Sustainability assurance: limited vs reasonable

Financial statements are audited. Most ESG data is not, or is checked far less thoroughly. Sustainability assurance is the process by which an independent provider examines ESG information and gives a conclusion on whether it can be relied on.

There are two levels. Reasonable assurance is close to an audit: the provider does extensive testing and gives a positive opinion. Limited assurance is lighter: the provider does fewer procedures and says only that nothing came to its attention to suggest the data is wrong. Most ESG assurance in the world today is limited.

In India, BRSR Core indicators must be independently assessed or assured for the largest listed companies. Knowing what kind of check was done, by whom and against which standard, tells you how much weight to put on the numbers.

Limited and reasonable assurance

Global standards

• ISAE 3000 (Revised): the IAASB's general standard for assurance on non-financial information
• ISAE 3410: the IAASB's standard for assurance on greenhouse gas statements
• ISSA 5000: the IAASB's new overarching standard for sustainability assurance, issued in November 2024, effective for periods beginning on or after 15 December 2026
• Other standards: ISO 14064-3 for verification of GHG statements, often used by certification bodies, and AA1000AS from AccountAbility

Indian standards

• ICAI's SSAE 3000 (assurance on sustainability information) and SAE 3410 (assurance on GHG statements) are the current standards for Indian chartered accountants.
• In 2026, ICAI approved SSA 5000, aligned with ISSA 5000 with some India-specific changes. It applies to financial years beginning on or after 1 April 2027, when SSAE 3000 and SAE 3410 will be withdrawn. ICAI developed it in discussion with SEBI.

BRSR Core: assessment or assurance

Since SEBI's March 2025 circular, companies can choose either assurance under recognised assurance standards, or an assessment under standards developed by the Industry Standards Forum (ASSOCHAM, CII and FICCI) in consultation with SEBI.