How circularity influences material stocks

Raising circularity ambition changes not only the quantity of material stock but also its composition and longevity. The trends of in-use stocks differ between mature and emerging material systems, revealing what the circularity levers are actually doing across materials.

Mean residence time—the average length of time a material stays in service—increases with circularity ambition across all decarbonisation pathways for each material except silicon. However, the same absolute increase carries very different implications depending on the starting point. For copper, the time the material is in use increases by roughly four to five years compared to the baseline mean lifetime of several decades (up to 40 years in the wire and cable material stream in 2020); for nickel, this is two to four years. Lithium gains a similar three to four years of material lifetime, but against a baseline of only around nine years. The proportional extension is therefore much larger for lithium, reaching 37% lifetime extension under a low decarbonisation pathway and 45% lifetime extension under high decarbonisation. Second-life stock,¹⁸² where material returns to service through reuse or remanufacturing, appears only under high circularity ambition across all decarbonisation scenarios, reaching around 13% of in-use stock for lithium and 16% of cobalt stock. Silicon, by contrast, accumulates no second-life stock under any configuration. The figure below shows how different decarbonisation scenarios alter both the size and composition of in-use stocks.

Overall stock patterns differ per material, with distinct circularity impacts. For copper and nickel, high circularity ambition can reduce the total amount of material accumulated in stocks while maintaining equivalent service: circularity primarily translates into reduced resource intensity. For lithium and cobalt, under high decarbonisation scenarios, high circularity ambition can instead increase total stock accumulated, because relieving the supply constraint allows material to reach applications that would otherwise have gone unserved (refer to the Two second-order effects section). Here, circularity shows up as increased material availability rather than reduced resource demand.

These contrasting outcomes reflect the different stages of stock development, measured by how much material is already in use relative to annual demand.

• In mature systems such as copper and nickel, existing in-use stock is equivalent to around 15 to 18 years of annual demand. Circularity therefore acts primarily on that accumulated stock, reducing the refined material required to meet demand as it grows.
• In emerging systems such as lithium and cobalt, in-use stock is equivalent to only two to four years of demand. There is little accumulated material to draw on, so circularity works instead by easing constraints and enabling more of the rapidly growing demand to be met.

The result is that higher circularity does not necessarily mean a smaller material stock; its effect depends on whether the system is primarily managing an established stock or building one.