How Does Assurance Work Under IFRS S1/S2 Sustainability Reporting?

Why Does Assurance Matter for IFRS S1/S2 Disclosures?

Investors and other users of sustainability disclosures rely on the information being accurate and complete, much as they rely on audited financial statements. Assurance provides that independent check. As IFRS S1/S2 disclosures move from voluntary to mandatory in more jurisdictions, regulators are increasingly building assurance requirements into the compliance framework — recognizing that disclosure without verification carries less weight for investment decision-making.

What Are the Levels of Assurance?

Assurance engagements generally fall into two categories, both defined by international assurance standards rather than the ISSB itself:

• Limited assurance — the assurance provider performs procedures designed to identify whether anything has come to their attention indicating the disclosure is materially misstated. This results in a conclusion expressed in negative form (for example, "nothing has come to our attention that causes us to believe...").
• Reasonable assurance — a more extensive level of testing, comparable in rigor to a financial statement audit, resulting in a positive conclusion (for example, "in our opinion, the disclosure is fairly presented").

Many jurisdictions phasing in assurance requirements start with limited assurance and move toward reasonable assurance over subsequent reporting cycles, mirroring the phased approach many took with the underlying disclosure mandate itself. The specific assurance level, phase-in timeline, and scope (for example, whether Scope 3 emissions are included) vary by jurisdiction and should be confirmed against the applicable local rule.

Who Can Provide Assurance?

Jurisdictions differ on whether sustainability assurance must be provided by a traditional financial statement auditor, can be provided by another qualified independent assurance provider, or can be provided by either. This is an active area of regulatory development globally, and companies should confirm the applicable rule in each jurisdiction where they report rather than assuming their financial auditor is automatically permitted — or required — to provide sustainability assurance.

What Does Assurance-Readiness Actually Require?

Being ready for assurance is different from simply producing a disclosure. Assurance providers need to test underlying data, processes, and controls, which means assurance-readiness typically requires:

• Documented data collection processes for GHG emissions and other disclosed metrics, with a clear audit trail from source data to reported figure.
• Internal controls over sustainability data, comparable in principle to internal controls over financial reporting, covering data capture, aggregation, and review.
• Consistent methodology applied period over period, with any changes in methodology documented and explained.
• Governance evidence — board or committee meeting minutes, risk register entries, and other documentation that supports the governance and risk management disclosures, not just the metrics.
• Scenario analysis documentation for IFRS S2, showing the basis, inputs, and outputs of the climate scenarios used to test strategic resilience.

Companies that build these elements into their reporting process from the outset — rather than retrofitting them once assurance becomes mandatory — generally face a smoother transition when assurance requirements phase in.

How Does Assurance-Readiness Connect to the Broader Compliance Journey?

Assurance readiness should not be treated as a separate, later-stage project. It is most efficient when built into the disclosure design process from the start, following directly from the gap analysis described in How to Start Your IFRS S1/S2 Compliance Journey: A Gap Analysis Guide. A gap analysis that identifies data and control gaps early gives a company time to close them before assurance is mandatory, rather than scrambling once a regulator's assurance requirement takes effect.

How Semtrio Supports Assurance Readiness

Semtrio's IFRS S1/S2 advisory service includes assurance-readiness preparation as a core workstream — building the data architecture, documentation, and internal controls that an assurance provider will test, ahead of any mandatory assurance deadline.

Semtrio Note: As a CDP Accredited Solutions Provider, Semtrio works routinely with the data verification standards CDP applies to corporate emissions disclosures — discipline that transfers directly into preparing clients' GHG data for external assurance under IFRS S2.

Frequently Asked Questions

Does the ISSB require assurance for IFRS S1/S2 disclosures?

No. The ISSB sets the disclosure standards themselves but does not set assurance requirements — those are determined independently by each jurisdiction's regulator.

What is the difference between limited and reasonable assurance?

Limited assurance results in a negative-form conclusion based on more limited procedures, while reasonable assurance involves more extensive testing and results in a positive-form opinion, comparable in rigor to a financial statement audit.

Who is allowed to provide assurance over IFRS S1/S2 disclosures?

This depends on the jurisdiction — some permit only financial statement auditors, others permit a wider range of qualified independent assurance providers. The applicable rule should be confirmed jurisdiction by jurisdiction.

When should a company start preparing for assurance?

Ideally during the initial gap analysis and disclosure design phase, rather than waiting until an assurance mandate takes effect, since building data and control documentation retroactively is more difficult.

Does assurance typically cover Scope 3 emissions?

Assurance scope, including whether Scope 3 emissions are covered, varies by jurisdiction and phase-in stage; this should be confirmed against the applicable local rule.

If your organization needs to prepare its IFRS S1/S2 disclosures for external assurance, Semtrio can assess your current data and control environment and build a readiness plan. Contact Semtrio to discuss your assurance timeline.