Thailand Mandatory Climate Disclosure: ISSB 2026

Thailand’s ESG disclosure regime is shifting from voluntary to mandatory. Under the Securities and Exchange Commission’s “ISSB Roadmap,” SET-listed companies are being moved toward disclosure fully aligned with the ISSB Standards — IFRS S1 and IFRS S2 — beginning with large-cap companies from 2026. For boards, sustainability teams, and investor-relations functions, this is not a cosmetic change: climate reporting moves from “comply or explain” to a mandatory regime that regulators, index providers, and global investors will scrutinise.

From “comply or explain” to mandatory

Thailand has run a “comply or explain” model, where disclosure gaps could be explained rather than closed. The SEC’s ISSB Roadmap changes that — transitioning to a mandatory disclosure regime aligned with the ISSB Standards, led by climate-related disclosure (IFRS S2). Large-cap listed companies are first, from 2026, with the requirement expected to phase across the broader market thereafter. If you are a large SET-listed company, the practical question is no longer whether to disclose climate data, but whether your disclosure will withstand assurance. See what SET-listed companies must disclose under IFRS S1 and S2.

Where it lands: the 56-1 One Report

ESG disclosures are made annually in Form 56-1 One Report. The sustainability section of that filing is where your IFRS S1/S2 climate content will sit — governance, strategy, risk management, and metrics and targets. Getting the structure right there is what turns raw sustainability data into a defensible regulatory disclosure. See how to approach the 56-1 One Report ESG section.

New SET tools: ESG Data Platform & SET Carbon

To ease the transition, SET has launched the ESG Data Platform and SET Carbon — tools that help listed businesses improve sustainability disclosure and track greenhouse-gas emissions, integrated to reduce duplication of work. They are a genuine help for data collection. But the outputs are inputs: emissions figures and platform data still need to be turned into a clear, audit-ready narrative disclosure. Start from a robust Scope 1, 2 & 3 GHG inventory before you draft.

What “mandatory” actually changes in practice

The move from voluntary to mandatory disclosure shifts the standard of care applied to every climate statement you publish. Under a voluntary regime, an incomplete or optimistic disclosure carried mainly reputational risk. Under a mandatory, assurance-oriented regime aligned with the ISSB Standards, the same disclosure becomes a regulated filing — one that must be internally consistent, supported by documented methodology, and defensible if challenged. In practical terms, three things change for the sustainability and IR functions.

• Evidence, not assertion. Every material claim — an emissions figure, a target, a transition commitment — needs a documented basis a reviewer can trace back to source data. “We are committed to net zero” is no longer sufficient without the supporting pathway.
• Consistency across documents. The same metric must read identically in the 56-1 One Report, the sustainability report, the investor deck, and any rating submission. Divergent numbers across documents are the fastest way to undermine a disclosure.
• Board accountability. Because IFRS S1/S2 is built on a governance pillar, directors are expected to demonstrate active oversight of climate risk — not delegate it entirely to a sustainability team.

The four IFRS S2 pillars, applied to a Thai filing

IFRS S2 organises climate disclosure around the same four pillars familiar from the TCFD framework. Mapping your 56-1 One Report ESG section to these pillars from the outset makes the eventual assurance process far smoother.

• Governance — the board and management processes used to identify and oversee climate-related risks and opportunities, including how climate sits within existing committee structures.
• Strategy — the effect of climate risks and opportunities on the business model and financial planning, supported by scenario analysis and, where relevant, a transition plan.
• Risk management — how climate risks are identified, assessed, prioritised and integrated into enterprise risk management, rather than treated as a standalone sustainability exercise.
• Metrics and targets — Scope 1, 2 and 3 greenhouse-gas emissions, internal carbon pricing where used, and the targets against which the company measures progress.

The FTSE Russell overlay

Running in parallel, SET is upgrading its ESG Ratings by adopting the FTSE Russell ESG model, with full implementation expected in 2026. That means the same disclosure feeds two audiences at once: the mandatory regulatory filing and your ESG rating. Weak or inconsistent disclosure now costs you twice. See what the SET move to FTSE Russell ESG scores means for boards.

Why bilingual accuracy is now a compliance issue

Here is the part most companies underestimate. Filings are prepared in Thai; FTSE Russell, MSCI, and global investors read your disclosure in English. When the Thai and English versions drift — a hedged commitment stated as firm, a metric defined differently, a boundary described inconsistently — you have a misstated disclosure and a weaker rating, from the same document. Under a mandatory regime, that is a compliance exposure, not a translation nicety. ISO 17100-certified bilingual disclosure, produced by specialists who understand IFRS S1/S2 language, closes that gap.

The risk is subtle because it rarely comes from an obvious mistranslation. It comes from register and precision. A Thai phrase that reads as an aspiration can, translated carelessly, harden into a firm commitment the company never intended to make — or, conversely, a definite target can soften into vague intention, costing scored indicators. Emissions boundaries, base years, and the scope of a target are exactly the details where a small wording difference between the Thai and English versions creates a genuine discrepancy between two “official” versions of the same regulated filing. Reconciling the two languages against a single agreed meaning — rather than translating one after the other — is what prevents that drift.

What to do in the second half of 2026

• Confirm your cohort — establish whether you fall in the first mandatory (large-cap) wave.
• Run a gap analysis against IFRS S1 and S2, honestly, against what assurance will require.
• Build or refresh your GHG inventory (Scope 1, 2 and 3) — SET Carbon can feed this.
• Draft the climate disclosure for the 56-1 One Report ESG section against the four IFRS S2 pillars.
• Produce filing-ready Thai and English versions in parallel — reconciled, not sequentially translated.

Frequently asked questions

When does mandatory climate disclosure start in Thailand? Under the SEC’s ISSB Roadmap, mandatory, ISSB-aligned climate disclosure is expected to begin with large-cap SET-listed companies from 2026, phasing across the broader market thereafter. Because transitional details are still being finalised, confirm your specific cohort and timing with the SEC and your auditors.

Is IFRS S1 also mandatory, or only IFRS S2? The roadmap is led by climate-related disclosure under IFRS S2, with IFRS S1’s general sustainability-disclosure requirements forming the surrounding framework. Both should be treated as the direction of travel for large issuers.

Do the Thai and English versions both need to be accurate? Yes. The Thai version is the regulatory filing; the English version is what global investors and rating providers read. Any drift between them is a disclosure and rating risk under a mandatory regime.

Prepare your mandatory climate disclosure with the right partner

Othello International is an ISO 17100-certified bilingual ESG-disclosure and translation firm for SET-listed companies. We help boards close the IFRS S1/S2 gap and produce disclosures that read correctly — and identically — in both languages. Explore our ESG disclosure advisory or talk to our team.

📘 Free resource: Explore The FTSE 2026 Playbook Library — Othello’s ESG disclosure playbook plus focused editions for Thai banks, energy, property, healthcare, technology and more.

Related services from Othello International

Othello International is a Bangkok-based bilingual (EN↔TH) technical translation and ESG advisory firm. Related specialist services:

• climate & IFRS S2 disclosure — TCFD four-pillar
• ESG disclosure translation — IFRS S2, GRI, FTSE-ready
• GHG inventory — Scope 1/2/3, TGO-aligned
• ESG ratings submissions — FTSE, MSCI, S&P, SET