What are the assurance requirements under SB 253?

SB 253 requires independent third-party assurance for greenhouse gas emissions disclosures. Companies must obtain limited assurance for Scope 1 and Scope 2 emissions starting in 2026, with more stringent assurance requirements introduced over time.

When does limited assurance begin under SB 253?

Limited assurance begins in 2026 for Scope 1 and Scope 2 emissions disclosures based on FY 2025 data. This is the first phase of mandatory third-party verification under California’s climate disclosure law.

When does reasonable assurance become mandatory?

Reasonable assurance becomes mandatory from 2030 onward for Scope 1 and Scope 2 emissions. Scope 3 disclosures begin moving into limited assurance requirements from 2030 as well.

What is the difference between limited and reasonable assurance?

Limited assurance is a plausibility-level review where the verifier checks whether anything suggests the reported data is materially incorrect. Reasonable assurance is a deeper audit-like process involving testing of controls, source data, calculations, assumptions, and methodologies.

What documentation is needed for SB 253 assurance?

Companies need traceable source data such as utility bills, fuel logs, supplier records, emissions factors, methodology documentation, version control history, and evidence trails linking each reported number back to its source.

How should companies prepare for SB 253 assurance requirements?

Companies should begin by centralizing emissions data, documenting calculation methodologies, establishing internal controls, running mock audits, and engaging assurance providers early to ensure readiness for the 2026 deadline.

Third-Party Assurance for SB 253: What’s Required?

Q: Who can provide assurance under SB 253?

Assurance must be provided by an independent and technically competent third-party verifier with expertise in greenhouse gas accounting and recognized assurance frameworks such as ISAE 3000, ISO 14064-3, or equivalent standards.

3 min. read
Anviksha Mishra

SB 253 assurance requirement for Scope 1, 2, 3 emissions with timelines and provider criteria

SB 253 is not just about reporting emissions — it’s about proving they’re real. Starting in 2026, large companies must submit third-party assured GHG disclosures for Scope 1 and 2 emissions. By 2030, limited assurance will also extend to Scope 3.

This post breaks down:

What third-party assurance means under SB 253
Who qualifies as an assurance provider
Timelines and escalating assurance levels
How this intersects with CSRD, SEC, and ISO standards
What to do now to avoid scrambling later

Why Third-Party Assurance Matters

In California’s eyes, emissions disclosures are financial-grade data. Just like a company can’t publish unaudited financials, it now can’t submit unverified emissions data.

Third-party assurance ensures:

Accuracy: Your data actually reflects your footprint
Credibility: Stakeholders trust what you report
Audit trail: There’s documentation for every figure you publish

Under California’s SB 253 assurance requirement, third-party limited assurance for Scope 1 and Scope 2 emissions becomes mandatory in 2026, with reasonable assurance and Scope 3 requirements phased in by 2030.

What SB 253 Requires — Scope by Scope

Emission Scope	Required in Report	Third-Party Assurance Required?
Scope 1	Yes	Yes (from 2026 onward)
Scope 2	Yes	Yes (from 2026 onward)
Scope 3	Yes	Voluntary until 2030, then required

Note: Scope 3 includes upstream and downstream value chain emissions — typically 70-90% of a company’s total footprint.

Assurance Timelines for Scope 1, 2, and 3

Year	Scope 1 & 2	Scope 3
2026	Limited assurance required	Not required
2027-2029	Limited assurance	Still optional
2030 onward	Reasonable assurance required	Limited assurance begins

Limited vs. Reasonable:

Limited assurance = “Nothing indicates this is wrong”
Reasonable assurance = “We’ve tested and confirmed it’s right”

This is a major ramp-up in scrutiny — most firms today are only equipped for limited.

Who Can Provide Assurance Under SB 253?

SB 253 requires the assurance provider to be:

Independent from the reporting entity
Technically competent in GHG accounting
Experienced in environmental or sustainability assurance
Following recognized assurance standards

Approved providers include:

Public accounting firms with ESG practices
Climate consultancies with qualified audit teams
Verification bodies accredited under ISO 14065

CARB will define more detailed provider qualifications by January 2025.

Assurance Frameworks: ISAE 3000, CSAE 3410, and More

Commonly accepted assurance standards:

Framework	Region	Focus
ISAE 3000	Global	General non-financial assurance
CSAE 3410	Canada	Assurance of GHG statements
AA1000AS	Global	Sustainability and ethics-focused
ISO 14064-3 / 14065	Global	Verification of GHG emissions

SB 253 doesn’t mandate a single framework — but your provider must disclose the one used and align with professional norms.

Preparing for Limited and Reasonable Assurance

Here’s what makes your emissions reporting “assurable”:

1. Traceable data

Every Scope 1 or 2 data point should link back to a meter reading, invoice, or log file.

2. Documented methodology

Your calculation methods must align with the GHG Protocol, including emission factors used, boundaries, and assumptions.

3. Version control and audit trail

You need evidence of:

Data origin
Any modifications
Who made changes and why

4. Internal review

Conduct a dry run — simulate what an external reviewer will see. Clean data now saves pain later.

Key Differences From Other Jurisdictions

Requirement	SB 253	CSRD (EU)	SEC (US, proposed)
Scope 1 & 2 assurance	Required (2026)	Required (2025–26)	Proposed (phase-in)
Scope 3 assurance	Required (2030)	Optional (2026+), encouraged	Not yet required
Standard	GHG Protocol, flexible on framework	ESRS + limited assurance	GHG Protocol
Frequency	Annual	Annual	Annual

💡 If you’re already preparing for CSRD, your assurance workflows will carry over — with some adaptation.

How Sprih Supports Assurance-Ready Reporting

Sprih’s platform was designed with audit-readiness in mind. Here’s what we offer:

Source traceability — every emissions value links to its origin (energy bills, telemetry, ERP exports)
Standardized calculations — aligned with GHG Protocol and major assurance frameworks
User-level activity logs — version control for internal QA and third-party review
Multi-format exports — ready for SB 253, CSRD, SEC, and voluntary frameworks
Assurance collaboration tools — scoped data access, comment threads, validation logs

We’ve worked with companies undergoing limited and reasonable assurance — and we bring that know-how to every client engagement.