Practitioners given practical guidance as landmark sustainability assurance standard takes effect

Sustainability assurance professionals are entering a pivotal new phase in 2026, with a groundbreaking global standard for assuring climate, social and governance information for investors now coming into force.

As organisations increasingly rely on targets, transition plans and forward-looking disclosures to inform investors and other stakeholders, assurance over this information has become both more important and more complex.

To support the profession through this major shift, two leading global accountancy bodies have published a report to assist practitioners' professional judgement when dealing with estimates and forward-looking information in sustainability assurance engagements.

Estimates and forward-looking information are central to sustainability reporting. Targets, transition plans, and projections now play a key role in informing decisions by investors and other stakeholders. At the same time, such information is inherently uncertain and dependent on professional judgement, assumptions and future events that may not be within an organisation's control.

As sustainability reporting continues to evolve, so too does the need for credible, decision-useful assurance over this information. The introduction of ISSA 5000 General Requirements for Sustainability Assurance Engagements provides a global framework for assurance over sustainability information, including estimates and forward-looking information.

Applying this framework effectively requires careful professional judgement, particularly where evidence is forward-looking and outcomes cannot be verified at the reporting date.

A case study: Demystifying the assurance of estimates and forward-looking information in accordance with ISSA 5000 produced by ACCA (the Association of Chartered Certified Accountants) and CA ANZ (Chartered Accountants Australia and New Zealand) supports the application of that professional judgement in practice. It focuses on how assurance practitioners can respond to this inherent uncertainty in estimates and forward-looking information when performing engagements in accordance with ISSA 5000.

Antonis Diolas, Head of Audit and Assurance, Policy & Insights, ACCA said: 'This report reinforces a critical distinction: assurance over such information relates to its preparation and disclosure, not to whether future outcomes will ultimately be achieved. Our work in this area underlines how the role of the accountant is being redefined.'

Amir Ghandar, Reporting and Assurance Leader, CA ANZ, said: 'By bringing the requirements on estimates and forward-looking information together and grounding them in a practical case study, this report provides -much needed guidance for assurance practitioners. Most importantly, it reinforces the central role of professional judgement in delivering assurance that users can actually rely- on.'

The report takes the form of a case study focussing on how practitioners respond to identified risks, perform procedures appropriate to the level of assurance, whether limited or reasonable, and evaluate evidence and uncertainty.

It also highlights how issues identified in relation to the underlying estimates and forward-looking information may affect the overall assurance conclusion.

Read the report.

Note to editors
The report is the second part of a series exploring the application of ISSA 5000. The first was A case study: Demystifying materiality in accordance with ISSA 5000