How to calculate a carbon footprint

Cornerstones of the calculations

Taking a scientific approach and ensuring transparency requires a multi-stage process and independent verification. The EN ISO 14067 standard [3] specifies the requirements and guidelines for quantification of carbon footprints for products. The core element of this standard is the carbon footprint study. [3]Key steps include defining system boundaries along with the pertinent process steps and information on data recording, data sources and data quality. Any uncertainties in the data must also be disclosed. Greenhouse gas emissions are calculated on the basis of established standards, such as the GHG Protocol, and contain all material influencing factors. If data is unavailable or lacks sufficient resolution, including elsewhere in the supply chain, this can make the calculation a challenging proposition. [1, 2, 3, 4]

AMAG AL4® ever primary aluminium

A carbon footprint includes emissions from resource extraction and raw materials procurement as well as production at the smelting location. Based on the cradle-to-gate approach and in line with the PCR [5], downstream processes such as sales, use and disposal are not considered.

The carbon footprint of an aluminium smelter is influenced to a significant extent by its energy source. The Alouette smelter in Canada is able to rely entirely on hydroelectric power, which means that the energy-related CO₂ emissions are negligible. In contrast, where smelters are powered by coal-fired power stations, the GHG emissions from the purchased electricity are eight times higher than for electricity from renewable sources, while electricity from gas-fired power stations has four times the GHG emissions. [6] High-efficiency machinery and continuous optimizations also keep CO₂ emissions low at the Alouette smelter. The Scope 3 emissions of primary aluminium mainly occur in the upstream value chain, in the production of primary materials such as alumina. In addition to the electricity mix used to power manufacturing processes, it is clear that the manufacturing processes themselves and material origins significantly impact the carbon footprint of primary aluminium. The emissions of primary aluminium with an AMAG AL4® ever certificate are no more than 4.0 tons of CO₂ per ton of aluminium. This represents a more than 70% reduction in greenhouse gas emissions when compared to the global average of 15.1 tons of CO₂ per ton of aluminium. [7]

Cast and rolled products

In a CFP study, the definitions of system boundaries and carbon footprint calculations for cast and rolled products at AMAG’s Ranshofen site are documented in the same way as primary aluminium and meet the requirements of EN ISO 14067. The calculations for cast and rolled products comprise the Scope 1 and Scope 2 emissions generated at AMAG’s Ranshofen site as well as upstream Scope 3 emissions using the cradle-to-gate approach (Figure 1).  AMAG’s Sustainability Strategy relies on recycling aluminium.Despite the high average scrap utilization rate across all products, each alloy has different requirements for primary aluminium, external rolling slabs and alloying materials. Although they occur upstream in the value chain and are not generated at the Ranshofen site, the Scope 3 emissions associated with these raw materials are a significant factor in the overall carbon footprint of these products.

Thanks to the use of green electricity from hydroelectric power plants and other renewable sources, the Ranshofen site has generated zero Scope 2 emissions since the 2018 reporting year. The calculation of relevant Scope 1 emissions for the product-specific carbon footprint considers the process route for on-site manufacturing, including sorting, separation and re-smelting processes for internal scrap and dross. In addition, all other Scope 1 emissions - such as internal transport activities, diesel fuel for company vehicles and the heating of office buildings - are allocated to products aliquot as an AMAG overhead. The output of production steps describes the actual output from input materials broken down by the plant and machinery involved, which makes it possible to attribute all generated greenhouse gas emissions to the resulting final product. The calculation method employed by AMAG follows the cut-off principle to ensure that environmental impacts are duly considered, with emissions allocated to the process in which they occur. This takes account of material savings and the high value of recycling while also promoting recycling-friendly product design.

Consequently, the carbon footprint of cast and rolled products is influenced to a significant extent by the composition of their raw materials (primary metal vs. secondary metal/scrap), the output of key process steps, the plant and machinery involved and their energy source(s).

AMAG AL4® ever product family

AMAG AL4® ever variants for aluminium rolled and cast products feature a particularly small carbon footprint, making them an ideal choice for customers seeking to achieve their own environmental targets. A basic requirement for these products is a positive, completed feasibility study, including calculation of the carbon footprint based on the customer’s specific requirements and taking into account the order volume, the technical specifications and the required raw materials (primary aluminium/rolling slabs, scrap and alloy metals). Each product’s carbon footprint is confirmed in a test certificate. AMAG TITANAL® AL4® ever is a prime example: while its mechanical parameters remain unchanged from the standard AMAG TITANAL® variant, this particularly resource-efficient variant is available with a smaller carbon footprint as part of the AMAG AL4® ever family.