California’s SB 253, the Climate Corporate Data Accountability Act, is the most consequential GHG disclosure mandate ever enacted in the United States. For any company with more than $1 billion in annual revenues doing business in California, this is now a legal obligation with enforcement teeth. If your organization is still treating SB 253 as a future problem, the first reporting deadline is closer than most compliance teams realize.
This article covers exactly what the law requires, who is in scope, when filings are due, what assurance means in practice, and how companies that already navigated Europe’s CSRD are building on that experience to move faster.
Table of contents
- What SB 253 actually requires
- Who is in scope
- Key deadlines
- Assurance requirements
- Penalties for non-compliance
- SB 253 and CSRD: structural parallels
- How Dcycle supports SB 253 compliance
What SB 253 actually requires
SB 253 mandates annual public disclosure of greenhouse gas emissions across three scopes, following the GHG Protocol Corporate Standard:
Scope 1 covers direct emissions from sources owned or controlled by the company, such as combustion in company-owned facilities and vehicles.
Scope 2 covers indirect emissions from purchased electricity, heat, steam, or cooling.
Scope 3 covers all other indirect emissions in the value chain, including purchased goods and services, capital goods, upstream transportation, waste, business travel, employee commuting, downstream logistics, use of sold products, and end-of-life treatment. These 15 categories represent the majority of most companies’ emissions footprint, and they are typically the hardest to quantify.
Disclosures must be filed annually with a state-designated reporting organization (currently CARB, the California Air Resources Board) and must be publicly accessible. The law specifies that reports follow the GHG Protocol methodology, meaning companies cannot use proprietary or ad hoc frameworks.
Who is in scope
The threshold is straightforward: any company with total annual revenues exceeding $1 billion that does business in California. The law does not require that the company be headquartered in California or be a California entity. A company incorporated in Delaware, headquartered in Texas, and generating 10% of its revenue from California customers still falls within scope.
This makes SB 253 unusually broad. California’s GDP is the fifth largest in the world. Most major US corporations, and a significant number of large international companies, do some level of business in the state. Estimates suggest 5,000 or more companies are affected.
SB 253 applies to both public and private companies. That is a meaningful departure from SEC climate disclosure frameworks, which historically focused on publicly traded issuers.
Key deadlines
The reporting timeline is phased:
2026 (first filing for fiscal year 2025): Companies must disclose Scope 1 and Scope 2 emissions. The exact filing deadline within 2026 will be set by CARB, but companies need data collection and calculation processes in place now to cover the full 2025 fiscal year.
2027 (first filing for fiscal year 2026): Scope 3 emissions disclosure begins. This is where the complexity spikes sharply, as Scope 3 requires supplier data, activity-based or spend-based estimates across 15 categories, and defensible boundary decisions.
Ongoing: The law contemplates phased introduction of assurance requirements, with timelines subject to CARB rulemaking.
These deadlines are not aspirational. Companies that have not started building their emissions inventory for FY2025 are already running late.
Assurance requirements
SB 253 introduces mandatory third-party assurance for reported emissions, with a phased approach:
Limited assurance is required first. This means an independent assurance provider reviews the report and confirms there is no evidence of material misstatement. It is a lower bar than a full financial audit, but it requires documented methodologies, traceable data sources, and a structured review process.
Reasonable assurance is required at a later stage (exact timing subject to CARB rulemaking). This is a higher standard, comparable to a financial statement audit, requiring the assurer to reach a positive conclusion that the reported data is accurate.
The assurance requirement is what separates SB 253 from voluntary disclosure frameworks like CDP. Companies cannot simply self-report a number and call it done. Every data point in the GHG inventory needs to be traceable to its source, every methodology decision documented, and every calculation auditable.
Penalties for non-compliance
CARB can impose civil penalties of up to $500,000 per year for failure to report, and up to $500,000 per year for reporting inaccurate data. These penalties apply to each reporting cycle, not as a one-time cap. Willful non-disclosure or knowing submission of false data can trigger additional enforcement action.
Beyond direct penalties, companies face reputational and litigation risk. California’s consumer protection framework creates exposure for companies that misrepresent their climate commitments or fail to meet publicly stated obligations.
SB 253 and CSRD: structural parallels
The structural DNA of SB 253 closely resembles the EU’s Corporate Sustainability Reporting Directive (CSRD), which has required mandatory GHG disclosure, Scope 1/2/3 coverage, and third-party assurance from European companies since 2024.
Both mandates require:
- Mandatory Scope 1, 2, and 3 GHG disclosure following established methodologies
- Independent assurance of reported data
- Annual public reporting
- Coverage of both direct and value chain emissions
The key practical difference is that CSRD is embedded in a broader double materiality framework requiring disclosure on topics beyond emissions, while SB 253 focuses specifically on GHG data. But the data infrastructure needed, the supplier engagement processes, the audit trail requirements, and the assurance protocols are substantially the same.
This matters for US companies with European parent companies or subsidiaries, which may already be inside CSRD’s scope. For those companies, SB 253 data collection can be consolidated with existing CSRD workflows rather than treated as a separate parallel process.
For companies without CSRD exposure, the experience of European companies navigating CSRD implementation since 2024 offers a clear roadmap. The mistakes made in Europe, around Scope 3 boundary decisions, supplier data gaps, methodology inconsistencies, and assurance readiness, do not need to be repeated.
How Dcycle supports SB 253 compliance
Dcycle already supports over 2,000 companies across CSRD, GHG Protocol, CDP, CSDDD, and 15+ frameworks. The platform was built specifically for the kind of multi-scope, multi-entity GHG inventory that SB 253 requires.
Data collection: Dcycle centralizes emissions data collection from multiple facilities, subsidiaries, and business units into a single inventory. For Scope 2, both market-based and location-based methods are supported. For Scope 3, the platform covers all 15 categories with activity-based and spend-based calculation paths.
Audit trail and assurance readiness: Every data point in Dcycle carries full traceability, including source, methodology, assumption, and calculation logic. This documentation layer is what assurance providers need to conduct their review efficiently. Companies that lack this infrastructure typically require months of remediation before their first assurance engagement.
Multi-framework output: Companies facing both SB 253 and CSRD obligations (or CDP, ISSB, GRI) do not need to collect data twice. Dcycle’s framework-agnostic data layer maps a single collection effort to multiple reporting outputs simultaneously.
Expert guidance: Dcycle’s advisory team has hands-on experience helping companies through CSRD assurance cycles in Europe. That expertise transfers directly to SB 253 assurance preparation.
To see how Dcycle structures SB 253 readiness assessments, request a demo.
If you are also navigating CSRD alongside SB 253, the CSRD resource hub covers the European framework in depth. For deeper context on Scope 3 specifically under SB 253, read Scope 3 under SB 253: the hardest part of California’s climate law.