Introduction

On March 23, 2026, the California Air Resources Board (CARB) held a public workshop on the regulatory development of California’s corporate greenhouse gas reporting program under Senate Bill 253. The session covered three areas: the confirmed August 10, 2026 Scope 1 and 2 reporting deadline, proposed GHG accounting and Scope 3 requirements for 2027 onward, and an early economic analysis. The 2027 framework is still in development and open for public comment until April 13, 2026. For any U.S.-based company with revenues above $1 billion doing business in California, this rulemaking will define what you must measure, disclose, and assure.

Key Takeaways

• The first SB 253 reporting deadline is confirmed: Scope 1 and 2 emissions are due August 10, 2026.
• Scope 3 reporting and assurance requirements from 2027 are still proposals under active public feedback and have not yet been finalized.
• CARB is weighing three Scope 3 implementation options, with stakeholder input due by April 13, 2026.
• Compliance costs are estimated at well under 0.02% of the $1 billion revenue threshold. The regulatory burden is manageable, but preparation time is short.

California SB 253: Who Is Covered and What the Law Requires

SB 253, the Corporate Climate Data Accountability Act, is codified under California Health and Safety Code Section 38532 and amended by SB 219. It applies to any U.S.-based entity doing business in California with annual revenues above $1 billion. This is not limited to California-headquartered companies.

Two companion laws are worth knowing:

• SB 253 ($1B threshold): mandatory GHG emissions disclosure covering Scope 1, 2, and 3.
• SB 261 ($500M threshold): mandatory climate-related financial risk disclosure.

Companies above $1 billion are subject to both. The applicability definitions and revenue thresholds were formally adopted at the February 26, 2026 Board hearing. Program fee assessments are scheduled for September 10, 2026.

California is part of a growing global movement. The March 23 workshop materials noted that jurisdictions with similar Scope 1, 2, and 3 reporting laws now represent 59% of global GDP and 66% of the global population. A joint statement from business leaders in January 2026 called full value-chain visibility essential for credible transition planning. If your company already reports under IFRS S2 or the EU CSRD, CARB has invited feedback on how those frameworks should inform California’s rules.

SB 253 Reporting Deadlines: What Is Confirmed and What Is Still Being Decided

It helps to separate what is confirmed from what is still under development.

Confirmed: 2026

• Scope 1 and 2 emissions must be reported by August 10, 2026.
• FY cutoff rule: entities with fiscal year ending on or before February 1, 2026 report FY25-26 data; those ending after report FY24-25 data.
• Standardized templates and limited assurance are not required for this first cycle.
• Guidance on extension requests is forthcoming from CARB staff.

Proposed: 2027 and Beyond

• Annual Scope 1, 2, and 3 reporting for all covered entities.
• Limited assurance for Scope 1 and 2 from an approved provider.
• Standardized reporting templates, currently in draft, to be finalized through formal rulemaking.
• Full reasonable assurance is scheduled for 2030 and falls outside the current rulemaking cycle.

These 2027 requirements are staff proposals. The formal rulemaking process, including a Notice of Proposed Rulemaking, public comment period, and Board consideration, has not yet begun.

How CARB Proposes to Define Organizational Boundaries

Before calculating emissions, your company needs to define which operations are included. CARB staff have proposed two approaches for public feedback:

• Equity share approach: account for emissions proportional to your ownership stake in each operation. Relevant for minority joint ventures where you share economic benefits without direct operational control.
• Control approach (financial): account for 100% of emissions from operations where you direct financial and operating policies to generate economic benefits.
• Control approach (operational): account for 100% of emissions from operations where you have authority to introduce and implement operating policies, regardless of ownership.

Under the proposed framework, companies would be required to disclose not just which method they used, but why. CARB is also actively seeking feedback on whether other boundary approaches should be considered. The final rules will be set through formal rulemaking. For companies with subsidiaries, joint ventures, or complex holding structures, this decision will directly shape the emissions figures your investors and regulators see.

Proposed GHG Accounting Methods and Emission Factors

CARB staff have presented four calculation methods for Scope 3 estimation, all currently out for public feedback:

• Spend-based: multiplies the financial value of purchased goods or services by an emissions factor. The most accessible starting point for most companies.
• Activity-based: uses physical activity data such as kilometers traveled or kilograms purchased, multiplied by emission factors. More accurate when operational data is available.
• Supplier-specific: uses primary emissions data collected directly from suppliers at a product or process level. Most granular, most data-intensive.
• Hybrid: combines the above methods across different Scope 3 categories to balance accuracy with feasibility.

On emission factor datasets, CARB has proposed drawing from EPA eGRID, the IPCC Emissions Factor Database, EPA’s Emission Factors Hub, and the U.S. Environmentally-Extended Input-Output model (USEEIO). Under the proposed framework, reporters would document their chosen factors and explain any year-over-year changes. The final list of approved datasets and documentation requirements will be confirmed through rulemaking.

Three Proposed Options for Scope 3 Reporting from 2027

CARB has not finalized how Scope 3 reporting will be structured. Three options are on the table. Stakeholder feedback due by April 13, 2026 will directly influence which path is taken. Your data preparation strategy should account for all three possibilities.

Option 1: Broad Applicability

All 15 Scope 3 categories required from 2027. Companies may designate certain categories as de minimis with explanation. Strongest alignment with the GHG Protocol and EU CSRD, but requires comprehensive value chain data from day one.

Option 2: Sectoral Phase-In

Starts with transportation and industrial sectors in 2027. Aligns with California’s Climate Change Scoping Plan, which identifies these sectors as responsible for the largest share of statewide emissions. Transportation alone accounted for 38% of California’s 360.4 MMT CO2e total in 2023. Initial coverage would expand to technology, energy, cement, and other manufacturing.

Option 3: Category Phase-In

Starts with the five most commonly disclosed Scope 3 categories based on current corporate practice, with the remaining ten voluntary. The five priority categories are: Business Travel (47.5% of companies currently reporting), Purchased Goods and Services (42.5%), Fuel and Energy-Related Activities (40.6%), Employee Commuting (39.6%), and Waste Generated in Operations (37.2%). Data from a 2024 study of 497 companies by Delmas, Clark, Li, and Timmer.

Proposed Assurance Standards for Scope 1 and 2

CARB staff have proposed requiring limited assurance for Scope 1 and 2 from 2027. Five standards are currently proposed for acceptance:

• AA1000 Assurance Standard v3 (AA1000AS v3)
• AICPA AT-C Section 210 (limited assurance) and AT-C Section 205 (reasonable assurance)
• ISAE 3000 (Revised) and ISAE 3410, proposed until December 2026
• ISSA 5000, proposed from December 2026, replacing ISAE 3410
• ISO 14064-3:2019 with provider qualifications under ISO 14065 and ISO 14066

These are proposals under active public feedback. The final list will be confirmed through rulemaking. That said, all five standards have strong international footing. ISSA 5000 is being adopted across the EU, UK, Japan, Australia, India, South Korea, and others. ISO 14064-3 is recognized in over 100 jurisdictions. If your company already reports under the CSRD or IFRS S2, your assurance setup is likely directionally compatible.

What Will SB 253 Compliance Cost? CARB’s Initial Estimates

CARB presented preliminary cost estimates at the March 23 workshop, drawn from SEC rulemaking feedback and adjusted to 2025 dollars using the California Consumer Price Index. These are illustrative figures and will be refined through the formal Standardized Regulatory Impact Assessment process.

Estimated ongoing annual costs per entity:

• Scope 1 and 2 reporting: $73,544
• Scope 1, 2, and 3 reporting: $87,498
• Limited assurance for Scope 1 and 2: $55,213
• Total: $142,711

Year 1 costs are higher due to one-time setup. The table below shows average annual costs across the three-year implementation window by option.

Across all three options, the maximum annual cost per entity is less than 0.02% of the $1 billion revenue threshold. The compliance cost is manageable. The risk of being unprepared is not.

Conclusion

The August 10, 2026 deadline is confirmed and approaching. The 2027 framework is still being shaped, and your input matters. Public comments are open until April 13, 2026.

Four priorities for your leadership team:

• Confirm applicability. Verify your entity meets the $1 billion revenue threshold and the doing business in California definition adopted in February 2026.
• Start Scope 3 measurement now. Regardless of which option CARB selects, the underlying data work is the same. Build your inventory across all 15 categories.
• Engage your assurance provider. Initiate conversations about the proposed limited assurance requirement for 2027 under one of the five proposed standards.
• Submit public comments. The Scope 3 option CARB adopts will shape your compliance obligations for years. Stakeholder input deadline is April 13, 2026.

ASUENE provides enterprise-grade carbon accounting and Scope 3 measurement solutions built for SB 253 and aligned with IFRS S2, the GHG Protocol, and CARB’s developing framework. Contact the ASUENE team today to assess your readiness and build your path to compliance.

Why Work with ASUENE Inc.?

ASUENE is a key player in carbon accounting, offering a comprehensive platform that measures, reduces, and reports emissions, including Scope 1-3. ASUENE serves over 10,000 clients worldwide, providing an all-in-one solution that integrates GHG accounting, ESG supply chain management, a Carbon Credit exchange platform, and third-party verification.

ASUENE supports companies in achieving net-zero goals through advanced technology, consulting services, and an extensive network.