ISSA 5000 Is Coming: Is Your ESG Information Ready to Stand Up to Scrutiny?

The next challenge in ESG reporting may not be disclosure — but evidence.

The International Auditing and Assurance Standards Board (IAASB)’s International Standard on Sustainability Assurance (ISSA) 5000 is set to become effective for sustainability assurance engagements for periods beginning on or after 15 December 2026. The new standard establishes a global baseline for sustainability assurance and is already being adopted or considered across jurisdictions. In Hong Kong, a local equivalent, HKSSA 5000, has been issued, while Singapore is among the jurisdictions currently progressing adoption.

For companies, however, the significance of ISSA 5000 goes beyond the assurance engagement itself.

It raises a more fundamental question:

If someone were to challenge a number or statement in your ESG report, could you demonstrate exactly how you arrived at it?

The report is only the tip of the iceberg

An ESG report may present a relatively simple figure, total greenhouse gas emissions, energy consumption, employee turnover or progress against a sustainability target.

But behind that figure could be hundreds of data points, spreadsheets, invoices, conversion factors, assumptions, estimates and management decisions.

In our experience, the difficulty is often not calculating the final number. It is establishing whether the evidence behind the number is complete, consistent and traceable.

For example:

• Can the reported figure be traced back to its original source?
• Is the calculation methodology clearly documented?
• Are assumptions and estimation methods recorded?
• Has the reporting boundary been applied consistently?
• Can different teams reproduce the same result?
• Has the information been appropriately reviewed before disclosure?

These questions become increasingly important as sustainability information moves closer to the discipline traditionally associated with financial reporting.

Think “evidence chain”, not just “data collection”

A robust ESG reporting process should create a clear chain:

Source data → Methodology → Calculation → Review → Approval → Disclosure

This is particularly relevant for greenhouse gas emissions, where data may come from multiple facilities, utility bills, suppliers and estimation methods. But the principle applies equally to qualitative disclosures, including climate risks, governance arrangements, targets and transition plans.

A credible disclosure is therefore not simply one that looks reasonable.

It is one for which the company can explain why it is reasonable.

What should companies do now?

ISSA 5000 does not mean that every company needs to build an audit system overnight. Nor should companies wait until an assurance provider arrives before thinking about data quality.

A more practical approach is to start strengthening the evidence chain now:

Assign clear ownership. Document methodologies. Retain supporting records. Review calculations. Record key assumptions. Maintain consistency in boundaries and definitions.

Most importantly, ESG data should not be treated as information collected only when the annual report is due.

The companies that will be better prepared for the next phase of ESG reporting are not necessarily those with the most sophisticated reporting systems. They are the ones that understand where their information comes from, who is responsible for it and what evidence supports it.

As ISSA 5000 moves towards implementation, the question for companies is no longer simply: “Have we disclosed it?”

It is increasingly: “Can we support it?”

That may be the real test of a credible ESG report.

At GreenCo, we help companies prepare for this next stage of ESG reporting, from strengthening ESG data and documentation, to preparing sustainability disclosures and assessing their readiness for assurance. We also provide independent sustainability assurance services, helping companies obtain greater confidence in the reliability and credibility of their reported sustainability information.

Whether you are preparing for your first assurance engagement or looking to strengthen your existing ESG reporting processes, contact GreenCo today to discuss how we can help you build a more robust and assurance-ready ESG reporting process.

GreenCo is a professional ESG advisory firm accredited with ISO 9001 in the Provision of ESG / Sustainability Reporting, Sustainanbility and Climate Disclosures and GHG Accounting Advisory Services. Established in 2016, we were born to tackle ESG and climate risk management challenges. GreenCo has a professional team consists of talents with multiple backgrounds with

• PhD
• Practitioner Member of the Institute of Sustainability and Environmental Professionals (ISEP)
• CFA (the CFA Institute) and Certificate in ESG Investing
• EFFAS Certified ESG Analyst (CESGA)
• GRI Certified Sustainability Professional
• Certified Public Accountant (for assurance in accordance with ISAE 3000)
• Member of Global Association of Risk Professionals
• Master’s degree in envirnomental science

GreenCo has solid track record in ESG advisory for over 80 listed companies in Hong Kong, Mainland China, Singapore and Korea, covering all industries under the Hang Seng Industry Classification System.