Assurance of Emissions What limited vs. reasonable assurance really changes.

As climate disclosure rules tighten, the assurance of emissions data is moving from a voluntary exercise to a regulatory requirement. Yet many companies and investors are still unclear about the difference between limited assurance and reasonable assurance, and why the distinction matters. Limited assurance—the more common starting point—provides a lower level of scrutiny. In this approach, an independent auditor or assurance provider primarily conducts inquiries, analytical reviews, and sample testing to check whether anything has come to their attention that would indicate the emissions data is materially misstated. The resulting conclusion is phrased in cautious terms, such as: “Nothing has come to our attention that causes us to believe the data is not fairly presented.” This gives stakeholders some comfort that obvious errors have been ruled out, but it stops short of confirming accuracy with high confidence.

Reasonable assurance, by contrast, is far more rigorous and is equivalent to the level of assurance typically provided in a financial audit. It requires detailed evidence testing, verification of source data, controls walkthroughs, and often site-level checks to confirm that emissions have been calculated in line with the GHG Protocol or other standards. The conclusion is expressed more strongly, stating that the auditor believes the data “is, in all material respects, fairly presented.” This higher bar gives investors, regulators, and other stakeholders greater confidence in the reliability of reported emissions—but it also requires stronger internal controls, comprehensive data trails, and greater readiness from the reporting company.

The shift from limited to reasonable assurance has real-world consequences. Companies may need to upgrade data collection systems, integrate sustainability data into enterprise risk and finance systems, and improve governance to ensure emissions numbers are audit-ready. The cost of assurance also rises, since auditors spend more time testing controls and verifying records. Yet the benefits are significant: reasonable assurance reduces the risk of restatements, bolsters credibility with investors, and helps companies prepare for stricter rules such as the EU’s CSRD or California’s climate disclosure laws, which expect higher levels of verification over time.

Ultimately, the distinction is not just about audit terminology—it’s about confidence and accountability. Limited assurance tells stakeholders that the data has been reviewed at a surface level; reasonable assurance signals that it has been tested with the same rigor as financial accounts. As climate data becomes financially material, the market is moving quickly toward expecting the latter. For companies, the key question is no longer whether to pursue assurance, but when and how to raise the level to meet the expectations of regulators, investors, and the public.