Mandatory Climate Reporting Assurance in Australia 2026: ASSA 5000, ASSA 5010, and What Businesses Must Know

Australia's mandatory climate reporting regime is now a reality, and with it comes a new and demanding set of assurance obligations for auditors and the entities they serve. The first wave of Group 1 entities lodged sustainability reports for financial years ending 30 June 2026, triggering the first application of the new Australian Standard on Sustainability Assurance — ASSA 5000. For Australian businesses navigating this landscape, understanding what the regime requires, how assurance is phased, and what to look for in a qualified auditor has never been more important.

Understanding Mandatory Climate Reporting and Assurance in Australia

Australia's mandatory climate reporting framework is established under the Corporations Act 2001, as amended by the Treasury Laws Amendment (Financial Market Infrastructure and Other Measures) Act 2024. Entities are required to prepare a sustainability report — including climate-related financial disclosures aligned with AASB S2 — as part of their annual reporting obligations.

The framework is phased across three groups based on entity size, with Group 1 entities (the largest) subject to reporting obligations first. Assurance of the sustainability report is mandatory and is governed by standards issued by the Auditing and Assurance Standards Board (AUASB).

The Three Reporting Groups

• Group 1: Large listed entities and large unlisted entities meeting two of three size thresholds (500+ employees, $1 billion+ consolidated gross assets, $500 million+ consolidated revenue) — reporting commenced for financial years beginning on or after 1 January 2025
• Group 2: Mid-sized entities meeting two of three lower thresholds (250+ employees, $500 million+ gross assets, $200 million+ revenue) — reporting commences for financial years beginning on or after 1 July 2026
• Group 3: Smaller entities meeting two of three further thresholds — reporting commences for financial years beginning on or after 1 July 2027

ASSA 5000: The New Sustainability Assurance Standard

The AUASB adopted the international standard ISSA 5000 as the Australian standard for sustainability assurance, titled ASSA 5000 — General Requirements for Sustainability Assurance Engagements. This standard applies to both mandatory and voluntary sustainability assurance engagements and sets out the fundamental requirements for practitioners conducting these engagements.

ASSA 5000 is a comprehensive, principles-based standard that draws on the existing framework of Australian Auditing Standards while addressing the unique characteristics of sustainability information — including its forward-looking nature, the use of estimates and scenarios, and the diversity of data sources involved.

Key Features of ASSA 5000

• Prohibition on direct assistance: ASSA 5000 prohibits the use of direct assistance by internal auditors in sustainability assurance engagements, aligning with existing prohibitions for financial report audits in Australia
• Competence requirements: Practitioners must have competence in both assurance methodology and the subject matter of the sustainability report — including climate science, emissions accounting, and the AASB S2 disclosure requirements
• Evidence standards: The standard requires practitioners to obtain sufficient appropriate evidence to support their assurance conclusion, with particular attention to the reliability of data, the reasonableness of estimates, and the completeness of disclosures
• Independence: Practitioners must comply with the independence requirements of APES 110 — Code of Ethics for Professional Accountants — as applied to assurance engagements

ASSA 5010: The Phased Assurance Timeline

ASSA 5010 governs the specific timeline and phasing for assurance of climate-related information required under the Corporations Act. The standard distinguishes between limited assurance and reasonable assurance, with the level of assurance required escalating over time.

• Limited assurance (initial phase): Group 1 entities are subject to limited assurance for their first sustainability reports. Limited assurance provides a lower level of confidence than reasonable assurance and involves primarily inquiry and analytical procedures
• Reasonable assurance (full audit): From 1 July 2030, reasonable assurance — equivalent to a full audit — becomes mandatory for all climate disclosures across all groups. This is a significantly more rigorous standard, requiring the auditor to obtain sufficient evidence to express a positive opinion
• Transition period: The phased approach is designed to give entities and their auditors time to build the systems, data infrastructure, and expertise required to support reasonable assurance

ASIC's Early Observations and Enforcement Posture

The Australian Securities and Investments Commission (ASIC) is actively monitoring the first wave of sustainability reports lodged by Group 1 entities. In May 2026, ASIC published early observations to guide entities preparing for the 30 June 2026 reporting season — and the observations contain important warnings for both preparers and their auditors.

ASIC has cautioned against the use of disclaimers that conflict with the statutory framework of the Corporations Act, noting that such disclaimers may themselves be misleading. The Commission has also flagged concerns about the quality of cross-referencing to AASB S2 requirements and the clarity of judgements and assumptions disclosed in sustainability reports.

ASIC's Key Observations for Auditors

• Disclaimer risk: Auditors should advise clients that statutory disclaimers purporting to limit the legal effect of the sustainability report may be ineffective and potentially misleading
• Disclosure quality: Auditors should assess whether judgements and assumptions are disclosed clearly and proximately — not buried in appendices or cross-referenced in ways that obscure material information
• Voluntary information: Where entities include additional voluntary climate information beyond the statutory requirements, auditors should assess whether this information obscures or contradicts the mandatory disclosures
• Cross-referencing: ASIC has noted that cross-referencing to other documents must meet the strict requirements of AASB S2 — auditors should verify that all cross-references are compliant

Australian Regulatory Context

The mandatory climate reporting and assurance regime is administered by ASIC under the Corporations Act. ASIC has broad powers to investigate and take enforcement action in relation to sustainability reports, including the power to issue infringement notices, seek civil penalties, and apply for injunctions.

The AUASB is responsible for issuing and maintaining the assurance standards — ASSA 5000 and ASSA 5010 — and provides implementation support and guidance for practitioners. The AUASB has indicated that it will continue to monitor the application of the standards and issue further guidance as the regime matures.

Auditors of sustainability reports must be Registered Company Auditors (RCAs) under the Corporations Act. While the same auditor may conduct both the financial report audit and the sustainability report assurance engagement, this is not strictly required for all entities. Auditors should assess independence implications carefully where they provide both services.

The government has also signalled potential reforms to reduce the reporting burden for smaller entities, including raising monetary thresholds for large proprietary companies and refining assurance settings. ASIC has indicated it will participate in the consultation process for these proposed reforms — businesses and their auditors should monitor developments closely.

Questions to Ask Your Auditor

As mandatory climate reporting and assurance obligations expand to Group 2 and Group 3 entities, the following questions will help you assess whether your auditor has the expertise and systems to support your compliance.

1. Are you a Registered Company Auditor with demonstrated competence in sustainability assurance under ASSA 5000?
2. What experience does your firm have in assuring climate-related disclosures aligned with AASB S2?
3. How will you assess the reliability of our emissions data, scenario analysis, and climate-related estimates?
4. What is your approach to assessing the completeness and accuracy of our AASB S2 cross-references?
5. How will you manage independence requirements if you are also conducting our financial report audit?
6. What steps are you taking to prepare for the transition from limited to reasonable assurance by 1 July 2030?
7. How will you keep us informed of ASIC observations and AUASB guidance as the regime evolves?

How MyMoney® Can Help

Mandatory climate reporting assurance is a new and technically demanding discipline. Not all auditors have the competence, systems, or experience to conduct ASSA 5000 engagements to the standard that ASIC and the AUASB expect. Choosing the wrong auditor can expose your business to regulatory risk, reputational damage, and the cost of remediation.

MyMoney® connects Australian businesses with qualified auditors who have demonstrated expertise in sustainability assurance, AASB S2 compliance, and the evolving requirements of the mandatory climate reporting regime. Whether you are a Group 1 entity already subject to assurance obligations or a Group 2 entity preparing for the 1 July 2026 commencement, the right auditor can give you confidence in your disclosures.

Post a Brief to describe your sustainability assurance needs and receive tailored proposals from experienced auditors. Or Browse Auditors on the MyMoney® Marketplace to compare qualifications, experience, and client reviews today.