Limited vs reasonable assurance on emissions data: what is the difference and which do I need?

Question

Senseible · Accepted Answer

Limited assurance means the assurer found nothing suggesting your emissions are materially wrong. Reasonable assurance is a positive opinion that they are fairly stated, backed by far more testing. You need whichever your regulator, lender or buyer names: CSRD asks for limited, SEBI's BRSR Core asks large listed companies for reasonable assurance or an assessment. Limited assurance is written in the negative: nothing has come to the assurer's attention that causes them to believe the statement is not prepared, in all material respects, in line with the stated criteria. Reasonable assurance is written in the positive: in the assurer's opinion, the statement is prepared, in all material respects, in line with the criteria. Both are defined in ISAE 3410 for greenhouse gas statements and in the newer ISSA 5000 for sustainability information generally. Neither is absolute; both work to a materiality threshold. Limited assurance leans on enquiry and analytical review: the assurer asks how figures were built, compares them with prior years and production, and checks a sample. Reasonable assurance adds deeper testing: understanding and often testing controls, larger samples traced back to invoices and meter readings, recalculating factors, and site visits where emissions are material. In practice reasonable assurance takes longer, costs more, and fails faster when source documents are missing. A gap that limited assurance notes as an observation can stop a reasonable assurance opinion. SEBI BRSR Core: the July 2023 circular set reasonable assurance for the largest listed companies, phased by market capitalisation from the top 150 in FY 2023-24 to the top 1,000 in FY 2026-27. A March 2025 circular allowed a third-party assessment as an alternative. EU CSRD: limited assurance of the sustainability statement. The 2026 simplification removed the earlier plan to move to reasonable assurance. Green loans and buyer programmes: set by the contract. Many accept limited assurance or a verification statement; read the facility terms. Voluntary reports with no rule: limited assurance is the usual first step. If a regulator names the level, use that level and the standard it names. If a lender or buyer asks, get their requirement in writing before engaging an assurer. If nobody asks, start with limited assurance on Scope 1 and 2, fix what the assurer finds, and move to reasonable only when someone relies on the number for money or a public claim. Whichever level you choose, assume every figure will be traced to a source document.