Three primary standards in lockstep. GHG Protocol Corporate Standard (revised edition, World Resources Institute + WBCSD) for organisational and operational boundary methodology; GHG Protocol Corporate Value Chain (Scope 3) Standard for the 15-category Scope 3 architecture; GHG Protocol Scope 2 Guidance (2015) for dual location + market-based reporting. Plus ISO 14064-1 (organisational quantification and reporting) for verification-grade rigour, with ISO 14064-3 (validation and verification specification) applied at the methodology level so the inventory is verification-ready.

For GWP factors, IPCC AR6 GWP100 (Sixth Assessment Report, published 2021) is the default — superseding AR5 and AR4. Older base years are recalculated to AR6 with the conversion documented. For Thailand-specific submissions, TGO national methodology is reconciled separately (typically uses AR5 with specific Thai grid factors). For financial-services category 15, PCAF Global GHG Accounting and Reporting Standard for the Financial Industry is applied.

The two methods reflect different views of the same electricity purchase. Location-based uses the average emission factor of the electricity grid where the consumption physically occurs — for Thai operations, this is the Thai national grid factor published by TGO. The method reflects the company’s actual contribution to grid-average emissions. Market-based uses supplier-specific or instrument-backed factors that the company can substantiate — Power Purchase Agreements (PPAs), Renewable Energy Certificates (RECs/I-RECs/T-RECs), supplier-specific emission factors, or residual-mix factors for the unused portion.

The GHG Protocol Scope 2 Guidance (2015) requires both methods to be disclosed. Market-based is where renewable energy procurement (PPAs, RECs) shows up as Scope 2 reduction. Location-based remains unchanged regardless of renewable procurement. For companies with significant renewable PPAs, the gap between the two methods can be substantial — and the disclosure of both is required for IFRS S2 § 29(a), GRI 305-2, FTSE Russell, and CDP. Misreporting only one of the two is a common error.

The GHG Protocol Corporate Value Chain Standard defines five relevance tests applied per category: (1) Size — does the category contribute significantly to total Scope 3 emissions; (2) Influence — does the company have potential to influence emission reduction in the category; (3) Risk — does the category contribute to climate-related risk exposure; (4) Stakeholders — do stakeholders (investors, customers, regulators) consider the category relevant; (5) Outsourcing — does the category include outsourced activities that used to be in Scope 1 or 2.

A category is material if it passes any of the five tests. For most SET-listed companies, 5–9 of the 15 categories are material; the remainder are reasonably excluded with the determination documented. IFRS S2 § 29(a) does not require all 15 categories — it requires disclosure of material categories with the materiality determination documented. The Scope 3 Materiality Determination deliverable provides this documentation. The most-commonly-included categories for non-financial SET-listed companies: 1 (Purchased Goods), 3 (Fuel-and-Energy), 4 (Upstream Transport), 7 (Employee Commuting), 11 (Use of Sold Products), 12 (End-of-Life). For financial services, category 15 (Investments) is the dominant category requiring PCAF methodology.

The most-commonly-flagged gap for SET-listed companies entering IFRS S2 in 2026 is Scope 3 incompleteness. The typical pre-2025 SET-listed inventory disclosed Scope 1, location-based Scope 2, and 2–3 of the easier Scope 3 categories (typically 6 Business Travel, 7 Employee Commuting, sometimes 1 Purchased Goods using spend-based factors).

The gap signature looks like: category 1 (Purchased Goods) disclosed at spend-based factor only — needs uplift to supplier-specific or average-data Tier 2 factors; category 3 (Fuel-and-Energy) not disclosed at all (often missed because it’s not visible to procurement); category 4 (Upstream Transport) incomplete; category 11 (Use of Sold Products) not disclosed for manufacturers despite being typically the largest category; category 12 (End-of-Life) not disclosed. The Standard Tier engagement closes the gap by adding the typically-missing categories with appropriate data-quality tier per category. The disclosure narrative documents which categories are excluded and why — required for § 29(a) defensibility.

The Thailand GHG Management Organization (TGO) operates Thailand’s national GHG accounting and management programmes: Carbon Footprint of Organization (CFO), Carbon Footprint of Product (CFP), T-VER voluntary carbon market, and the Carbon Neutrality / Net-Zero certification programmes. The TGO methodology uses specific Thai grid emission factors, specific Thai industrial process factors, and historically IPCC AR5 GWP factors — which produce different inventory totals than international GHG Protocol + AR6 inventories.

SET-listed companies typically submit to TGO programmes (CFO most commonly) AND publish international inventories for IFRS S2 / GRI / CDP / FTSE consumption. The two inventories should reconcile — but routinely don’t, because the methodology differences aren’t well-managed. The TGO Reconciliation Memo deliverable explicitly walks the differences: emission factor differences, GWP differences, scope/boundary differences (TGO may exclude certain Scope 3 categories), reporting period alignment. Drafted by in-house TGO CFO + CFP Auditor. Catches the issue before rating agency or auditor challenges it.

Where Othello has drafted the inventory, external assurance (AA1000AS or ISO 14064-3) must be performed by a third party for independence. Othello cannot draft and assure the same inventory in the same engagement. Where Othello has drafted the inventory, the engagement coordinates the external assurer (Bureau Veritas, DNV, SGS, LRQA, BSI, TÜV, etc.) — supplying the verification preparation pack, responding to assurer queries, and supporting the assurance process — but the assurance opinion is issued by the third party.

Where Othello is separately engaged for AA1000AS or ISO 14064-3 assurance on an inventory drafted by another firm, the in-house AA1000AS ACSAP and ISO 14064 Lead Auditor can perform the assurance directly. Conflict-of-interest checks run at engagement intake. AA1000AS service → · ISO 14064-3 verification service →

Base year recalculation is required when structural changes occur that affect inventory comparability without reflecting actual emission performance. The GHG Protocol identifies three triggers: (1) structural changes — M&A, divestiture, outsourcing/insourcing; (2) methodology changes — new emission factors, calculation methodology updates (e.g., GWP AR5 → AR6 transition), Scope 3 category additions; (3) discovery of errors — significant errors in prior-year inventory data discovered through verification.

The company sets a significance threshold for recalculation — 5% of total Scope 1+2 emissions is typical. Below the threshold, prior-year inventories are kept unchanged with the change disclosed; above the threshold, the base year is recalculated and re-stated. The Boundary & Methodology Memo documents the threshold and tests structural changes against it. The most common SET-listed trigger is the GWP AR5 → AR6 transition — which technically requires recalculation but is often missed; Othello applies AR6 by default and recalculates prior-year base year accordingly.

The Science Based Targets initiative (SBTi) validation process requires the company to submit its inventory methodology, base year emissions, and prior-year emissions trajectory as part of the target validation submission. SBTi reviews the inventory completeness against its requirements before validating any near-term or net-zero target.

Key SBTi inventory requirements: (1) Scope 3 coverage — categories representing ≥40% of total Scope 3 emissions must be included in the inventory boundary; (2) base year — preferably no earlier than two years prior to commitment date; (3) data quality — minimum data quality requirements per category (PCAF data quality tiers 1–5 used as reference); (4) verification — SBTi increasingly expects third-party assurance of base year emissions for net-zero targets. Greenfield Tier inventory engagement typically precedes SBTi commitment by 1–2 quarters to ensure these requirements are met. SBTi Pathway service →

Yes. Othello responds to formal procurement processes for GHG inventory engagements from SET-listed corporates, prospective listing applicants, post-M&A integration teams, SBTi committers, and procurement teams scoping larger ESG advisory engagements. Standard procurement requirements are met: ISO 17100:2015 certification, in-house ISO 14064 Lead Auditor (CQI/IRCA accredited) — the same credential external verifiers hold; in-house TGO CFO + CFP Auditor for Thai national reconciliation; in-house AA1000AS ACSAP for assurance-readiness; IFRS Foundation S2 certification for disclosure narrative alignment; VERRA Lead Assessor + CORSIA Verifier for voluntary carbon market reconciliation; PCAF methodology capability for financial-services category 15; GDPR + PDPA compliance; mutual NDA from first email; and SET-listed engagement references available under mutual NDA at procurement stage.

Standard RFP response is 3–5 วันทำการ. RFP response covers: methodology approach (GHG Protocol + ISO 14064-1 + 14064-3-defensible drafting), boundary methodology, Scope 3 materiality determination approach, data hierarchy approach, emission factor source selection, tier recommendation per scenario, in-house bench credentials, capacity allocation, pricing structure, engagement timeline, and sample inventory excerpt (anonymised). Quote response on engagement scoping is within one business hour of receipt of source files and signed NDA.