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
We’ve worked with companies undergoing limited and reasonable assurance — and we bring that know-how to every client engagement.
FAQs
What assurance does SB 253 require for emissions reporting and when does it begin?
SB 253 mandates third‑party assurance for emissions disclosures. Companies must obtain limited assurance for Scope 1 and Scope 2 emissions starting in 2026. Limited assurance for Scope 3 begins in 2030, and reasonable assurance for Scope 1 and 2 becomes mandatory in 2030.
What is the difference between limited assurance and reasonable assurance under SB 253?
Limited assurance involves a plausibility check—verifying that nothing suggests the reported emissions data is materially incorrect. Reasonable assurance is a deeper level of scrutiny, including testing of controls, methodologies, and data to confirm accuracy.
Who qualifies to provide third‑party assurance under SB 253?
Assurance providers must be independent of the reporting entity, technically competent in greenhouse‑gas accounting, experienced in environmental or sustainability assurance, and follow recognized professional standards. CARB will define further provider qualifications by January 2025.
Which assurance frameworks are acceptable for SB 253 verification?
Commonly accepted assurance frameworks include ISAE 3000, CSAE 3410, AA1000AS, and ISO 14064‑3 / ISO 14065. Companies must disclose which framework their assurance provider uses.
What kind of documentation and data systems are needed to meet SB 253 assurance requirements?
Companies must maintain traceable data sources (e.g., invoices, meter readings), document methodologies aligned with the GHG Protocol, retain version-controlled audit trails, and conduct internal reviews to simulate external assurance audits.
What triggers the escalation from limited to reasonable assurance under SB 253?
The escalation occurs in 2030, when reasonable assurance becomes mandatory for Scope 1 and Scope 2 emissions. Scope 3 emissions move from optional assurance to requiring limited assurance.
Why is assurance under SB 253 more demanding than other jurisdictions?
SB 253 places climate disclosures on par with financial audits, requiring robust traceability and audit‑ready systems well in advance of 2030. Unlike traditional sustainability reporting, climate reporting under SB 253 must support high‑assurance verification processes.
