Carbon Footprint of Metal Production Underestimated

Metal production emissions may be drastically underestimated

A new peer-reviewed study from the University of St Andrews has found that standard carbon accounting methods seriously underestimate emissions from metal production. The research suggests that copper production emissions could be more than ten times higher than conventional estimates once acid mine drainage is properly accounted for.

The findings matter because metals are central to both existing infrastructure and the net-zero transition. However, the climate impact of mining has been measured incompletely. This study identifies a large emissions source that has been systematically excluded from carbon footprints and corporate disclosures.

For UK businesses buying metal-intensive products or reporting supply chain emissions, the research raises questions about the accuracy of existing data. Companies relying on conventional lifecycle assessments may be significantly underreporting their true carbon exposure.

Acid mine drainage creates long-term CO2 emissions

The University of St Andrews research, published in Environmental Science and Technology, provides the first comprehensive quantification of CO2 emissions from neutralising acid mine drainage in metal mining. The study examined copper production in a specific mining region and found that emissions from drainage treatment matched the entire conventional carbon footprint of copper production in that area.

The research team estimates that total emissions will exceed conventional estimates by more than tenfold once all sulfide-bearing material has weathered and generated drainage requiring treatment. This represents a fundamental gap in how mining emissions are currently measured and reported.

Acid mine drainage occurs when sulfide minerals are exposed during mining operations. These minerals react with water and oxygen to produce acidic runoff. Consequently, mine operators must neutralise this acidity using lime or other alkaline reagents. Both the chemical reaction itself and the production of these reagents generate substantial CO2 emissions.

This is not a marginal issue affecting only a few sites. Acid mine drainage is a widespread and long-running consequence of sulfide mineral extraction. Many mine sites continue generating acidic drainage decades after active mining has ceased. Therefore, the emissions from neutralisation treatments accumulate over timescales far longer than typical carbon accounting periods.

Earlier research had already indicated the scale of the problem. A 2025 study estimated annual CO2 emissions from drainage neutralisation at between 20 and 90 gigagrams per year. This figure represented anywhere from 20% to 1,400% of conventional mining carbon footprints in the catchments examined. Similarly, U.S. research documented measurable CO2 fluxes from acid mine drainage sites, confirming that these emissions are real and quantifiable.

Metal production already accounts for major global emissions

Metals are already recognised as a significant climate concern. The steel sector produces approximately 2.18 tonnes of CO2 equivalent per tonne of steel on average. Total emissions from steel production reach around 4.1 billion tonnes of CO2 equivalent annually. Depending on measurement boundaries, steel accounts for roughly 7% to 11% of global CO2 emissions.

Against this backdrop, the St Andrews findings suggest that mining-related emissions inventories are missing an important component. The omission is particularly significant for metals extracted from sulfide-rich ore bodies, where acid mine drainage is most prevalent. This includes not only copper but also other base metals and some precious metals.

The research highlights a systematic problem with current carbon accounting standards. Most lifecycle assessments focus on direct mining operations, processing, and transport. However, they typically exclude long-term environmental remediation and ongoing treatment obligations. This creates a gap between reported emissions and actual climate impact.

For businesses, this matters because metal content is embedded throughout supply chains. Manufacturing, construction, electronics, and infrastructure all depend on mined metals. If the carbon footprint of these materials has been underestimated by an order of magnitude, then downstream emissions calculations are also understated.

Implications for UK businesses and supply chain reporting

UK companies face increasing requirements to measure and report supply chain emissions. The government’s Procurement Policy Note 06/21 requires suppliers bidding for major contracts to publish carbon reduction plans. Moreover, mandatory climate-related financial disclosures are expanding to cover more businesses. These obligations depend on accurate emissions data from suppliers and product lifecycles.

If conventional metal production footprints are too low by a factor of ten, businesses may be underreporting their Scope 3 emissions significantly. This creates both compliance risk and reputational exposure. Furthermore, companies setting science-based targets need reliable baseline data. Inaccurate inputs undermine the credibility of reduction commitments.

The findings also affect procurement decisions. Businesses increasingly use embodied carbon as a criterion when selecting suppliers or materials. However, if primary metal producers are not accounting for acid mine drainage emissions, buyers cannot make informed comparisons. This disadvantages suppliers who invest in better measurement and disclosure.

Additionally, the research strengthens the case for circular economy approaches. Recycled metals generally have much lower emissions than primary production. Recycling avoids the mining phase entirely, eliminating acid mine drainage and associated treatment obligations. For businesses looking to reduce supply chain emissions, increasing recycled content becomes more attractive as the true cost of virgin material becomes clearer.

The study also has implications for environmental management systems and due diligence. Companies may need to ask more detailed questions about how suppliers calculate carbon footprints. Specifically, businesses should verify whether mining-related emissions include long-term remediation and treatment. This is particularly important for sectors with high metal intensity, such as construction, automotive, and electronics.

What the study reveals about carbon accounting gaps

The University of St Andrews research identifies several key issues that affect how mining emissions are reported and understood.

• Standard carbon accounting methods for metal production have systematically excluded CO2 released during acid mine drainage neutralisation.
• Emissions from drainage treatment in the studied region already match the entire conventional carbon footprint of copper production in that area.
• Once all sulfide-bearing material has weathered, total emissions from drainage neutralisation will exceed conventional copper production footprints by more than tenfold.
• Acid mine drainage is a long-term consequence of sulfide mineral mining that continues for decades after active extraction ends.
• Neutralising acidic drainage requires lime or other alkaline reagents, which generate CO2 through both chemical reactions and production processes.
• Earlier studies have estimated annual CO2 emissions from drainage neutralisation at 20 to 90 gigagrams per year, representing up to 1,400% of conventional mining footprints in some catchments.
• The findings apply not only to copper but potentially to other metals produced from sulfide-bearing deposits where acid mine drainage is common.

Climate policy may be based on incomplete baselines

One of the central concerns raised by the research is that climate policy and industrial decarbonisation targets may rely on emissions baselines that are too optimistic. If mining emissions have been systematically underestimated, then sector-specific reduction pathways may be less ambitious than they appear.

This matters for national climate commitments and carbon budgets. The UK has legislated a target to reach net zero emissions by 2050. Achieving this requires accurate measurement of current emissions across all sectors. If industrial emissions are higher than reported, the remaining carbon budget is correspondingly smaller.

The issue also affects carbon pricing mechanisms and border adjustment proposals. These systems depend on reliable emissions factors to function properly. If metal production footprints are understated, carbon costs will be too low. This reduces the incentive to invest in lower-carbon alternatives and undermines the effectiveness of pricing policies.

For mine operators, the findings create potential reporting obligations. Companies may need to revisit their emissions inventories and include acid mine drainage neutralisation in their carbon disclosures. This could substantially increase reported emissions for some operations. However, it would also provide a more accurate picture of long-term environmental liabilities.

The research also has implications for investment decisions. Financial institutions increasingly assess climate risk when evaluating mining projects. If conventional carbon footprints underestimate emissions by an order of magnitude, the climate risk profile of primary metal production is higher than currently modelled. This could affect project financing, insurance costs, and asset valuations.

Furthermore, the study highlights the importance of including end-of-life and remediation obligations in lifecycle assessments. Mining creates long-term commitments that extend far beyond operational timescales. Carbon accounting methods need to capture these extended responsibilities to reflect true climate impact.

Reducing dependence on primary metal production

The research adds weight to arguments for reducing reliance on virgin metal extraction where alternatives exist. Recycled metals offer substantially lower emissions because they avoid the mining phase entirely. This eliminates acid mine drainage and associated treatment obligations from the outset.

For businesses, increasing recycled content in purchased materials can significantly reduce supply chain emissions. This is particularly relevant for metals where recycling rates are already high, such as steel and aluminium. Specifying recycled content in procurement policies becomes more compelling as the true carbon cost of primary production becomes clearer.

However, not all metals can be fully substituted with recycled alternatives. Demand for metals is growing, driven partly by the net-zero transition itself. Electric vehicles, renewable energy infrastructure, and grid upgrades all require substantial quantities of copper, steel, and other metals. Meeting this demand will require some primary production alongside expanded recycling.

This creates a need for better mining practices and more complete carbon accounting. If primary production is necessary, operators should measure and report all associated emissions, including long-term remediation. Transparency allows buyers to make informed decisions and creates incentives for lower-impact extraction methods.

The findings also support efforts to develop lower-carbon mining technologies. For example, alternative neutralisation methods or acid mine drainage prevention techniques could reduce the CO2 released during treatment. Similarly, using renewable energy for processing and transport can lower the overall footprint of metal production. Nevertheless, these improvements require accurate measurement of current emissions to assess their effectiveness.

Authoritative sources and further information

The research discussed in this article was published in Environmental Science and Technology, a peer-reviewed journal covering environmental chemistry and engineering. The study was conducted by researchers at the University of St Andrews and represents the first comprehensive quantification of CO2 emissions from acid mine drainage neutralisation in metal mining.

For businesses seeking guidance on supply chain emissions reporting, the UK government provides detailed requirements through Procurement Policy Note 06/21. This sets out expectations for carbon reduction plans in public sector supply chains. Additionally, government environmental reporting guidelines offer frameworks for measuring and disclosing emissions.

The UK’s net-zero strategy and sector-specific decarbonisation pathways are published by the Department for Energy Security and Net Zero. These documents provide context for understanding how industrial emissions fit within national climate commitments and reduction targets.