Why Are These Mistakes So Common?
GHG accounting is a relatively new discipline for most companies. While financial accounting has been governed by standardized rules for centuries, carbon accounting has only slightly more than a decade of history, and many companies are building these processes for the first time. The GHG Protocol (WRI/WBCSD, 2004) and ISO 14064-1 (ISO, 2018) standards provide a strong framework, but the same mistakes are repeatedly made during implementation.
The cost of these mistakes is not trivial. An incorrect emissions figure can delay SBTi target validation, lower CDP scores, create problems during CSRD assurance audits, or cause financial losses in CBAM reporting. Here are the seven most common mistakes and how to avoid each.
Mistake 1: Wrong Organizational Boundary Definition
The GHG Protocol offers two main approaches: equity share and control (operational control or financial control). Choosing the wrong approach can significantly change total emission figures.
Real-world scenario: A Turkish conglomerate has five subsidiaries and three joint ventures. When reporting under the equity share approach, the 50 percent stake in joint ventures is proportionally reflected in emissions. Under the operational control approach, only facilities where control lies with the parent company are included — joint ventures may be completely excluded. The difference can reach 20-30 percent of total emissions.
Fix: Select the approach that best fits your organizational structure and apply it consistently. Document the choice and do not change it between years. If your joint venture and subsidiary structure is complex, prepare a policy document that clearly defines the consolidation method (GHG Protocol Corporate Standard, Chapter 3).
Mistake 2: Skipping Scope 3 Categories
Many companies limit their Scope 3 reporting to business travel (Category 6) or employee commuting (Category 7). These two categories typically represent 2-5 percent of total Scope 3 emissions. The real major items — purchased goods and services (Category 1), upstream transportation (Category 4), use of sold products (Category 11) — are overlooked.
Real-world scenario: A manufacturing company reports Scope 3 only as business travel (500 tCO2e annually). When all categories are screened, Category 1 (purchased raw materials) emissions alone turn out to be 45,000 tCO2e. During a CDP questionnaire or SBTi validation, this gap seriously undermines reporting credibility.
Fix: Screen all 15 categories defined in the GHG Protocol Scope 3 Standard. Conduct a spend-based preliminary analysis to identify and prioritize the largest categories. You do not need to calculate all categories in detail in the first year — but you do need to document which ones are significant through a screening exercise (WRI/WBCSD, 2011).
Mistake 3: Outdated Emission Factors
Using the same emission factors for years produces misleading results, particularly for parameters that change annually such as electricity grid emission factors. Turkey's grid emission factor has decreased significantly in recent years alongside the growth in renewable energy capacity.
Real-world scenario: A company uses Turkey's 2020 grid emission factor (0.50 kgCO2/kWh) in 2025 as well. The current factor is approximately 0.45 kgCO2/kWh. For a facility consuming 100,000 MWh of electricity, this difference means an overstatement of 5,000 tCO2e per year — and the emissions reduction trend is distorted.
Fix: Update emission factors every reporting period. Defra/DESNZ conversion factors are updated annually. The IPCC emission factor database, national inventory guidelines, and TEIAS/TurkStat data for Turkey are reliable sources (Defra/DESNZ, 2025). Document the source and year for each factor.
Mistake 4: Double Counting
Reporting the same emissions in multiple scopes or categories. Particularly common in two areas:
Between Scope 2 and Scope 3 Category 3: Under the Scope 2 market-based method, zero emissions are reported using renewable energy certificates (YEK-G, I-REC). But the same company calculates Scope 3 Category 3 (fuel and energy-related activities) using the grid average — in this case, the renewable energy effect is counted twice.
In intra-group transactions: A subsidiary's Scope 1 emissions also appear in the parent company's Scope 3 Category 1 (purchased goods) — creating double counting risk in consolidation.
Fix: Clearly understand the definition of each scope and category. Apply elimination rules in group consolidation. Ensure certificates used in Scope 2 market-based method are not double-counted in Scope 3. Reference the GHG Protocol's "avoiding double counting" guidance.
Mistake 5: Inconsistent Base Year
Failing to recalculate the base year when structural changes occur (mergers, acquisitions, divestments, new facility openings) invalidates year-over-year comparisons. A claim of "our emissions fell 20 percent" that stems from having sold a large factory is not real decarbonization.
Real-world scenario: A company set targets with a 2020 base year. In 2023, it divests an energy-intensive facility. Without base year recalculation, the divestment-driven reduction appears as genuine decarbonization. When this is detected during SBTi validation, targets need to be recalculated.
Fix: Define a base year recalculation policy. The GHG Protocol recommends updating the base year when structural changes affect total emissions by more than 5-10 percent. This threshold should be set according to your company's size and volatility (GHG Protocol Corporate Standard, Chapter 5). Document the policy in writing and apply consistently.
Mistake 6: Only One Scope 2 Method
The GHG Protocol Scope 2 Guidance has required both location-based and market-based reporting since its 2015 update. Many companies report only one — typically whichever produces the lower figure.
Why both are needed: The location-based method reflects the carbon intensity of the grid where the company physically operates — showing the geographic reality of emissions. The market-based method reflects the company's energy procurement decisions (PPAs, green tariffs, renewable energy certificates) — showing the impact of active management.
Different frameworks prefer different methods: CSRD/ESRS E1 mandates both methods. SBTi uses the market-based method for targets. CDP accepts both but expects consistency. Reporting only one method means failing to meet the other framework's requirements (GHG Protocol Scope 2 Guidance, 2015).
Fix: Calculate and report both methods. Clearly state the reason for the difference (renewable energy certificates, PPAs).
Mistake 7: Insufficient Documentation
If the rationale for emission factor selection, assumptions made, and data sources used are not documented, verification and assurance audit processes become significantly more difficult. This may be the "most dangerous" mistake — because even if the emissions figure is correct, an undocumented calculation can be rejected in an assurance audit.
Real-world scenario: A company is preparing its GHG inventory for the third year. The employee who performed the first two years' calculations has left. Which emission factors were selected, what assumptions were made for Scope 3, and the rationale for the base year calculation are documented nowhere. The new team has serious difficulty ensuring backward consistency. In the CSRD assurance audit, the auditor cannot confirm the accuracy of undocumented calculations.
Fix: Prepare a methodology note for each calculation. Minimum documentation should cover: data source (invoice, meter reading, supplier declaration), emission factor reference (IPCC, Defra, national source) and year, calculation steps (formula, conversion multipliers), data quality assessment (measurement, estimate, or default value), and assumptions and limitations. ISO 14064-1:2018 clearly defines documentation requirements. This documentation ensures organizational memory continuity and prevents knowledge loss during personnel changes.
Checklist: At the Start of Each Annual Inventory Cycle
To systematically prevent these seven mistakes, review this checklist at the beginning of each reporting cycle:
- Organizational boundary approach selected, documented, and consistent with previous year
- All 15 Scope 3 categories screened and significant ones identified
- Emission factors from current reporting period (source and date specified)
- Double counting risk checked (especially Scope 2-3 interface and intra-group transactions)
- Structural changes evaluated and base year recalculated if needed
- Scope 2 calculated both location-based and market-based
- Methodology note prepared for each calculation (data source, factor, assumption)
- Audit trail established (traceability from raw data to final figure)
Action Item: Each of these seven mistakes directly affects the reliability and audit-readiness of your reporting. The good news: every one of them has a straightforward fix — but only when detected. Reviewing this list at the start of your annual inventory cycle is far more productive than saying "if only" at the end of the year.
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