NZ Electricity-Sector GHG Assurance Audit 2026

Each cell shows the level of independent assurance obtained over the issuer’s FY2025 disclosure for that scope. Green is reasonable; amber is limited; grey is unassured or not disclosed.

Reasonable assurance is audit-statement-level confidence (“in our opinion”). Limited assurance is lower-confidence, negative-form (“nothing has come to our attention”). Under NZ SAE 1, reasonable assurance is expected to become the ceiling for Scope 1 and 2 over time.

1. All four listed gentailers obtain independent third-party assurance over their FY2025 greenhouse-gas emissions disclosures. 100% assurance coverage of the sector.
2. The Big 4 split is even.Each of Deloitte, EY and KPMG signs one gentailer; EY signs a second as the Auditor-General’s appointee. No non-Big-4 provider is engaged.
3. 2 of 4 appointments are made by the Auditor-General (Genesis and Mercury) reflecting the mixed-ownership-model status of both issuers. The remaining two (Contact, Meridian) appoint their assurance provider directly.
4. The assurance level gap on Scope 1 & 2 is the single most visible comparability dimension. 2 of 4issuers (Genesis and Meridian) hold reasonable assurance on Scope 1 and 2. Mercury holds limited assurance across all three scopes. Contact’s assurance covers a broader GRI perimeter at limited level and does not separately uplift Scope 1 & 2.
5. Scope 3 is universally at limited assurance where it is assured at all. Mercury is the only issuer whose assured scope explicitly names Scope 3 at the limited level; Contact does not estimate Scope 3 for FY25.
6. Standards cited vary. All four issuers reference ISAE 3410 or its NZ-adopted equivalent; three (GNE, MCY, MEL) explicitly reference NZ SAE 1 or NZ SA 1 as NZ SAE 1 phases in. This naming will converge over the next one to two reporting cycles as NZ SAE 1 becomes the default.
7. Two key matters appear repeatedly in the assurance opinions: the spend-based method used for purchased goods and capital goods in Scope 3 (inherent uncertainty), and the calculation basis for geothermal emissions (internally calculated unique emission factors). Neither results in a qualified opinion but both are disclosed as matters warranting user attention.

Each of the four listed gentailers retains a separate assurance provider. The Big 4 collectively hold 100% of the sector.

Every issuer cites a primary assurance standard in its assurance report. The exact mix of standards differs, reflecting the ongoing transition to NZ SAE 1 as the default for GHG engagements.

Two axes distinguish assurance engagements: the level (limited vs reasonable) and the scope(which disclosures sit inside the assured perimeter). The level gap on Scope 1 & 2 is the single most visible comparability dimension across the sector.

No issuer in the sector received a qualified, adverse, or disclaimer-of-opinion assurance report for FY25. Two themes recur across the matters-of-emphasis disclosed.

Every finding in this report is extracted directly from each issuer’s FY2025 climate-related disclosures / climate statement. Page numbers refer to PDF pages of the source document. No figure is paraphrased where the source is quotable.

• CEN
  CEN — CEN Climate-related Disclosures / Integrated Report FY2025(138 pp · 1 July 2024 – 30 June 2025)
• MEL
  MEL — MEL Climate-related Disclosures FY2025(54 pp · 1 July 2024 – 30 June 2025 (Year 7 of climate reporting))
• GNE
  GNE — GNE Climate-related Disclosures FY2025(79 pp · 1 July 2024 – 30 June 2025)
• MCY
  MCY — MCY Climate Statement FY2025(30 pp · 1 July 2024 – 30 June 2025)

Companion page with full methodology comparison (including non-assurance fields): NZ Gentailer Climate-Disclosure Methodology Comparison. Extraction date: 2026-04-20.

• Treat limited and reasonable assurance as materially different reliance levels. A reasonable-assurance Scope 1 figure can be relied on at the same level as an audited financial number. A limited-assurance figure cannot.
• Ask what is inside the assured perimeter, not just the level.Contact’s limited assurance covers a broader GRI perimeter, not specifically Scope 1 and 2 metrics. The scope statement in the assurance report is load-bearing.
• Expect Scope 3 restatements over the next two reporting cycles. As other CREs complete the materiality assessments Mercury completed in FY25, restatements of prior years will continue. Year-over-year comparisons that span a restatement require re-baselining.
• Watch the key-matters language.Recurring themes across the sector (spend-based Scope 3; geothermal emission factors) are not issuer-specific concerns — they are sector-wide methodology fragilities that NZ SAE 1 will not resolve on its own.

The assurance market for NZ gentailer GHG disclosures is effectively formed. Big 4 have 100% share; appointment paths split evenly between direct and Auditor-General. What remains open is the shape of what NZ SAE 1 requires as it phases in. Three propositions, in order of materiality:

1. Reasonable assurance on Scope 1 and 2 should become the default for CREs within one to two reporting cycles. Half the gentailer sector is already there. A named transition date removes ambiguity and prevents the issuer-by-issuer divergence this report documents from becoming permanent.
2. Scope 3 assurance expectations need to be standardised by category, not in aggregate.Limited assurance on “Scope 3 gross emissions” means very different things when Scope 3 is 0 categories vs 9 categories. A category-level assurance scope disclosure would surface this today without waiting for NZ SAE 1 amendments.
3. The recurring key matters should be elevated to standard-level guidance, not left to preparer discretion.Spend-based Scope 3 uncertainty and internally-calculated geothermal emission factors are not exceptions; they are the sector’s baseline. Named guidance on both would move the conversation from “is this acceptable?” to “is this being applied consistently?”