Precursor

An input that already carries embedded emissions of its own — the steel in a bolt, the clinker in cement.

A precursor is a produced input rather than a raw one. Its own footprint travels into whatever is made from it.

This is the point where a carbon figure stops being something you can measure on your own site. You can meter your furnace; you cannot meter your supplier’s. So the accuracy of a product footprint is usually limited by the quality of the precursor data behind it — which is a supplier-data problem before it is a calculation problem.

Under CBAM, purchased precursors must be accounted for in the embedded emissions of the finished good.

Embedded emissions The greenhouse gases released in producing a good, expressed per tonne of that good rather than per site or per year.
Scope 3 All other indirect emissions across the value chain — purchased goods, transport, use of sold products, end of life.
Primary data Data measured at its source — your meter, your supplier's actual production — as opposed to an industry average.