Every scope 3 number ends up on an auditor's desk

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Every scope 3 number ends up on an auditor's desk

Every scope 3 number ends up on an auditor's desk

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Published: July 21, 2026 |

Carbon accounting is changing. What was once largely the domain of sustainability teams is quickly becoming a finance, governance and assurance priority as organisations prepare for mandatory climate reporting. It's no longer enough to calculate emissions; organisations increasingly need to explain where those numbers came from, how they were calculated and whether they can withstand independent scrutiny.

That's especially true for Scope 3 emissions. The data may sit across procurement systems, supplier networks and operational activities, but the expectation is increasingly the same as for financial reporting: the numbers must be transparent, traceable and defensible. Put simply, every Scope 3 number eventually ends up on an auditor's desk.

Through our work supporting organisations preparing for mandatory sustainability reporting, we've observed a common challenge: many businesses still rely on fragmented data, manual processes, and undocumented methodologies, even as expectations are rising. To help organisations build a more reliable and defensible approach to carbon accounting, BDO has partnered with Avarni, combining sustainability reporting expertise with technology that improves traceability, transparency, and confidence in emissions reporting.

Carbon accounting is entering a new era

For many organisations, carbon accounting began as a way to understand and manage environmental impact. Today, it carries a much broader responsibility. As climate disclosures become part of mainstream corporate reporting, emissions data is increasingly subject to the same scrutiny as financial information. Boards want confidence in the numbers. Auditors want evidence. Regulators expect transparency. Investors expect consistency.

That shift is exposing a reality for many organisations: measuring emissions is only part of the challenge. The harder question is whether the data, methodologies and assumptions behind those numbers can stand up to review. Organisations that once focused on simply calculating emissions are now focusing on how they govern, document and defend them.

It's a natural evolution. As sustainability reporting matures, carbon accounting is becoming less about producing an emissions inventory and more about producing information that stakeholders can trust.

Four questions every auditor will ask about your emissions data

So, what does an auditor actually look for when reviewing emissions data?

Despite the technical nature of emissions reporting, the underlying principles are relatively straightforward. Organisations need to be able to demonstrate that their disclosures are complete, prepared consistently, supported by evidence and capable of withstanding scrutiny. In many ways, it's the same discipline that underpins good financial reporting.

These are the four core questions that can help organisations build a stronger foundation for carbon accounting and sustainability reporting:

It's difficult to have confidence in emissions data if there's uncertainty about what's been included and what's been left out. Organisations need to be able to demonstrate that reporting boundaries are clearly defined, relevant emissions sources have been identified, and the underlying data tells a complete story. Even small gaps can raise questions about the reliability of the overall result.

Carbon accounting isn't just about this year's numbers. Stakeholders also want confidence that emissions can be compared meaningfully over time. Consistent methodologies, assumptions and reporting boundaries help organisations explain trends, demonstrate progress and avoid unnecessary questions when results change from one period to the next.

Few carbon calculations are entirely straightforward. Estimates, assumptions and judgement all play a role. What matters is being able to clearly explain how decisions were made and why. Transparency creates confidence in reported results and helps ensure important information isn't locked away in spreadsheets or internal knowledge.

Perhaps the most important test of all is whether the organisation can stand behind its decisions. Whether it's setting reporting boundaries, selecting data sources, or determining what is and isn't material, there should be a clear, documented rationale. If someone asks, "Why did you do it that way?", there should be a clear answer.

Together, these principles help organisations move beyond simply calculating emissions and towards something more important: confidence in the information they're reporting. When an auditor asks, "How did you get to that number?", organisations should be able to answer with confidence. These four principles provide the foundation for doing exactly that.