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
SB 253 makes this assurance mandatory — not optional — for Scope 1 and 2 starting in 2026.
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 is the difference between limited and reasonable assurance?
Limited assurance provides a basic review to confirm that nothing appears materially misstated. Reasonable assurance involves more rigorous data testing, validation, and confirmation that your emissions disclosures are accurate and complete. SB 253 moves from limited to reasonable by 2030.
Who decides if our provider is eligible?
CARB (California Air Resources Board) will issue formal eligibility criteria by January 1, 2025. Until then, assurance providers must meet general standards of independence, technical expertise in GHG accounting, and adherence to professional assurance frameworks.
Does SB 253 require Scope 3 assurance today?
No. Scope 3 assurance is voluntary until 2030. However, starting that year, limited assurance will be required. Early preparation is recommended—especially for high-emission categories like purchased goods, logistics, and product use.
Can I use the same firm for financial audit and GHG assurance?
Yes, as long as the emissions assurance team is functionally independent from your financial audit team. The firm must also meet SB 253’s standards for technical competency and environmental assurance practices.