted conservatively, assuming higher emissions for the main product when in doubt.

Data collection

Data collection is usually the most time-consuming part of a PCF calculation, as multiple countries and facilities are often involved. Therefore, transparency is essential. Data should be collected in a consistent format so that it can be converted to the reference unit (usually GHG emissions in kg CO₂-eq).

Before collecting primary data, a preliminary estimate or materiality analysis (potentially using secondary data) should be conducted to determine which processes are most relevant. For processes contributing a large share of emissions, high-quality data collection is essential. Supplier data can often be collected using questionnaires.

During data collection, both primary and secondary data are gathered (also called a material balance).

Primary data

Primary data consists of activity data or, often, direct emission data. These are collected for a specific process in the product system, typically covering quantities of energy carriers, intermediate products, raw, auxiliary, and operating materials.

According to the GHG Product Standard, companies must collect primary data for all processes under their control or ownership. For processes outside the company’s control or where no direct emission or activity data are available, secondary data can be used.

Secondary data

Secondary data comes from life cycle databases or input-output data, providing statistical GHG intensities (kg CO₂-eq per monetary or physical unit) for various production processes or sectors. Recognized secondary data sources include ecoinvent (paid) and ProBas (free). Upstream and downstream processes usually rely on secondary data.

Other useful data sources include invoices or enterprise resource planning (ERP) systems for raw and auxiliary material consumption and waste quantities.

If neither primary nor secondary data are available, data gaps occur. These should be minimized to reduce calculation uncertainty. Any gaps can be filled with estimated or proxy data from similar processes.