New Zealand already requires assurance over greenhouse gas information in mandatory climate statements. In March 2026, the External Reporting Board issued ISSA (NZ) 5000 to become the new assurance standard for those disclosures and for other sustainability assurance engagements within its scope.
This is more than a future assurance concept. Climate reporting entities need to transition an operating statutory assurance process from temporary and greenhouse-gas-specific standards to the broader international baseline.
What XRB issued
ISSA (NZ) 5000 is applicable for periods beginning on or after December 15, 2026. XRB states that it is the assurance standard to use for greenhouse gas disclosures in climate statements that the Financial Markets Conduct Act requires to be assured.
For periods beginning before that date, NZ SAE 1 and ISAE (NZ) 3410 continue to apply unless the new standard is adopted early. XRB’s March announcement explains that those older standards are revoked for the new-period transition.
The related New Zealand ethics and independence requirements were also updated. Reporting teams should confirm the transition period, early-adoption decision, and applicable practitioner requirements with their provider.
The existing statutory assurance duty
The Financial Markets Authority says climate reporting entities must obtain independent assurance over the part of their climate statements relating to greenhouse gas emissions for reporting years ending on or after October 27, 2024.
That means New Zealand entities are not starting from zero. They can use findings from the first assurance cycles to strengthen readiness for ISSA (NZ) 5000, which is broader and specifically designed for sustainability information.
Our New Zealand climate disclosure guide explains the current NZ CS regime and proposed scope changes.
Plan the transition standard by standard
Create a transition memo that records:
- The reporting period and assurance standard currently used.
- The first period for ISSA (NZ) 5000 and whether early adoption is considered.
- Changes to engagement scope, terminology, evidence, reporting, ethics, and independence.
- The treatment of comparative information and prior-year methods.
- Dependencies on group or component practitioners.
Discuss whether the provider expects additional work over qualitative disclosures, estimates, forward-looking information, controls, or group components. The statutory GHG assurance perimeter remains central, but voluntary or group engagements may cover more.
Use prior findings to improve the reporting system
Classify assurance findings by root cause: incomplete source population, weak evidence, inconsistent boundary, uncontrolled factor, undocumented estimate, late review, or reporting inconsistency. Assign owners and due dates, then verify that corrective controls operate before the next close.
For greenhouse gas information, maintain a reconciled facility and source register, original data exports, calculation versions, emission-factor approvals, estimation records, and evidence of review. Link every published total back to the assured dataset.
Scope 3 can be particularly difficult because information comes from suppliers, models, and external data. Document category screening, source selection, estimation methods, exclusions, and data-quality improvements. Temporary relief in a prior year should not become a permanent process gap.
Coordinate reporting, assurance, and filing
New Zealand climate statements must be lodged on the public register, and Companies Office guidance requires details of the assurance practitioner. Build one calendar covering data cut-off, calculation, management review, assurance fieldwork, board approval, and filing.
Freeze the assured version and control subsequent edits. If a correction is required after the assurance report date, involve the practitioner and follow the applicable filing process rather than quietly changing another published copy.
Carbon Impact’s ISSA 5000 assurance-readiness solution helps New Zealand climate reporting entities connect NZ CS criteria to source data, calculations, evidence, controls, and the assurance close.
This article reflects information available on August 10, 2026 and provides general information, not assurance or legal advice.
Sources
See how Carbon Impact supports ISSA 5000 reporting — from data collection to disclosure.