International

The International Auditing and Assurance Standards Board (IAASB) has issued ISSA 5000 General Requirements for Sustainability Assurance Engagements – an overarching standard for assurance on sustainability reporting. It is designed to be assurance practitioner and reporting framework neutral and covers both limited assurance and reasonable assurance. It draws from ISAE 3000 (Revised) Assurance Engagements Other than Audits or Reviews of Historical Financial Information, ISAE 3410 Assurance Engagements on Greenhouse Gas Statements and the Extended External Reporting (EER) Assurance guidance. As a result, the IAASB has withdrawn ISAE 3410.

ISSA 5000 requires compliance with: 

• Ethical and independence requirements that are “at least as demanding” as the International Ethical Standards Board for Accountants (IESBA) International Code of Ethics for Professional Accountants (including International Independence Standards) (the Code).
• Quality management requirements that are “at least as demanding” as ISQM 1 Quality Management for Firms That Perform Audits or Reviews of Financial Statements, or Other Assurance or Related Services Engagements.

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Australia 

The AUASB has issued ASSA 5000 General Requirements for Sustainability Assurance Engagements, which is based on ISSA 5000. The key difference is ASSA 5000 prohibits the use of direct assistance by internal audit in sustainability assurance engagements, consistent with the prohibition contained in ASA 610 for financial statement audits.

ASSA 5010 Timeline for Audits and Reviews of Information in Sustainability Reports Under the Corporations Act 2001 sets out the phasing of assurance. Entities may choose to obtain assurance at a higher level, on additional information and for earlier years than is specified.

^{* For Group 3 entities, the phasing for assurance on statements that there are no material climate-related risks and opportunities is the same as for Strategy – risks and opportunities.
** For Group 1 entities with December year-ends, they will have two ‘Year 1’s’ for assurance purposes.}

Although the timing of first-time application is different for each Group, all Groups will follow the same assurance phasing “pathway” from the first year of application.

For instance, “Year 1” in the above table is:

• Reporting periods beginning on or after 1 January 2025 for Group 1 entities (Group 1 entities with December year-ends will have two Year 1’s for assurance purposes)
• Reporting periods beginning on or after 1 July 2026 for Group 2 entities
• Reporting periods beginning on or after 1 July 2027 for Group 3 entities 

ASSA 5010 does not require the directors’ declaration on the sustainability report to be covered by assurance reports in Year 1 for any Group.

For the years commencing on or after 1 July 2030, the Corporations Act requires reasonable assurance for all mandatory climate disclosures, regardless of Group.

In the 2026–27 Federal Budget, the Australian Government indicated it will adjust assurance requirements alongside proposed changes to reporting thresholds to ensure they are proportionate and practical. As a result, fewer entities are expected to require sustainability assurance services for mandatory climate reporting. 

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New Zealand

The Financial Markets Conduct Act 2013¹ requires assurance over the GHG emissions disclosures within climate statements, and this must be conducted in accordance with sustainability assurance engagement standards issued by the XRB.

NZ CS 1 Climate related Disclosures requires that assurance over GHG emissions disclosures be provided at a minimum of limited assurance, noting that the assurance engagement may cover all, or other parts, of the climate statement.

^{[1] See Adoption Provision 4 of NZ CS 2 Adoption of Aotearoa New Zealand Climate Standards
[2] See Adoption Provision 8 of NZ CS 2 and FMA class exemption}

^{1 Amended by the Financial Sector (Climate-Related Disclosures and Other Matters) Amendment Act 2021}

The XRB has issued ISSA (NZ) 5000 Sustainability Assurance Engagement Standards (ISSA (NZ) 5000), which will apply for periods beginning on or after 15 December 2026. From that date, ISSA (NZ) 5000 will be the applicable assurance standard for GHG emissions disclosures within climate statements.

Prior to this, the XRB issued NZ SAE 1 Assurance Engagements over Greenhouse Gas Emissions Disclosures as a temporary standard. NZ SAE 1 requires such assurance engagements to be conducted in accordance with either:

• ISAE (NZ) 3410 Assurance Engagements on Greenhouse Gas Statements, or
• ISO 14064 3:2019 Greenhouse gases — Part 3: Specification with guidance for the verification and validation of greenhouse gas statements.

NZ SAE 1 and ISAE (NZ) 3410 will be revoked for periods beginning on or after 15 December 2026, coinciding with the effective date of ISSA (NZ) 5000.

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Ethics and independence requirements

Sustainability assurance requires auditors to demonstrate the same ethics and independence as required for traditional financial assurance.

International

The IESBA has issued the International Ethics Standards for Sustainability Assurance (including International Independence Standards) (IESSA) – a new stand-alone Part 5 to the Code to add ethics and independence standards for sustainability assurance engagements. Part 5 is based on Part 4A but is designed to be assurance practitioner and reporting framework neutral. The key difference between Part 4A and Part 5 is the inclusion of new independence requirements for assurance work performed at a value chain component.

Australia 

The APESB has issued the Australian Ethics Standards for Sustainability Assurance (including Independence Standards) (AESSA) which is based on the IESSA. It is effective from 1 January 2026 with a later implementation date of 1 July 2028 for provisions related to the value chain components.

New Zealand

The XRB has issued International Ethics Standards for Sustainability Assurance (including International Independence Standards) (New Zealand) within a reissued PES 1 International Code of Ethics for Assurance Practitioners (including International Independence Standards) (New Zealand), applicable for periods beginning on or after 15 December 2026, with Sections 5405 (Group Sustainability Assurance Engagements) and 5406 (Another Practitioner Whose Assurance Work is Used in a Sustainability Assurance Engagement) specifically commencing for accounting periods beginning on or after 1 July 2028.

Quality management requirements

Firms that undertake any type of assurance engagements, including sustainability assurance engagements, are required to design, implement and operate a system of quality management using a proactive risk-based approach in accordance with ASQM 1 in Australia or PES 3  in New Zealand.

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Keeping up to date 

This is a high-level summary of sustainability assurance developments as of August 2026. The landscape will continue to evolve, and members can stay up to date by visiting the Sustainability Resource Centre.