ISAE 3410 — Withdrawn in December, and What Replaces It
If you commission assurance over a greenhouse gas statement, the standard named in your engagement letter is almost certainly ISAE 3410. In three and a half months it will not exist. The IAASB approved its withdrawal in March 2025, announced it in May, and it takes effect on 15 December 2026.
What replaces it is not a greenhouse gas standard. ISSA 5000 is a general standard for assurance over all sustainability information, of which greenhouse gas data is one kind. The IAASB’s reasoning was straightforward: GHG emissions are sustainability information, ISSA 5000 is comprehensive enough to cover assurance over them, and a separate GHG standard is therefore redundant.
Between those two facts sits a transition window that has been widely misread, and two narrow routes by which a local version of ISAE 3410 survives — neither of which lets a practitioner claim compliance with IAASB standards. This page sets out all three.
1. Is ISAE 3410 still in force?
Today, yes. From 15 December 2026, no.
ISAE 3410 remains a live IAASB standard until that date. What changes then is not that it becomes optional or discouraged — it is withdrawn, which means the IAASB no longer maintains or issues it, and it ceases to be available for assurance engagements performed under IAASB standards.
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2. The withdrawal, dated
3. Which standard governs your engagement
The answer depends on the reporting period, not on the date you sign the engagement letter — which is the source of most of the confusion about this transition.
4. The transition window nobody has answered
ISSA 5000’s applicability is defined by the reporting period, and that produces a gap most commentary has skipped over.
The first engagements squarely inside ISSA 5000 are those on periods beginning on or after 15 December 2026 — which, for a calendar-year reporter, means FY2027, assured in 2028. That is later than most planning assumptions treat it.
5. The two ways ISAE 3410 survives, and what they cost
The IAASB’s staff FAQ of August 2025 sets out two circumstances in which the pre-ISSA-5000 standards remain available. Both are real, both are narrow, and both carry the same price.
An assurance report is bought for the sentence that says what it was performed under. If your provider works to a surviving local standard, the engagement is perfectly legitimate — but the report cannot say it complied with IAASB standards, and a reader who expects that phrase will notice its absence. Where an assurance statement is being relied on across borders, or fed into a disclosure that references international standards, that difference is the whole point of the exercise.
6. What ISAE 3410 actually required
For as long as it applies, ISAE 3410 remains a demanding standard, and it is worth restating what it puts on the practitioner — not least because ISSA 5000 was built on it rather than in place of it. The IAASB described its approach as “no greenfielding”: the new standard builds on established practice in ISAE 3000 and ISAE 3410 rather than starting over.
| The engagement requires | What that means in practice |
|---|---|
| An understanding of the entity and its GHG statement | Including how emissions arise, the boundary drawn, and the quantification method used. |
| Risk assessment | Identifying where the statement is most likely to be materially misstated, which in practice means the estimation-heavy items. |
| Consideration of internal control | How the entity captures activity data, and whether those controls are capable of producing a reliable figure. |
| Evidence over quantification | Emission factors, activity data, and the arithmetic joining them. |
| A conclusion at a stated level | Limited or reasonable, expressed in the form the standard prescribes. |
Neither ISAE 3410 nor ISO 14064-3 imposes a factor-provenance test on the assurer. Nothing requires your practitioner to establish that each emission factor you used came from the edition you say it did. The duty to name and retain the factors behind your numbers sits with you, and a clean assurance opinion is not a statement about where those factors came from. Our Assurance Readiness Checker exists for exactly that gap.
7. Limited and reasonable assurance
Both ISAE 3410 and ISSA 5000 provide for two levels, and the distinction is frequently understated in the reporting that follows.
| Limited assurance | Reasonable assurance | |
|---|---|---|
| The conclusion | Negative form — nothing has come to the practitioner’s attention suggesting a material misstatement | Positive form — the statement is prepared, in all material respects, in accordance with the criteria |
| Level of assurance | Substantially lower | High, though never absolute |
| Procedures | Differ in nature, timing and extent — typically enquiry and analytical procedures | More extensive, including tests of detail and often of controls |
| What most GHG statements get | This one | Rare outside regulated regimes |
The practical consequence: the overwhelming majority of assured greenhouse gas statements carry a limited assurance conclusion, and a limited conclusion is not a statement that the number is right. It is a statement that nothing came to the practitioner’s attention to suggest it is materially wrong, on procedures substantially narrower than an audit.
8. ISAE 3410 and ISSA 5000, side by side
| ISAE 3410 | ISSA 5000 | |
|---|---|---|
| Status | Withdrawn 15 Dec 2026 | Effective 15 Dec 2026 |
| Subject matter | Greenhouse gas statements only | All sustainability information, on any topic and under any framework |
| Who may perform it | Written for professional accountants | Profession-agnostic — usable by non-accountant practitioners who meet the conditions |
| Ethical and quality regime | IESBA Code and ISQM 1 via the accountancy framework | IESBA Code and ISQM 1, applied explicitly whoever performs the engagement |
| Assurance levels | Limited and reasonable | Limited and reasonable, and combinations across subject matters |
| Materiality | Financial-statement lineage | Accommodates double materiality as applied by the entity |
| Applies by reference to | The engagement | The reporting period — which is what creates the transition window in §4 |
9. ISSA 5000 is not a greenhouse gas standard
The most common misreading of this transition is that ISAE 3410 has been replaced by an updated GHG assurance standard. It has not. ISSA 5000 is a general standard for assurance over sustainability information — climate, nature, workforce, governance, whatever a framework requires — and greenhouse gas data is one subject matter within it.
The IAASB’s reasoning was that GHG emissions are sustainability information as ISSA 5000 defines it, that ISSA 5000 is comprehensive enough to cover assurance over a GHG statement, and that a separate standard was therefore unnecessary.
That framing matters for anyone reporting under CSRD, where the assurance requirement covers the sustainability statement as a whole rather than the emissions figures alone. Under ISAE 3410 the GHG numbers needed their own standard alongside whatever governed the rest. Under ISSA 5000 they do not.
10. Who may now provide assurance
ISSA 5000 is profession-agnostic, and this is a genuine change in the market rather than a drafting nicety. It is written to be usable by professional accountants and by non-accountant assurance practitioners alike.
The door is not open unconditionally. A practitioner applying ISSA 5000 must comply with the IESBA Code — including its independence requirements — and must belong to a firm that applies ISQM 1, the quality management standard. Those two conditions do most of the work: they admit non-accountant providers while holding them to the ethical and quality infrastructure the accountancy profession already operates.
Two questions settle it. Does your firm apply ISQM 1, and are you subject to the IESBA Code including its independence provisions? A provider who cannot answer both affirmatively cannot perform an ISSA 5000 engagement, whatever technical expertise they hold. This is worth establishing before December 2026 rather than during a tender.
11. ISO 14064-3 is a different thing, and it is unaffected
This is the disambiguation most likely to save a reader from an unnecessary problem. ISO 14064-3 is not withdrawn, is not changing, and is not touched by any of the above.
| ISAE 3410 | ISO 14064-3 | |
|---|---|---|
| Issued by | IAASB, the international auditing standard-setter | ISO, the international standards organisation |
| Who applies it | Assurance practitioners, historically accountants | Validation and verification bodies |
| Status after 15 Dec 2026 | Withdrawn | Unaffected |
| Why | An IAASB decision reaches IAASB pronouncements | A different standard-setter, on its own revision cycle |
The two are routinely conflated because they do overlapping jobs and are often named in the same sentence — including on many of our own pages. They are separate instruments from separate bodies, and a withdrawal by one has no effect on the other. If your verification is performed by an accredited body to ISO 14064-3, nothing on this page changes your position.
12. What assurance does not test
Worth restating here because the transition changes none of it. An assurance engagement — under ISAE 3410, ISSA 5000 or ISO 14064-3 — tests your inventory, your boundary, your controls and your evidence to the level of assurance engaged. It does not impose a provenance test on the assurer for the emission factors you used.
That is why the factors in the MasterBrain carry their edition, publication and retrieval provenance: so that the question “which version of this factor did you use, and when” has an answer that predates the engagement rather than being reconstructed during it.
13. What to do before December 2026
- Find every engagement letter that names ISAE 3410. Anything covering a period beginning on or after 15 December 2026 names a standard that will not exist when the work is done.
- Work out which side of the line each period falls on. Period start date, not engagement date — see §3 and §4.
- Ask your jurisdiction’s standard-setter whether it has adopted ISSA 5000, and on what timetable. That answer decides whether the Q2 route is open to you.
- Ask your provider what their report will say it was performed under for your next two reporting periods. If the answer is a surviving local standard, establish now whether an IAASB compliance claim matters to your readers.
- If you are considering a non-accountant provider, confirm ISQM 1 and the IESBA Code before the tender, not after.
- Check your own published documents for references to ISAE 3410 — methodology pages, policies, prior reports. A citation that is correct today reads as an error in January.
14. Interaction with the regimes that require assurance
| Regime | What the transition changes |
|---|---|
| CSRD / ESRS | Assurance is required over the sustainability statement as a whole. A single general standard fits that shape better than a GHG-specific one bolted alongside. European assurance standards are also under development, which may supersede the international position locally. |
| IFRS S2 | IFRS S2 does not itself mandate assurance; jurisdictions adopting it decide. Where they require it, ISSA 5000 becomes the reference standard. |
| UK SECR | SECR does not require assurance. Voluntary assurance over a SECR disclosure follows the same transition as everything else. |
| California SB 253 | Requires assurance on emissions reporting. Which standard applies is a question for the regulation and the provider, and the answer moves with this transition. |
15. How GreenCalculus implements this
Assurance is where a factor’s provenance stops being a documentation nicety and becomes the thing you are asked to produce. Two of our diagnostics test the gap this page describes.
- Assurance Readiness Checker — built on the observation in §12: the assurer tests your inventory, and naming and retaining every factor is your duty, not theirs.
- Emission Factor Vintage Checker — whether the factors behind an assured statement were current for the period they were applied to.
Underneath both, every factor in the MasterBrain carries its edition, publication and retrieval provenance, and historical values remain addressable by version. Under any of these standards the question at the engagement is the same: which figure did you use, from which edition, on what date — and the useful answer is one recorded before the work started.
16. Frequently Asked Questions
Until 15 December 2026, yes. From that date it is withdrawn, taking effect alongside ISSA 5000 becoming effective. The IAASB approved the withdrawal in March 2025 and announced it in May 2025. After that date it is no longer available for assurance engagements performed under IAASB standards, subject to the two narrow routes described below.
ISSA 5000, General Requirements for Sustainability Assurance Engagements, issued by the IAASB in November 2024. It is not a greenhouse gas standard: it covers assurance over all sustainability information, of which GHG data is one subject matter. The IAASB concluded that GHG emissions are sustainability information and that ISSA 5000 was comprehensive enough to cover assurance over a GHG statement, making a separate standard unnecessary.
ISSA 5000 applies to periods beginning on or after 15 December 2026, so a calendar-2026 period beginning on 1 January 2026 falls outside it — while ISAE 3410 is withdrawn on 15 December 2026, before that engagement is performed. The IAASB’s staff FAQ does not address this window directly. In practice the answer comes from your jurisdiction’s standard-setter, which may not have adopted ISSA 5000 on the international timetable, and from your assurance provider. Ask both.
Only in two circumstances. If law or regulation in a jurisdiction requires a jurisdiction-specific version of ISAE 3410, that local equivalent can continue to be used for GHG statement assurance. And where a jurisdiction has not yet adopted ISSA 5000, practitioners there may continue to apply ISAE 3000 (Revised) until it does. In both cases the practitioner cannot claim compliance with IAASB standards unless they apply ISSA 5000.
No. ISO 14064-3 is issued by ISO, not by the IAASB, and an IAASB withdrawal reaches only IAASB pronouncements. It is unaffected by this transition and continues on its own revision cycle. The two are frequently conflated because they do overlapping jobs, but they are separate instruments from separate bodies applied by different practitioners.
Not after ISSA 5000 becomes effective. The IAASB’s staff FAQ is explicit that ISSA 5000 applies to all assurance engagements on sustainability information once effective, so ISAE 3000 (Revised) will no longer be applicable for those engagements. The exception is a jurisdiction that has not yet adopted ISSA 5000, where practitioners may continue applying ISAE 3000 (Revised) until it does — without being able to claim compliance with IAASB standards.
Yes. ISSA 5000 is profession-agnostic and is written to be used by professional accountants and non-accountant assurance practitioners alike. The conditions are that the practitioner complies with the IESBA Code, including its independence requirements, and belongs to a firm that applies ISQM 1. Establish both before engaging a provider rather than after.
Not in the way most reporters assume. Neither ISAE 3410 nor ISO 14064-3 imposes a factor-provenance test on the assurer: nothing requires your practitioner to establish that each factor came from the edition you say it did. The engagement tests your inventory, boundary, controls and evidence to the level of assurance engaged. The duty to name and retain the factors behind your numbers is yours, and a clean opinion is not a statement about where they came from.
Related References
- ISO 14064-3 — the ISO verification standard, unaffected by this transition
- ISO 14064-1 — the inventory standard the assurance is performed over
- CSRD / ESRS E1 — where assurance covers the whole sustainability statement
- IFRS S2 — disclosure, with assurance left to jurisdictions
- GHG Protocol Corporate Standard — the criteria most GHG statements are prepared against
- Assurance Readiness Checker — what the assurer tests, and what stays yours
- Emission Factor Vintage Checker — whether your factors were current for the period
