California SB 253 Compliance Guide: Climate Corporate Data Accountability Act

Status, September 2026: SB 253 is in force. CARB approved its first regulations in February 2026, withdrew them in June for changes, and re-proposed them in July; the first Scope 1 and 2 reports are now due November 10, 2026. Scope 3 reporting starts in 2027, and CARB has proposed limiting it to five categories. Source: Mayer Brown.

Overview

California Senate Bill 253, the Climate Corporate Data Accountability Act, signed into law in October 2023, establishes the most expansive mandatory greenhouse gas emissions reporting requirement in the United States. The law requires large companies doing business in California to publicly disclose their Scope 1, Scope 2, and Scope 3 greenhouse gas emissions, making California the first U.S. state to mandate full value chain emissions reporting.

SB 253 applies to both public and private companies—a critical distinction from the SEC's 2024 climate rule, which would have applied only to SEC registrants and never took effect. The revenue threshold of $1 billion captures a broad swath of the corporate landscape, including privately held companies, U.S. subsidiaries of foreign groups, and companies across every sector of the economy.

The California Air Resources Board (CARB) is the implementing agency, tasked with developing detailed regulations that specify reporting methodologies, timelines, and the digital reporting platform. CARB's implementing regulations, initially expected by January 2025, have been subject to delay and refinement, reflecting the complexity of operationalizing full value chain emissions reporting for thousands of companies. CARB's board approved initial regulations in February 2026 and re-proposed them with changes in July 2026, setting November 10, 2026 as the first deadline for Scope 1 and 2 reports. In September 2026 the revised regulations were still awaiting final approval from California's Office of Administrative Law, so companies should keep monitoring CARB's rulemaking.

Who Does It Apply To?

SB 253 applies to reporting entities defined as partnerships, corporations, limited liability companies, or other business entities with total annual revenues exceeding $1 billion that "do business in California" as defined under existing California tax law (Revenue and Taxation Code Section 23101).

Key points on applicability:

• Revenue threshold: $1 billion in total annual revenues. This is entity-level revenue, not California-specific revenue.
• Doing business in California: Under California tax law, this includes entities that are organized in California, have sales in California, own or use property in California, or have compensation paid in California exceeding specified thresholds. The threshold for "doing business" is notably low.
• Entity type: Both public and private entities are covered, with no exemption for privately held companies or partnerships. The entity must be formed under the laws of California, another U.S. state or the District of Columbia, or federal law, so companies organized abroad are not covered directly, but their U.S. subsidiaries can be.
• Exclusions: There are no industry-wide sector exemptions, but CARB's regulations, still pending final approval, exclude nonprofits, government entities, businesses whose only California activity is interstate wholesale electricity transactions or paying employees there (such as teleworkers), and, for 2026 reports only, insurers.
• Estimated scope: When CARB published a preliminary list of potentially covered companies in September 2025, staff estimated that roughly 2,600 companies are subject to SB 253. The list relies on 2022 data and is not definitive, so each company must assess its own status.

Companies should assess their California nexus carefully. The "doing business in California" standard is broad and captures many entities that may not have a significant physical presence in the state.

Key Requirements

1. Scope 1 and Scope 2 Emissions Reporting Reporting entities must annually disclose Scope 1 (direct) and Scope 2 (indirect from purchased energy) GHG emissions. Emissions must be quantified in accordance with the GHG Protocol Corporate Standard or an equivalent methodology approved by CARB.

2. Scope 3 Emissions Reporting Reporting entities must disclose Scope 3 (value chain) emissions starting in 2027. The statute points to the GHG Protocol's Corporate Value Chain Standard and its 15 categories, but CARB has proposed limiting mandatory Scope 3 reporting, for now, to five of them: purchased goods and services, fuel- and energy-related activities, waste generated in operations, business travel, and employee commuting. The other ten categories would stay voluntary. The law includes a safe harbor provision recognizing the inherent uncertainty in Scope 3 data.

3. GHG Protocol Methodology Emissions must be quantified using the Greenhouse Gas Protocol Corporate Accounting and Reporting Standard and the Corporate Value Chain Standard, or equivalent standards established by CARB. This provides methodological consistency with international practice.

4. Independent Assurance Scope 1 and Scope 2 emissions must be verified by an independent third-party assurance provider. CARB's regulations require no assurance for the first reports in 2026; CARB has proposed starting limited assurance with reports filed in 2027, and the statute moves Scope 1 and 2 to reasonable assurance in 2030, when limited assurance of Scope 3 is also slated to begin. CARB sets the assurance standards and provider qualifications through its rulemaking.

5. Public Disclosure on Digital Platform Emissions data must be reported on a publicly accessible digital reporting platform managed by CARB. This means emissions data will be available to investors, customers, competitors, civil society, and the general public—a significant transparency commitment.

6. Consolidated Reporting The obligation attaches to each entity that meets the revenue threshold, but reports may be consolidated at the parent company level: under SB 219, a subsidiary that qualifies on its own does not need a separate report if it is covered by its parent's. CARB's regulations set out how parent reports cover subsidiaries.

Timeline & Milestones

*Dates reflect CARB's revised regulations released in July 2026, which were awaiting final approval from California's Office of Administrative Law in September 2026. SB 219 (2024) amended some SB 253 provisions, including extending CARB's rulemaking deadline. Monitor CARB's rulemaking for final dates.

Step-by-Step Compliance Roadmap

Step 1: Applicability Determination

Assess whether your entity meets the $1 billion revenue threshold and the "doing business in California" standard. Review California Revenue and Taxation Code Section 23101 and consult with tax counsel. Identify which legal entities within your corporate structure trigger the obligation. Determine whether CARB's implementing regulations affect your entity classification.

Step 2: GHG Inventory Development

Establish or strengthen your GHG emissions inventory in accordance with the GHG Protocol. Define organizational boundaries (equity share or control approach) and operational boundaries. Compile Scope 1 and Scope 2 emissions data with sufficient granularity for independent verification. Begin cataloging Scope 3 emission sources across all 15 categories, prioritizing categories by materiality and data availability.

Step 3: Scope 3 Methodology and Data Collection

Develop a Scope 3 measurement methodology that balances accuracy with feasibility. Engage key suppliers to obtain primary emissions data where possible. For categories where primary data is unavailable, establish spend-based or activity-based estimation approaches using recognized emission factors. Document all methodologies, assumptions, and data sources. The safe harbor provision protects good-faith efforts, but robust documentation is essential.

Step 4: Assurance Preparation

Select an independent assurance provider qualified under CARB's forthcoming standards. Implement internal controls over emissions data collection, calculation, and reporting that mirror financial reporting controls. Conduct a dry run of the assurance process to identify data quality issues before limited assurance begins with reports filed in 2027.

Step 5: Reporting and Continuous Improvement

Prepare and submit emissions data on CARB's digital platform by the applicable deadline. Include all required disclosures and, once limited assurance applies (proposed for 2027), the assurance provider's report. After the first reporting cycle, identify areas for data quality improvement—particularly in Scope 3 categories relying on estimates. Expand primary data collection with suppliers and business partners in subsequent years.

Common Pitfalls

Assuming private company exemption. Unlike the SEC's 2024 climate rule, which covered only SEC registrants and never took effect, SB 253 applies to private companies. Many privately held companies with $1 billion or more in revenue have never been required to publicly disclose emissions data. The transition from no disclosure to full Scope 1/2/3 public reporting is a significant operational undertaking that requires early preparation.

Underestimating the "doing business in California" breadth. The California tax nexus standard is broad. Companies with relatively modest California sales or operations may still qualify. Do not assume you are outside scope without a thorough legal analysis.

Treating Scope 3 safe harbor as a free pass. The safe harbor protects companies from liability for good-faith Scope 3 estimates that later prove inaccurate. It does not excuse failure to report Scope 3 or the use of clearly unreasonable methodologies. Companies must demonstrate genuine effort to measure value chain emissions using appropriate data and methods.

Ignoring overlap with other mandates. Companies subject to SB 253 may also face requirements under California SB 261 (once its court-ordered hold ends), the CSRD, or other jurisdictions' mandates. A fragmented approach to emissions reporting across these frameworks wastes resources. Build a single, robust emissions inventory that serves multiple reporting obligations.

How Council Fire Can Help

Council Fire helps companies confronting SB 253's requirements build emissions measurement capabilities that are both compliant and strategically valuable. We approach GHG reporting not as a box-checking exercise but as a foundation for genuine climate strategy.

Our Scope 3 measurement expertise is particularly relevant for SB 253 compliance. We help clients prioritize the 15 Scope 3 categories, design supplier engagement programs, and establish estimation methodologies that pass assurance scrutiny while providing actionable strategic insights.

For companies new to mandatory emissions reporting, Council Fire provides end-to-end implementation support—from organizational boundary definition through assurance readiness. Our climate resilience team ensures that the data and processes built for SB 253 compliance also inform risk management, target-setting, and investor communication.

Council Fire's stakeholder engagement expertise helps companies manage the public disclosure dimension of SB 253. When your emissions data is publicly available on CARB's platform, having a clear narrative about your climate strategy and improvement trajectory is essential.

Frequently Asked Questions

Does SB 253 apply to companies headquartered outside California?

Yes. SB 253 applies to any entity formed under U.S. law (California, another state, the District of Columbia, or federal law) that is "doing business in California" with annual revenues exceeding $1 billion, regardless of where the entity is headquartered. The "doing business" standard under California tax law is broad and includes entities with sales, property, or employees in California above specified thresholds. Companies organized outside the United States are not reporting entities themselves, but their U.S. subsidiaries can be, so foreign groups with California operations or sales channels should assess each U.S. entity carefully.

What is the Scope 3 safe harbor provision?

SB 253 includes a safe harbor that shields reporting entities from administrative penalties for misstatements in their Scope 3 emissions disclosures, provided those disclosures have a reasonable basis and are made in good faith. Between 2027 and 2030, Scope 3 penalties can be assessed only for failure to file. This recognizes the inherent uncertainty in value chain emissions data. However, the safe harbor does not apply to Scope 1 and 2 reporting, and it does not protect against claims based on fraudulent or intentionally misleading disclosures.

How does SB 253 interact with SB 261?

SB 261, the Climate-Related Financial Risk Act, is a companion law requiring companies with annual revenues over $500 million doing business in California to prepare biennial reports on climate-related financial risks in alignment with TCFD recommendations. Unlike SB 253, it is on hold: on November 18, 2025, the Ninth Circuit barred its enforcement while an appeal proceeds, and CARB will set a new first-report date once the appeal is resolved. SB 253 and SB 261 are distinct laws with different requirements, thresholds, and timelines, but they share a common goal of increasing climate transparency. Companies exceeding $1 billion in revenue will be subject to both once the hold on SB 261 ends. The data and processes developed for SB 253 emissions reporting directly support the SB 261 risk disclosure requirements.

What are the penalties for non-compliance?

SB 253 authorizes administrative penalties of up to $500,000 per reporting year for failing to file, filing late, or otherwise failing to meet its requirements. For the first reports in 2026, CARB has said it will follow its December 2024 enforcement notice and not penalize companies that make a good-faith effort using the data they already have. Companies should note that public availability of the data also creates reputational consequences for non-compliance or clearly inadequate reporting.