Financial statements follow strict rules, including accounting frameworks, internal controls, and independent audits. But if you ask most organisations how they calculate their carbon emissions, water use, or supplier diversity, the process often falls short of these standards.
ISSA 5000, the International Standard on Sustainability Assurance, will apply to periods starting on or after 15 December 2026 to help close this gap. The real question is: if someone reviewed your sustainability data as carefully as your financial data, would it stand up to scrutiny?
Same discipline, purpose-built standard
ISSA 5000 is the first assurance standard designed specifically for sustainability information, not just adapted from financial audit rules. It applies to both limited and reasonable assurance for any sustainability topic, including climate, water, biodiversity, social, and governance issues. The standard is framework-neutral, so it works with information reported under IFRS S1/S2, ESRS, GRI, or other criteria. It does not require a specific reporting framework, emissions method, or double materiality. Double materiality comes from the reporting criteria, like ESRS or CSRD, not from the assurance standard itself.
The ethical standards for practitioners have also been updated. IESBA’s International Ethics Standards for Sustainability Assurance (IESSA) now apply with ISSA 5000, setting independence and objectivity rules similar to those used in financial audits. The IAASB has announced that ISAE 3410, the old standard for greenhouse gas statements, will be withdrawn when ISSA 5000 takes effect. ISAE 3000 (Revised) will only apply to assurance work that does not involve sustainability information.
Where the discipline is harder than financial audit
This is not just financial audit standards applied to a new topic. ISSA 5000 does not set a specific materiality benchmark or percentage threshold. The term “clearly trivial” is used in the standard but is not defined. Many practitioners rely on familiar rules, like a 70–80% materiality allocation or a 5% threshold for greenhouse gas emissions, but these are not part of ISSA 5000 and come from financial audit habits. Deciding what is material for a qualitative claim, such as whether a company has included “fully integrated” climate risk into its risk management, requires professional judgment about what a reasonable user would think, not a set formula. This makes the evidence needed much harder to gather than simply checking numbers against a threshold.
What “auditable” ESG data actually requires
To meet this level of scrutiny, organisations need a clear process for deciding what is material, based on their chosen reporting criteria. They also need a traceable link from the original data to the reported numbers, similar to a general ledger trail. There should be a formal basis for the criteria and reporting boundaries, along with management sign-off and governance oversight for sustainability information, the same as required for financial statements. Most organisations created their sustainability reporting for disclosure, not for evidence. ISSA 5000 will highlight this difference.
Why this cannot wait
In South Africa, the IRBA has officially adopted ISSA 5000 and encourages early adoption. It has also released Staff Practice Alert 12 (March 2026) to help local practitioners. While sustainability assurance is still voluntary in South Africa, if a Registered Auditor does the work, IRBA’s rules already apply. This is a current requirement, not something for the future. In other African countries like Nigeria, Kenya, Egypt and Morocco, regulators are moving in the same direction, though at different speeds. Development finance institutions such as the AfDB and IFC are now adding ESG requirements to most new financing. The African Development Bank’s Integrated Safeguards System has applied to all its supported projects since May 2024. Every green bond, sustainability-linked loan, and blended finance product using this capital, needs assurance for the claims made.
The practical question
For organisations that report, the choices made now about data systems will decide if their sustainability information can be assured when required, or if it will need to be rebuilt quickly later. For practitioners, the standard is set, the ethics rules are active, and the evidence requirements are strict. The only question left is how ready each firm will be when the first engagement comes.
Financial information became credible through years of discipline, standard-setting, and independent review. Now, sustainability information is expected to meet the same standards, but in a much shorter time. The real question is not if your ESG data could be assured in theory, but if it is strong enough to pass a real test.
Sources: IAASB, ISSA 5000 (November 2024); IRBA adoption communications and Staff Practice Alert 12 (March 2026); IESBA, IESSA (January 2025); African Development Bank Integrated Safeguards System (effective 31 May 2024); Nigeria Financial Reporting Council, Nairobi Securities Exchange, Egyptian Exchange and Moroccan green economy strategy public disclosures.
