1. The Progression from Limited to Reasonable Assurance
To prevent “greenwashing”—the practice of publishing misleading environmental claims—regulators have added mandatory external audit requirements for sustainability reports.
- Limited Assurance: A lower level of assurance, typically characterized by a negative conclusion (“nothing has come to our attention to indicate that the data is materially misstated”). The procedures focus heavily on inquiries and analytical comparisons.
- Reasonable Assurance: A high level of assurance equivalent to a traditional financial statement audit. The procedures include rigorous internal control testing, sample verification, and detailed walk-throughs of primary emission source data.
2. Assurance Standards Frameworks
Sustainability assurance engagements are conducted by certified auditors using standardized verification protocols, such as ISAE 3000 (Assurance Engagements Other than Audits or Reviews of Historical Financial Information) and ISAE 3410 (Assurance Engagements on Greenhouse Gas Statements)