To understand the clash, it helps to start with the problem substitution is meant to solve. Many industrial processes produce more than one useful output. A corn ethanol refinery, for example, yields not only fuel but also dried distillers’ grains with solubles, a protein-rich animal feed known as DDGS. When an analyst wants to calculate the footprint of just one of these co-products, the shared upstream emissions, in this case everything from fertilizer manufacture to the energy consumed by the refinery, must somehow be divided between them. One option is allocation, which partitions the shared burdens according to some rule, such as relative mass or economic value. Substitution takes a different route: it identifies the products that the co-products displace in the market, quantifies the environmental burdens of those displaced products, and credits the avoided burdens to the product under study. In the ethanol example, because DDGS displaces dedicated soy meal production as animal feed, the emissions associated with that soy meal are subtracted from the ethanol’s ledger.

Brander’s argument rests on a precise statement of what attributional life cycle assessment, or ALCA, is supposed to represent. He identifies two defining features. First, ALCA describes the material and energy flows, and their associated impacts, from the processes that are actually used in the life cycle of the product being studied. Second, ALCA estimates the share of total absolute anthropogenic impacts that belongs to that product, a property often visualized as a slice of a pie chart. This second feature gives rise to additivity, the principle that if you calculated attributional footprints for every final product in the economy and added them up, the total should approximate the sum of all human impacts. Consequential life cycle assessment, by contrast, answers a different question entirely: it models how the world changes in response to a shift in demand, linking in whatever activities are expected to change as a consequence.

The heart of the new reply is a worked example using corn ethanol, drawing on data from a 2011 paper by Brander and Colleen Wylie. Producing a tonne of ethanol alongside 1.03 tonnes of DDGS generates 2.18 tonnes of carbon dioxide equivalent in upstream emissions. Because each tonne of DDGS displaces soy meal, the avoided burden credited to the system works out to 3.51 tonnes of carbon dioxide equivalent per tonne of ethanol. Applying substitution, the ethanol is assigned a result of minus 1.33 tonnes, a negative footprint. Provost-Savard and Majeau-Bettez had proposed a fix for the additivity problem: assign the 3.51 tonnes of avoided burden to the DDGS instead, so that the assigned values sum back to the true total of 2.18 tonnes. On the surface, the arithmetic balances.

But Brander shows that this solution fails both tests of what ALCA is meant to represent. Consider the figure of 3.51 tonnes assigned to the DDGS. That number describes the emissions from processes used in the life cycle of soy meal, not the processes used in the life cycle of DDGS, which are the refinery operations and corn cultivation that actually produced it. The result therefore does not describe the supply chain of the product it is attached to. Provost-Savard and Majeau-Bettez, Brander notes, accept this entailment of their proposal but do not appear to recognize how profound a departure it represents. If practitioners want to adopt such an alternative normative rule, he argues, they owe the community an explicit statement of what the resulting method would represent, something their paper does not provide.

The second failure is even more visually striking. A share of total impacts cannot exceed 100 percent or fall below zero. Yet the value assigned to the DDGS, 3.51 tonnes, is greater than the entire absolute impact of the combined system, 2.18 tonnes. And the value assigned to the ethanol, minus 1.33 tonnes, is negative. As Brander puts it, when dividing a pie it is impossible to give one person a negative slice. He is careful to pre-empt a misunderstanding here: the objection is not that life cycle results can never be negative, since genuine carbon removals or albedo effects can produce net negative totals, but rather that a share of any effect, positive or negative, cannot logically be less than zero percent or more than 100 percent of that effect. Notably, Provost-Savard and Majeau-Bettez themselves state that ALCA should represent shares of total impacts, without recognizing that their own solution produces values that cannot be shares.

The reply also tackles the argument that any absolute value can be expressed as a change relative to some reference state, which was central to the 2024 defense of substitution. Brander shows that this framing creates a strange hybrid when substitution results are carried into further analyses. If the change value is assigned to one product and the reference value to another, summing them recovers only the total for the described state, not separate absolute values for each co-product, which lands the analyst back at the original multifunctionality problem. Alternatively, treating displacement as a property of the state, suitable for allocation like mass or economic value, fails because substitution is not actually apportioning shares of the absolute flows, as the out-of-range results demonstrate. On the question of marginal data, he observes that the rationale for using it, representing the market mechanism of a transition, is inherently consequential, answering what changes rather than what exists.

Perhaps the most technically interesting section addresses functional unit expansion, a rival technique that Provost-Savard and Majeau-Bettez had invoked to argue that substitution must be legitimate. Functional unit expansion widens the object of study to include the functions of the co-products, so the functional unit becomes one tonne of ethanol plus 1.03 tonnes of DDGS, avoiding allocation altogether. It is a long-established result, dating to work by Anne-Marie Tillman and colleagues in 1994, that substitution and functional unit expansion yield identical outcomes in comparative analyses, because comparing ethanol with petrol requires ensuring both systems deliver the same functions, including animal feed. Brander confirms the numerical equivalence in this context but insists it does not make the techniques methodologically equivalent. Outside comparisons, ALCA serves other purposes, such as quantifying contributions to absolute sustainability thresholds or feeding into further assessments. If a negative ethanol result were used as an input to another product’s footprint, the final number would simply fail to describe the emissions of the processes involved. Functional unit expansion does not create this problem; substitution does.

The stakes of this methodological quarrel extend well beyond the journals. Brander and Wylie called fifteen years ago for standards and guidance documents to state clearly that substitution should not be used in attributional assessment, yet the recommendation was never implemented, and practitioners continue to report results whose coherence the new paper calls into question. The reply closes with a renewed call for the life cycle community to confront the issue and for existing standards, including ISO 14044, which has been criticized elsewhere for conflating substitution with system expansion, to be updated. Whether the appeal gains traction may depend on whether the field agrees with Brander’s central claim: that before defending a technique, its advocates must first say, precisely, what the numbers are supposed to mean. Until then, some of the carbon footprints printed on products and enshrined in corporate reports may rest on arithmetic that cannot describe any share of the world’s actual impacts.

Subject of Research: The compatibility of substitution with attributional life cycle assessment methodology

Article Title: Substitution is not consistent with attributional life cycle assessment: reply to Provost-Savard and Majeau-Bettez (2024)

Article References: Brander, M. (2026). Substitution is not consistent with attributional life cycle assessment: reply to Provost-Savard and Majeau-Bettez (2024). Journal of Industrial Ecology, 30(4), 1779-1785. https://doi.org/10.1007/s44498-026-00121-0

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00121-0

Keywords: life cycle assessment, substitution, attributional LCA, consequential LCA, carbon footprint, multifunctionality, allocation, system expansion, ISO 14044, Greenhouse Gas Protocol, industrial ecology, methodology

The problem the researchers address is known as multifunctionality. Many industrial processes are inherently multitaskers. A waste incineration plant does not simply dispose of trash; it may generate electricity and heat, and its leftover bottom ash may contain recoverable metals and minerals. In life cycle assessment, any process with more than one functional flow—whether a product output or a waste input that is being treated—must be handled carefully, because the environmental burdens and benefits of the process need to be distributed among its multiple functions. Conventional LCA has developed a toolkit for this over decades, including allocation methods that partition impacts by mass or economic value, and substitution approaches that credit a coproduct for displacing an alternative product elsewhere in the economy.

What makes pLCA fundamentally harder is time. In a conventional assessment, the analyst can observe the process as it exists today and classify each flow with reasonable confidence. In a prospective assessment, the process may not yet exist at industrial scale, and the economic and regulatory environment around it may shift dramatically before it does. The authors highlight a striking example: waste heat that is considered a nonfunctional byproduct at laboratory scale may become a valuable, marketable product once the process is upscaled and integrated into district heating networks. A flow that is a waste today can become a product tomorrow, and that single reclassification can change whether a process counts as multifunctional at all—and therefore how its impacts are calculated.

Earlier work had already established foundations for dealing with these questions. Guinée and colleagues proposed a four-step approach for identifying and handling multifunctional processes in LCA, moving from distinguishing product and waste flows, to identifying functional flows, to spotting multifunctional processes, to handling them with a chosen procedure. Separately, Langkau and colleagues introduced the SIMPL approach, a stepwise framework for scenario-based inventory modeling in prospective LCA. But the SIMPL approach explicitly excludes the uncertainties tied to multifunctionality decisions, and reviews have found that the identification and handling of multifunctional processes in pLCA studies is often inconsistent, incomplete, or missing altogether. The new guidance is designed to fill precisely that gap by weaving the four-step multifunctionality approach into the three iterative steps of SIMPL.

The resulting framework is built around sub-steps attached to the first and fourth steps of the Guinée approach. In the identification phase, practitioners are guided to identify the external key factors—political, economic, social, technological, environmental, and legal influences—that could change the type of each flow or the number of functional flows in the future. They then develop explicit future assumptions about these changes and integrate them into consistent future scenarios. In the handling phase, the same logic is applied to the parameters that govern how multifunctionality is resolved: the substituted product, the substitution ratio, and the allocation factors. For each handling procedure—system expansion, substitution, physical allocation, or economic allocation—the guidance provides tailored recommendations for identifying what could change and building those changes into scenarios.

Each procedure carries its own distinctive vulnerabilities to the future. System expansion, which redefines the system boundaries to include all functions of the process, is comparatively insensitive to future variability in a non-comparative study, though the authors note that analysts should still verify that goals and scopes align with future scenarios. Substitution, by contrast, is highly sensitive: the substitution ratio, defined as the functionality of the coproduct divided by the functionality of the substituted product, can shift as coproduct quality, input composition, and production technology evolve. Physical allocation depends on the physical relationships between functional flows, which may change through process upscaling, learning curves, and economies of scale. Economic allocation is arguably the most volatile of all, because it rests on relative revenues that fluctuate with commodity prices, patents, technology diffusion, and inflation—yet many published pLCAs apply static revenue ratios that freeze today’s market conditions into a model of tomorrow.

To demonstrate the framework in action, the researchers applied it to a novel process for valorizing incinerator bottom slag, the residual ash left after municipal waste combustion in Germany. Today, most of this slag ends up in landfill construction, but it contains minerals and metals that could be recovered as high-quality secondary raw materials. The process under study uses selective milling followed by magnetic, eddy current, and density separation to yield three fractions: minerals, iron, and non-ferrous metals. The recovered minerals can substitute natural resources in cement production, with the pre-calcinated calcium oxide content reducing carbon dioxide emissions by replacing calcium carbonate. Because the process has only been tested discontinuously at laboratory scale and is unlikely to reach industrial operation before 2030, it is a textbook candidate for prospective assessment.

The team convened a scenario workshop with seven industry representatives spanning waste incineration, slag processing, plant engineering, and cement production to apply the guidance. The workshop revealed how regulatory and quality considerations could flip flow classifications: a minerals stream currently classified as waste under German construction regulations could become a product if metal separation improves or regulations change, while an iron-rich stream’s status depends on whether it is landfilled or used as copper ore. The researchers ultimately built ten foreground scenarios—covering system expansion, three substitution variants, three physical allocation variants, and three economic allocation variants—and combined each with three background scenarios for 2030 generated with the premise tool based on ecoinvent data and the REMIND integrated assessment model, yielding thirty scenario combinations evaluated with the superstructure approach.

The results carry a message that should unsettle anyone who assumes background energy scenarios are the dominant source of uncertainty in future-facing assessments. Within a single foreground scenario, switching between background datasets changed the climate impact by at most 12 kilograms of carbon dioxide equivalents per metric ton of treated slag. But varying the foreground assumptions within the same handling procedure produced far larger swings: 109 kilograms for substitution and 30 kilograms for economic allocation. Most strikingly, in the substitution case, the choice of foreground scenario could reverse the sign of the result entirely, flipping the process from a net carbon sink to a net emitter. In other words, the methodological assumptions about how multifunctionality is handled can matter more than the choice of future energy system.

The authors are careful to note that this finding comes from a single case study and should not be generalized, since sensitivity patterns depend on system characteristics and temporal scope. They also acknowledge practical limitations: the framework depends on expert and stakeholder participation, generates a combinatorial explosion of potential scenarios that requires subjective judgment to prune, and currently keeps the multifunctionality handling procedure fixed across background scenarios. Yet the core contribution stands. By making the invisible choices visible—documenting which assumptions about flow types, substitution ratios, and allocation factors underlie a result—the guidance supports more transparent and reproducible pLCA, particularly for dynamic systems such as energy-intensive electrification projects. For decision-makers weighing investments in emerging green technologies, the study is a reminder that the environmental verdict on the future depends not only on what the world will look like, but on the small, consequential choices analysts make when modeling it.

Subject of Research: A stepwise methodological framework for handling multifunctionality and its uncertainties in prospective life cycle assessment

Article Title: Stepwise guidance for tackling multifunctionality challenges in prospective life cycle assessment

Article References: Zacharopoulos, L., Thonemann, N., Steubing, B., Guinée, J., & Geldermann, J. (2026). Stepwise guidance for tackling multifunctionality challenges in prospective life cycle assessment. Journal of Industrial Ecology, 30(4), 1885-1901. https://doi.org/10.1007/s44498-026-00128-7

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00128-7

Keywords: prospective life cycle assessment, multifunctionality, life cycle assessment, uncertainty analysis, scenario development, substitution, allocation, waste incineration, slag valorization, industrial ecology, circular economy, integrated assessment models

The stakes are considerable. The regulation mandates that the carbon footprint method align with the Product Environmental Footprint Category Rules for rechargeable batteries, and it authorises the European Commission to fix the details through Delegated Acts. A draft of the Delegated Act for electric vehicle batteries was released for public consultation in April 2024 and is still being refined. Because every manufacturer will have to follow the same standardised method, any ambiguity in that method translates directly into numbers that cannot be fairly compared across companies. The Braunschweig team, led by Jana Husmann, Johanna Holsten, Gabriela Ventura Silva and Christoph Herrmann, set out to find precisely where those ambiguities bite hardest, using a simulation-based case study of a 100 MWh battery cell production plant in Germany.

Battery cell production is an energy-hungry, multi-stage affair. It begins with mixing dry powders—active materials, carbon black, binders—with solvent, then coating the slurry onto foil substrates, drying and calendering the coated electrodes, and cutting them to size. The anodes and cathodes are then assembled into cells through packaging, final drying, contacting, electrolyte filling and tempering, all inside conditioned dry rooms whose humidity control alone demands enormous amounts of energy. The chain ends with formation, the charging and discharging that activates each cell’s electrochemistry. Because primary data from large-scale plants are rarely accessible, the researchers built a dynamic process chain simulation combining agent-based and discrete event approaches, capturing material and energy flows, machine behaviour, scrap rates and even the fluctuating energy demand of the dry room over time. The functional unit was a single battery cell of 33.3 Wh nominal capacity produced in Germany in 2023, assessed with the EF v3.1 method for climate change.

The first methodological minefield the study explores is multifunctionality—the situation where a single process delivers more than one product or service. For years, battery cell production was treated as a single-function process: it makes cells, full stop. But with the regulation’s mandatory recycled content targets and the industry’s circular economy ambitions, former waste streams are acquiring economic value. Non-functional cells rejected in final testing and scrap electrodes from coating and cutting steps are increasingly attractive feedstocks for recyclers, not least because electrodes can be directly recycled before the electrolyte is ever added. Once those waste flows become products in their own right, the environmental burdens of production must somehow be divided between the good cells and the scrap.

The researchers tested several ways of drawing that dividing line. The cut-off approach simply lets the waste leave the production system without any impacts attached; whoever recycles it and uses the secondary material carries the recycling burden. The circular footprint formula, or CFF, favoured by the PEFCR, splits burdens and benefits of recycling between the battery being recycled and the one made with recycled content, governed by parameters such as recycled content, recycling rate and material quality. The draft Delegated Act adds a special variant, the CFF PS, tailored to production scrap recycling. Finally, classical allocation based on mass or economic value distributes upstream production impacts between cells and scrap. The baseline result with cut-off was 6.3 kilograms of CO2-equivalent per cell. Between cut-off, CFF and CFF PS, impacts differed by less than one percent—but full allocation pushed the figure roughly six percent higher, because the waste cells and electrodes, which account for about eight percent of production impacts under the other approaches, no longer carried their share.

That six percent swing may sound modest, but multiplied across gigawatt-hours of production and scrutinised against regulatory thresholds, it matters enormously for comparability. The authors also found that allocation creates a deeper modelling problem: if recycled scrap re-enters production and is recycled again, the impacts assigned to materials change with every recycling loop, requiring detailed tracking and tracing of materials that is currently not feasible. Statistical modelling of how materials circulate could estimate these effects, but the researchers argue that any such approach would need standardised rules for documentation to keep companies comparable. Economic allocation, meanwhile, is largely ruled out in practice, since the guidelines permit it only when the value of final cells or electrodes is ten times that of the waste—unlikely given that both share identical production processes and costs.

The team’s recommendation is pointed: treat production scrap exactly like end-of-life batteries, and preferably use the cut-off approach. Their reasoning is consistency. The CFF, they argue, is complex, mixes product and material perspectives, leaves room for interpretation in its parameters, and would likely be applied inconsistently by different practitioners. More strikingly, they identified a substantive flaw: the default recycling processes in the draft Delegated Act do not recover lithium, even though the EU Batteries Regulation sets explicit targets for lithium recycling rates and recycled content. The cut-off approach, by contrast, is simpler, needs less data, and aligns with the many battery and cross-industry guidelines that already favour it. Only the CFF captures both recycled content and recycling rate, but the authors note that regulatory compliance on those targets will most likely be demonstrated through certificates and tools such as the battery passport, not through the carbon footprint calculation itself.

The second axis of the study concerns data aggregation, and here the findings are equally consequential. When the researchers varied temporal aggregation—averaging production data over a month, a day, or an hour of March 2023—they found that daily and hourly figures deviated from the monthly baseline by around plus or minus ten percent. The variation stems from processing energy, dry room energy demand, and the number of scrap cells produced in each period, all of which fluctuate with weather, electricity mix and production rhythm. Monthly or yearly averages smooth out these outliers and best represent long-term conditions, making them suitable for official reporting. Hourly and daily resolution, however, is what engineers need to spot inefficiencies, plan production, and integrate renewable energy sources—insights that vanish entirely in an annual average.

Spatial aggregation told a different story. Whether data were collected machine by machine, by factory area, or for the whole plant, the total climate impact per cell barely changed. What changed dramatically was the ability to locate hotspots. Machine-level data revealed that dry room energy and cathode dry mixing are major contributors; area-level data could only point to broad sections like cell production; factory-level data reduced the analysis to materials, energy and scrap. Since the regulation aims not just at reporting but at continuous improvement of carbon footprints, recycling rates and recycled content, the authors warn that a standard focused solely on reporting would squander LCA’s engineering potential. They propose that the methodology could require finer data collection internally without mandating public disclosure at that resolution.

On the question of how the mandatory one-year data collection period should be defined—calendar year or rolling year backwards from production—the study offers a concrete compromise: a rolling average updated monthly. For cells produced in March 2026, for example, the average of data from March 2025 to February 2026 would apply. This preserves the robustness of a full-year basis and comparability between companies, while incentivising detailed data collection and reflecting decarbonisation efforts, supplier changes and process improvements far more quickly than a fixed calendar year. Taken together, the study’s message is clear: before Europe’s battery carbon footprint rules are finalised, regulators must resolve how multifunctionality is handled, clarify the data collection period, and decide whether the CFF’s complexity is fit for large-scale implementation—or whether the humbler cut-off approach, and a method that serves engineering as well as reporting, would serve the energy transition better.

Subject of Research: Life cycle assessment methodology for battery cell production under the EU Batteries Regulation

Article Title: Life cycle assessment of battery cell production in the context of the European Union batteries regulation: the influence of data aggregation and multifunctionality handling

Article References: Husmann, J., Holsten, J., Ventura Silva, G., & Herrmann, C. (2026). Life cycle assessment of battery cell production in the context of the European Union batteries regulation: the influence of data aggregation and multifunctionality handling. Journal of Industrial Ecology. https://doi.org/10.1007/s44498-026-00169-y

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00169-y

Keywords: life cycle assessment, battery cell production, EU Batteries Regulation, carbon footprint, multifunctionality, data aggregation, circular footprint formula, cut-off approach, recycling, lithium-ion batteries, production scrap, industrial ecology