Client Alert: Latest Key Developments for SB 253 

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March 2026 updates on SB 253 reporting timelines, requirements, and Scope 3 proposals.

CARB has provided additional clarity regarding the SB 253 implementation during the March 23, 2026 workshop, building on the previously discussed November 18 updates. CARB is still seeking feedback on the proposed updates and encouraging companies to submit comments here. Below is a summary of the most important developments: 

Confirmed First-Year Reporting Requirements  

CARB reaffirmed that the first-year reporting deadline remains August 10, 2026 for Scope 1 and Scope 2 GHG emissions.  

  • Reporting requirements apply to U.S.-based entities doing business in California with >$1B revenue.  

  • The 2026 submission will not require:  

    • Use of a standardized CARB template  

    • Third-party limited assurance for Scope 1 and Scope 2 GHG emissions 

CARB also confirmed that additional guidance on the 2026 reporting intake process and extension request procedures will be available in the next couple of weeks. 

Determining the Applicable Reporting Year 

The reporting year for Scope 1 and Scope 2 GHG emissions will depend on an entity's fiscal year (FY) end:  

  • If the FY ends on or before February 1, 2026 → report FY 2025–2026 data  

  • If the FY ends after February 1, 2026 → report FY 2024–2025 data  

Reporting and Assurance Requirements in 2027 

Beginning in 2027 and beyond, CARB confirmed the following: 

  • Mandatory reporting of Scope 1, Scope 2, and Scope 3 GHG emissions annually  

  • Required third-party limited assurance for Scope 1 and Scope 2 GHG emissions 

Additionally, disclosures are expected to include the organizational boundary approach, emissions calculation methodologies and emission factors used. 

Scope 3 Reporting – Proposed Implementation Options 

CARB introduced three potential pathways for Scope 3 reporting, starting in 2027, and is seeking feedback on the following approaches. 

  • Option 1: Broad Applicability: All entities are required to report all Scope 3 categories, with flexibility to exclude those deemed de minimis provided that a clear justification is documented. 

  • Option 2: Sector-Based Phase-In: The initial focus is on high-emitting sectors (e.g., transportation, manufacturing, and energy), with expansion over time based on stakeholder feedback. 

  • Option 3: Category-Based Phase-In: The approach begins with the most commonly reported categories, Category 6 (Business Travel), Category 1 (Purchased Goods & Services), Category 3 (Fuel & Energy-related), Category 7 (Employee Commuting), and Category 5 (Waste), and expands to the remaining categories over time. This approach allows companies to voluntarily report the other 10 categories. 

CARB confirmed that multiple methodologies may be acceptable including Spend-based, Activity-based, Supplier-specific and Hybrid approaches. 

Assurance Requirements and Accepted Standards 

While third-party limited assurance is not required for 2026, CARB confirmed: 

  • Limited assurance becomes mandatory for Scope 1 and 2 starting in 2027 

  • Proposed standards include:  

    • AA1000 Assurance Standard 

    • AICPA Standards  

    • ISAE 3000 / ISAE 3410 (until December 2026) 

    • ISSA 5000 (effective December 2026) 

    • ISO 14064-3 (2019)  

As CARB continues to refine SB 253 requirements, organizations should begin preparing now to ensure timely and compliant reporting, particularly as expectations around Scope 3 disclosures, public transparency, and third-party assurance continue to evolve. Taking early action to assess data readiness, establish internal processes, and align with anticipated guidance will be critical. KERAMIDA supports clients through distinct reporting and independent assurance pathways, providing the technical expertise needed to help organizations confidently navigate and comply with SB 253 requirements.