Carbon Commons
​If you asked 5 different financial accountants to calculate your yearly tax bill, they should all follow the same rules on taxable income and come up with the same amount. But if you ask 5 different carbon accountants to calculate your emissions, you'll likely get 5 different answers using 5 different methods. Carbon Commons will address this fundamental problem by setting a common and open standard for carbon accounting so that the level of emissions from different products and companies can finally be compared and used by different companies as products travel across a supply chain.
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What is Carbon Commons?
Carbon Commons is an open-source (licenced) dataset of ‘hybridised’ emissions factors for any organisation to use to produce a reliable carbon footprint or emissions factor for their organisation based on activity or financial data, with data sourced and updated collaboratively. For the first time, these emissions factors will be compatible with other products, services and organisations, and with a transparent methodology that combines (hybridises) the best of the two main carbon accounting approaches – the specificity of detailed but inherently incomplete product life cycle assessments, and the full, system-complete supply chain emissions derived from input-output models.
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Carbon Commons is a step-change in global supply chain carbon accounting. Using the financial accounts that all companies already have available, it will make carbon accounting accessible, transparent, and for the first time, comparable for companies across all supply chains, allowing a supplier's emissions to be accounted for in their customer's emissions.
The project launched at London Climate Action Week in June 2025, with Sage, our insights and financial partners and the British Business Bank. Once the initial dataset is published, SWC will consult with users and industry in parallel with the development of a larger dataset for release later in 2025/26.
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Carbon Commons is being launched by Sage, Small World Consulting and the British Business Bank, working as partners.
om hybrid lenses.
“ It’s great to see the launch of the Carbon Commons approach - a practical and methodologically robust accounting approach which addresses many of the challenges we have seen in supply chain carbon accounting. We have been working Small World Consulting since 2012, using this approach and now hope that others will follow the Carbon Commons approach resulting in a less fragmented and more coherent carbon accounting landscape”
Gabrielle Ginér, Head of environmental sustainability, BT Group.
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The benefits to SMBs of supply chain carbon accounting
A company’s emissions are broken into 3 different types, called Scopes. Scope 1 is primarily direct emissions from fuels that they burn. Scope 2 are indirect emissions from fuels burnt to generate the electricity (and other forms of energy) they use. And upstream Scope 3 are primarily the indirect emissions from everything that the company buys or sources from its supply chain.
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Supply chain emissions are usually significant and cannot be left out of any carbon reporting process. The CDP estimates that on average, Scope 3 accounts for around three-quarters of a company’s overall emissions, but this varies greatly between different industries.
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Quantifying emissions across its supply chain enables an organisation to see any hotspots, so they can prioritise areas for emission reductions. It also allows them to set meaningful reduction targets, often resulting in efficiencies and reduced resource use. Examining the emissions from a supply chain is also a crucial part of identifying and managing the risks associated with suppliers.
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Supply chain or Scope 3 carbon accounting is also important in order to comply with reporting regulations, and increasingly for stakeholder engagement, where key clients further up the supply chain are asking for the emissions from their suppliers.
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This example shows some of the supply chain of a mobile phone. Each product in the supply chain has Scope 1 and 2 emissions from the energy used in its production, and Scope 3 from the emissions associated with its supply chain. When a company buys this product, eg a battery, to use as part of its product, e.g. a mobile phone, all of the battery's Scope 1, 2 and 3 emissions are included in the Scope 3 emissions of the mobile phone's supply chain.
The problem with carbon accounting
Clearly, accounting for emissions across the full supply chain is increasingly important and beneficial to small and medium businesses (SMBs) as well as larger corporates. But reporting on Scope 3 is still voluntary for SMBs, partly because of the perceived difficulties for small businesses in gathering the right data, and the inconsistent nature of Scope 3 emissions calculations.
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How we use your spend data to calculate your carbon footprint, how we combine this with LCAs and what Scopes 1, 2 and 3 mean.
There are problems with both of the main types of supply chain carbon accounting:
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Limitations of Product Life Cycle Analysis (P-LCA)
Product Life Cycle Analysis (P-LCA) works from the bottom up, assessing the emissions with each tier of production. Because the supply chain is infinite (every tier is supplied by the preceding tier), and because P-LCAs are a resource-intensive process, there is an inherent limit to the emissions that can be accounted for; this is called a ‘truncation error’. The system boundary, or the number of tiers in the supply chain, is therefore incomplete. Different P-LCAs are likely to have different system boundaries, all incomplete in differing ways.
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Added to the incomplete nature of P-LCAs, is the problem of having limited access to supplier-specific data, and even difficulties in tracking down the exact suppliers used in complex, global supply chains. Even where adequate P-LCAs do exist, there is then an additional resource pressure in maintaining them and collating them in one accessible dataset.
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Limitations of input-output models
Input-output models do solve the problem of incomplete system boundaries that are inherent with P-LCAs; indeed, by their very nature, they account for emissions from all sectors of the economy as a whole. But they introduce other problems, predominantly that they lack specificity, meaning that they fail to distinguish between particular products or processes (e.g. a virgin versus recycled material). They also provide emissions factors, not at a product or organisation level, but an average for one industry sector in one country. This means that changing supplier to one with lower emissions is not reflected in the standard emissions factor for that purchase from an input-output model.
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How 'hybridisation' solves the limitations of P-LCAs and input-output models
Hybridisation means carefully combining data from both P-LCAs and input-output models, to solve the problem of incomplete system boundaries, whilst keeping the specificity benefits from P-LCAs.
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The first step is to examine a P-LCA and determine its system boundary, how many tiers of the supply chain does it cover, and which parts are missing? The missing parts are then added from the industry sector average emissions from an input-output model.
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Hybridisation determines the system boundary of a P-LCA and how much of the emissions have been truncated from the complete system boundary shown by an Input-Output model. If the P-LCA boundary only covers 33% of the complete emissions shown by an input-output model, the truncation adjustment factor = 3.
How Carbon Commons solves supply chain carbon accounting problems
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Eliminates truncation errors in P-LCAs by hybridising them with input-output models to make the boundaries cover all the emissions, system-complete.
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Hybridises by adding the truncated emissions missing from a P-LCA using input-output model data.
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Assesses all LCA and IO methods and calculations against clear and transparent criteria.
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Provides an easy-to-use hybridised dataset of the most used emissions factors in an activity-based (e.g. per kWh, per km) and spend-based (e.g. per pound, per dollar) format.
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Provides open access to a central database for commercial and non-commercial users, promoting global adoption of the same data and standards.
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“ Supporting initiatives that advance technical best practices in carbon accounting is a core objective of the CAA, so we’re delighted to be partnered with SWC and Sage on the Carbon Commons project to develop a hybridised approach to scope 3 emissions measurement that may help solve challenges that carbon accounting professionals face on a daily basis in quantifying complex supply chains in a scalable and robust way.”
Andrew Griffiths, Co-Founder, Carbon Accounting Alliance.
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Carbon Commons principles
We have 5 principles that will drive Carbon Commons, helping it achieve its aim to make supply chain carbon accounting consistent, realistic, practical, and trustworthy.
Transparency
Completeness
Independence
Accessible
to all
Quality and Governance
Transparency
The derivation of emissions factors and other results should be traceable and transparent, including methods, assumptions and, ideally, input data and calculations.
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Completeness
​Analysis of company and product supply chains (upstream scope 3) and resulting emissions intensity factors must be system-complete without double counting.
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Independence
Research and analysis should be as independent as possible from interests that could gain from particular results. Any direct or indirect interests must be clearly declared.
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​Accessible to all
Emissions factors should be practically available and affordable for all users, consistent with adequate resourcing of the maintenance and evolution of high-quality methods, guidance and datasets.
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Quality and Governance
All methods and emissions factors must be quality-assessed by an independent body that is overseen by a robust system of governance.
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“ This partnership is an important step in ensuring robust and consistent carbon accounting for UK companies.We fully support the ambition of Carbon Commons as it will allow company reporting to align with sector-level benchmarks and the UK's national climate ambitions to be net zero by 2050.”
Prof John Barrett, Leeds University.
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Who is involved in Carbon Commons?
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Small World Consulting
World-leading climate consultancy with expertise in measuring the carbon footprint and environmental impacts of organisations, led by Prof Mike Berners-Lee.
www.sw-consulting.co.uk
Sage Group PLC
Leading British multinational enterprise software company which specialises in providing cloud-based business management solutions, including accounting, payroll, HR, and payment systems, primarily for small and medium-sized businesses.
www.sage.com
British Business Bank
The UK’s economic development bank, whose mission is to drive sustainable growth and prosperity across the UK, and to enable the transition to a net zero economy, by improving access to finance for smaller businesses.
www.british-business-bank.co.uk
The Carbon Accounting Alliance
Represents the carbon accounting community with over 750 companies in over 60 countries. Carbon Commons has been met with enthusiasm and a high level of interest from the community: www.carbonaccountingalliance.com
We Mean Business Coalition
A global non-profit coalition formed by seven leading no-profits (BSR, CDP, Ceres, Corporate Leaders Group, Climate Group, The B Team, WBCSD) and working to catalyse business and policy action on climate change: www.wemeanbusinesscoalition.org
B4NZ
A supporting institution of the UN-convened Net Zero Banking Alliance (NZBA), it focuses on strategic policy alignment to enable policymakers and banks to play their part in accelerating the transition to net zero:
www.unepfi.org/net-zero-banking
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How do I get involved in Carbon Commons?
We're actively looking for new Carbon Commons partners and supporters across the private and public sectors, NGOs and academic bodies. If you support the aims of an open-source, globally compatible emissions factor database, and want to get involved or show your support in any way, we’d like to hear from you.
Early partners and supporters will gain a unique opportunity to demonstrate climate leadership, elevate their brand visibility, and shape the future of sustainable business practices worldwide.
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Supporter: Endorse the aims of the project and be an advocate, not involved in operations.
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Partner: Active in decision making, and willing to share resources, expertise and some of the project workload.
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Funder: Contribute to the development of the open-source database and the global promotion of its adoption, opportunities for brand visibility.
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