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Level 1/Carbon Accounting Fundamentals
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The GHG Protocol

The standard behind almost every corporate footprint: its five principles, organisational and operational boundaries, and the base year that makes progress measurable.

10 min read · Jacob Willis, Net Zero Lead · Last reviewed July 2026

Nearly every corporate carbon footprint on Earth follows one rulebook: the GHG Protocol Corporate Standard, developed by the World Resources Institute and the World Business Council for Sustainable Development, and adopted so universally that its vocabulary (the scopes you already know) simply is the field's vocabulary. This lesson covers the parts of the Protocol beyond the scopes that decide whether a footprint is defensible: the five principles auditors test against, the boundary choices that determine whose emissions are yours, and the base year that makes progress a measurable claim rather than a mood.

The five principles

The Protocol judges every accounting decision against five principles, and they are worth knowing verbatim because verifiers use them as their checklist:

  • Relevance: the inventory reflects the organisation's real emissions and serves its users' decisions.
  • Completeness: everything inside the chosen boundary is counted; exclusions are disclosed and justified, not silent.
  • Consistency: methods and boundaries stay comparable over time, with changes documented and history restated.
  • Transparency: assumptions, factors and methods are stated so a third party could retrace the work.
  • Accuracy: systematic bias is avoided and uncertainty reduced as far as practicable.

If they sound familiar, they should: they are the M&V course's evidence discipline restated for carbon, and the same instincts satisfy both.

Organisational boundaries: whose emissions are yours

Before counting anything, an organisation with subsidiaries, joint ventures or shared sites must choose how to draw itself. The Protocol offers three approaches: equity share (account for emissions in proportion to ownership), financial control or operational control (account for 100% of whatever you control, by the chosen definition). Operational control is the commonest choice in practice, partly because it matches how energy data arrives: the sites whose meters you hold are usually the sites you operate. The choice can move big numbers (a 50%-owned plant is half yours under equity share, all or nothing under control), so it is declared once, applied everywhere, and changed only with restatement. It is the system-boundary lesson wearing a corporate structure.

Operational boundaries and the base year

With the organisation drawn, the operational boundary decides which scopes are reported: scopes 1 and 2 are mandatory under the Protocol; scope 3 is encouraged, category by category, with a materiality-first mindset. Then the base year anchors progress: a chosen reference year whose footprint targets are measured against, with a recalculation policy for the events that would otherwise make comparisons dishonest, acquisitions, divestments and methodology changes chief among them. A company that buys another does not get to report its combined footprint against its old solo base year; the base year is restated as if the acquisition had always been there. This machinery is what separates "we cut emissions 20%" as a verifiable claim from the same words as marketing.

Worked example — the boundary choice, moving real tonnes
Given
  • A group owns 100% of factory A (2,000 tCO₂e), 50% of joint-venture factory B (3,000 tCO₂e) which it operates, and 30% of factory C (1,000 tCO₂e) which it does not operate
Find
The group's scope 1+2 inventory under equity share versus operational control.
The Protocol is a consistency machine

Scopes, principles, boundaries, base years: every piece of the GHG Protocol exists to make one organisation's number comparable with another's and with its own past. That is what buyers' questionnaires, SECR reviewers and verification bodies are actually testing when they probe a footprint, and it is why the declared choices (boundary approach, base year, exclusions) matter more than any individual factor. Get the frame right and the arithmetic is easy; get it wrong and no arithmetic can save the claim.

What's next

One Protocol question is thorny enough to earn its own lesson: when you buy electricity, do you count the grid you are physically plugged into, or the contract you signed? The next lesson covers market versus location-based scope 2, REGOs, and what "100% renewable" does and does not mean.

Sources and further reading