What is a carbon footprint? Product, organisation and personal

A carbon footprint is the total greenhouse gas emissions caused by an activity or object, expressed in carbon dioxide equivalent. The definition is simple; the problem is that the same term is used at three different scales and they get mixed up.

Product carbon footprint

The emissions caused by one unit of product across its life cycle. The unit is per product: kg CO₂e per tonne of cement, kg CO₂e per m² of tile. The method is defined by ISO 14067, which inherits most of its rules from ISO 14044 — that is, from LCA.

A product carbon footprint is in fact a single-impact-category LCA. Functional unit, system boundary, allocation and cut-off rules demand the same discipline; only the result table shrinks to one row.

Corporate carbon footprint

The total emissions a company causes over a calendar year, in tonnes CO₂e per year. The GHG Protocol splits it into three scopes: direct emissions (Scope 1), purchased energy (Scope 2) and everything in the value chain (Scope 3). ISO 14064-1 does the same job with six categories.

In manufacturing, 70 to 90 per cent of the total sits in Scope 3 — the real magnitude is not in the company’s own stack but in its supply chain and in how its products are used.

How the two connect

The connection runs both ways, and most confusion starts here. Your suppliers’ product footprints feed your Scope 3 Category 1. Your product’s footprint enters your customer’s Scope 3. The same emission is counted under different names at different links in the chain — that is not double counting but different accounting boundaries.

Conversion is possible too: multiply the per-product footprint by annual production or sales volume and you reach the corporate magnitude. For that to hold, though, the product footprint must reflect your actual production route; a sector average makes the multiplication meaningless.

Personal carbon footprint

The emissions from an individual’s annual consumption — the most widely known usage in public discourse. It is methodologically the loosest, because consumption data rests on estimates. It is not held to the same rigour as corporate and product accounting and should not be confused with either.

Three common mistakes

• Comparing numbers from different system boundaries — a cradle-to-gate value cannot be set against a cradle-to-grave one
• Dividing a corporate total by unit count and calling it a product footprint — overheads and product mix break that
• Looking only at carbon and ignoring other impacts — a low-carbon option can be worse on water or toxicity