CO2eq and the Sustainability of Steel

 

Introduction

Steel is a material used by humanity since antiquity. Its versatility has ensured that it continues to be present over time, evolving along with the advances of society. Today it is present in the most diverse industries, with thousands of engineering alloys developed for the most diverse applications. Currently, one of the challenges for the growth of the steel industry is sustainability: from the extraction of iron from nature, through its transport and the primary production of steel to its disposal and recycling. The analysis presented here adopts a cradle-to-gate scope, covering emissions from raw-material extraction through to the production of the finished metal.

CO2e Comparison

A relevant factor in this process is the release of gases during its production. Many of these gases increase the greenhouse effect and are also released by other industrial processes. The main gases responsible for the greenhouse effect (GHG – greenhouse gases) are CO₂ (carbon dioxide), CH₄ (methane), N₂O (nitrous oxide), and the CFCs (chlorofluorocarbons) [1]. ISO 14064 [2] uses CO₂e as a way to simplify the quantification of the impact of these gases: it compares how much each gas contributes to the greenhouse effect with the effect of CO₂.

Carbon dioxide is used as a reference because it is responsible for about 80% of the warming related to human production of greenhouse gases [3]. It is also the main gas related to human activity, mainly in energy production, in industrial activity, and in transportation. While other gases disperse after a few years, CO₂ remains in nature for centuries, accumulating its effect over time [4].

Therefore, when considering sustainability in the material selection process, CO₂e (also cited as CO₂eq or GWP) is one of the main factors. Below is Table 1 with the amount of CO₂ released in the production of the main metallic materials currently:

Table 1: CO₂e related to primary and secondary production of the main metallic alloys [5]

Metal	ton CO₂e/ton – primary	ton CO₂e/ton – secondary
Aluminum	15.1	0.52
Magnesium	43.4–55.4	0.2
Titanium	31–35.7	7.8
Nickel	4.8–139 ·       Class 1: 13; ·       FeNi: 45–51; ·       NiSO₄(H₂O)₆: 3.6–5.4	0.3–3.7 from scrap 2.1–7.8 from batteries
Copper	1.1–8.5	0.2–1.9
Steel	2.18	0.8–1.9

 

 

Discussion and Outlook

In all metals, a decrease in emissions is observed between production by the primary route and by the secondary route. In the case of steel, the primary emission is the lowest among the metals studied, remaining among the materials with the lowest CO₂e also in secondary production. Therefore, when using CO₂e as a criterion, it can be said that steel is a sustainable material. On the basis of CO₂e alone, steel is among the most sustainable structural metals. Future material-selection decisions should incorporate full LCA (ISO 14040/14044) and the additional indicators listed above:

·       ISO standards: 14040, 14044, 14021, 14025, 14067, 14046, 26000 (social responsibility);

·       other standards: EN 15804+A2 or PEF.

References

1.   U.S. Environmental Protection Agency. “Understanding Global Warming Potentials.” Accessed April 20, 2026. https://www.epa.gov/ghgemissions/understanding-global-warming-potentials.

2.   International Organization for Standardization. ISO 14064-1:2018. Greenhouse gases — Part 1: Specification with guidance at the organization level for quantification and reporting of greenhouse gas emissions and removals. 2nd ed. Geneva: ISO. 2018. https://www.iso.org/standard/66453.html.

3.   “Climate Change: Atmospheric Carbon Dioxide.” NOAA Climate.gov. 2024.  https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide.

4.   “Carbon Dioxide: Earth’s Hottest Topic Is Just Warming Up.” NOAA Climate.gov. 2025. https://www.climate.gov/news-features/understanding-climate/carbon-dioxide-earths-hottest-topic-just-warming.

5.   Sources for Table 1 (data on primary and secondary production CO₂e):

I.    Aluminum (primary and secondary): International Aluminium Institute. “As Well as Aluminium Recycling Saving 95% of the Energy Needed for Primary Aluminium Production the Recycling Process Saves a Similar Percentage in Greenhouse Gas Emissions.” Accessed April 21, 2026. https://international-aluminium.org/landing/as-well-as-aluminium-recycling-saving-95-of-the-energy-needed-for-primary-aluminium-production-the-recycling-process-saves-a-similar-percentage-in-greenhouse-gas-emissions/.

II.  Magnesium (primary): García Gutiérrez, Isabel, et al. 2020. “Influence of the Composition on the Environmental Impact of a Casting Magnesium Alloy.” Sustainability 12, no. 24 (2020): 10494. https://www.mdpi.com/2071-1050/12/24/10494.

III.Magnesium (secondary): Ehrenberger, Simone. Carbon Footprint of Magnesium Production and its Use in Transport Applications. 2020. https://www.researchgate.net/profile/Simone-Ehrenberger/publication/346097191_Carbon_Footprint_of_Magnesium_Production_and_its_Use_in_Transport_Applications/links/5fbb8dfa458515b79762c3eb/Carbon-Footprint-of-Magnesium-Production-and-its-Use-in-Transport-Applications.pdf.

IV.                    Titanium (primary): Norgate, Terry. Titanium and Other Light Metals: Technology Pathways to Sustainable Development. Accessed April 21, 2026. https://www.researchgate.net/profile/Terry-Norgate/publication/290554654_Titanium_and_other_light_metals_-_Technology_pathways_to_sustainable_development/links/5f645759458515b7cf3c07fc/Titanium-and-other-light-metals-Technology-pathways-to-sustainable-development.pdf.

V.  Titanium (secondary): IperionX. “IperionX Releases Life Cycle Assessment of 100% Recycled Titanium Powder.” 2023. https://iperionx.com/2023/04/26/iperionx-releases-life-cycle-assessment-of-100-recycled-titanium-powder/.

VI.                     Nickel (primary):

·       Roy, S., Moustafa, H., Vaidya, K. et al. Improving process granularity of life cycle inventories for battery grade nickel. npj Mater. Sustain. 3, 15 (2025). https://doi.org/10.1038/s44296-025-00059-7: https://www.nature.com/articles/s44296-025-00059-7.

·       Nickel Institute. Life Cycle Data – Executive Summary. 2024. https://nickelinstitute.org/media/r5wn5u4j/2025-lifecycledata-executive-summary.pdf.

VII.                   Nickel (secondary):

·       Transport & Environment. Nickel Recycling. February 2026. https://uploads.transportenvironment.org/production/files/2026_02_TE_report_nickel_recycling.pdf.

• Continuum Powders. Life Cycle Assessment of Nickel Powder. March 2025.  https://www.continuumpowders.com/wp-content/uploads/2025/03/Life-Cycle-Assessment-of-Nickel-Powder_Continuum-Powders.pdf.

VIII.                 Copper (primary and secondary):

·       Ekman Nilsson, Anna, Marta Macias Aragonés, Fatima Arroyo Torralvo, Vincent Dunon, Hanna Angel, Konstantinos Komnitsas, and Karin Willquist. 2017. "A Review of the Carbon Footprint of Cu and Zn Production from Primary and Secondary Sources" Minerals 7, no. 9: 168. https://doi.org/10.3390/min7090168

IX.                    Steel (primary): World Steel Association. “Sustainability Indicators.” Accessed April 21, 2026. https://worldsteel.org/wider-sustainability/sustainability-indicators/.

X.  Steel (secondary): Rashed Saeed Al Remeithi. Recycling Steel for Circular Economy: Exploring the Steel Recovery & Recyclin Rates in UAE Construction Industry. Kalifa University. MSc. Thesis. 2024. https://khazna.ku.ac.ae/ws/portalfiles/portal/32097448/file.