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Glossary/Engagements and reports

ESG assurance

ESG assurance is independent examination or review of environmental, social and governance information, such as greenhouse gas emissions, using suitable criteria under attestation standards or international sustainability assurance standards.

CORAA TeamUpdated November 5, 2026

Definition

ESG assurance is a practitioner's report on sustainability information. In the United States, CPAs perform it under the AICPA attestation standards, using AT-C 105 with AT-C 205 for an examination or AT-C 210 for a review. The AICPA's guide on attestation engagements on sustainability information, last updated in December 2022, is the practice reference. The AICPA's Auditing Standards Board has exposed proposed sustainability-specific sections, AT-C 325 for examinations and AT-C 330 for reviews, that build on IAASB's ISSA 5000.

Why it matters in an audit or review

Lenders, customers and regulators in other jurisdictions ask for assurance on emissions and other metrics. The practitioner needs suitable criteria, subject matter specialists where required, and a materiality level set for the subject matter, not borrowed from the financial statements.

Example

Illustrative: a company reports 586 metric tons of CO2e. A reviewer tests the activity data, such as electricity invoices, and the factors used. The assurance level, limited or reasonable, is stated in the report.

Common mistakes

  • Applying financial statement materiality to emissions data.
  • Starting without documented boundaries, base year and factors.

Sources

Definitions paraphrase AICPA and FASB guidance; read the standard itself before relying on a requirement. Example figures are illustrative. This page is guidance, not professional advice. Report an error

Standards

AT-C 105AT-C 205AT-C 210ISSA 5000

Related terms

  • ISSA 5000
    ISSA 5000 is the IAASB's global standard for assurance engagements on sustainability information, applying to limited or reasonable assurance and effective for periods beginning on or after December 15, 2026.
  • Suitable criteria
    Suitable criteria are benchmarks used to measure or evaluate subject matter in an attestation engagement, with characteristics of relevance, objectivity, measurability and completeness, and available to intended users.
  • Limited assurance
    Limited assurance is a level of assurance lower than reasonable assurance, provided in attestation review engagements, where the practitioner reports a conclusion that nothing came to attention indicating a material misstatement.
  • Reasonable assurance
    Reasonable assurance is a high but not absolute level of assurance, provided in audits and attestation examinations, expressed as an opinion that subject matter is free of material misstatement.
  • Attestation engagement
    An attestation engagement is one in which a practitioner issues a report on subject matter, or on a responsible party's assertion about it, measured against suitable criteria, as an examination, review or agreed-upon procedures engagement.

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