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

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

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:

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

💡 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.