California Air Resources Board Hosts Workshop to Support Development of the California Corporate Greenhouse Gas Reporting Program

On March 23, 2026, the California Air Resources Board (CARB) hosted a virtual public workshop with stakeholders to support the development of California’s corporate greenhouse gas (GHG) emissions reporting program established by the Climate Corporate Data Accountability Act, as amended by SB 2191 (see Deloitte’s October 1, 2024, Heads Up for more information about SB 219). The objectives of the workshop were to (1) summarize initial regulations approved during the CARB board hearing held on February 26, 2026;2 (2) cover the next stage in regulatory development; and (3) address proposed staff concepts related to the development of GHG emissions reporting program requirements. CARB outlined these key staff concepts, which are publicly available, and solicited feedback on the staff concepts presented for GHG emission reporting and assurance, as further detailed below.

CARB’s presentation largely focused on the requirement to report Scope 1, 2, and 3 emissions in 2027 (including obtaining limited assurance on Scope 1 and 2 emissions) and annually thereafter. CARB stated that it is in the “pre-rulemaking” phase for the following key GHG emission reporting items:

• Scope 1, 2, and 3 framework.
• Organizational boundaries.
• GHG accounting methods.
• Emissions factors.
• Scope 3 options.
• Assurance.
• Economic analysis.

Although CARB’s GHG emission reporting approach is largely aligned with definitions and accounting methods in the GHG Protocol corporate standard and corporate value chain (Scope 3) standard, the reporting template and phase-ins under consideration (discussed below) may differ in many respects from the requirements of the GHG Protocol. The sections below summarize CARB’s regulatory approach for GHG accounting. CARB’s presentation contains more detailed definitions.

CARB’s proposed staff concepts related to setting organizational boundaries would give entities the option of selecting either an equity share approach or a control approach (i.e., financial control or operational control). Entities would not be required to use a specific approach but would need to disclose the organizational boundaries selected.

CARB gave an overview of GHG emissions scopes, including the definitions of Scope 1, 2, and 3 emissions, and reminded participants of the October 2025 GHG emissions reporting draft template released for public feedback. Further, CARB noted that a revised draft reporting template for Scope 1 and 2 emissions is expected to be released for public feedback by the summer of 2026. Unlike the October 2025 template, the revised template would be required for 2027 reporting and beyond.

CARB’s staff concepts would allow flexibility in GHG emission calculation methods for Scope 3 emissions. Entities would be able to use any of the following GHG accounting methods: spend-based, activity-based, supplier-specific, or hybrid (mix of the methods allowed). CARB indicated that entities would need to decide which method to use by considering resourcing, available data, and objectives. Entities would be required to disclose the method used but would not be required to obtain direct supplier-specific data.

CARB discussed how emission factors3 are a key input in the measurement of GHG emissions and identified certain publicly available data sets. In addition, CARB proposed the following sources for potential emission factors for Scope 3 categories:

• The EPA’s Emissions & Generation Resource Integrated Database (eGRID).
• The IPCC’s Emissions Factor Database.
• The EPA’s GHG Emissions Factor Hub.
• U.S. Environmentally-Extended Input-Output models.

SB 253 requires Scope 3 emissions reporting beginning in 2027 on prior-year emissions. CARB introduced three staff concepts for regulatory adoption of Scope 3 emissions reporting. The first option, broad applicability, would require all reporting entities to report all Scope 3 categories in 2027 but would give them the flexibility not to report categories deemed “de minimis.” Under the second option, sectoral phase-in, Scope 3 reporting would be required in 2027 only for the sectors CARB has identified as responsible for the largest share of statewide emissions (i.e., transportation and industrial sectors); other sectors would report in the following years. The third option, category phase-in, would require all reporting entities to report Scope 3 emissions in 2027, beginning with the most reported Scope 3 categories;4 the phase-in of other categories would occur in the following years.

To support initial implementation of SB 253 in 2026 on prior-year emissions, CARB has issued an enforcement notice indicating that it will exercise discretion for an entity’s first reports issued in 2026, and such reports may be submitted regardless of whether the data have received limited assurance. Starting in 2027, CARB has proposed the following staff concepts associated with assurance standards that are accepted in other jurisdictions:

• AccountAbility’s AA1000 Assurance Standard (AA1000AS v3).
• AICPA standards (AT-C Section 2105 [limited assurance] or AT-C Section 2056 [reasonable assurance])
• ISAE 30007 (revised) and ISAE 34108 (until December 2026).
• ISSA 50009 (effective December 2026).
• ISO 14064-3:201910 (ISO 14065/ISO 14066 — provider qualifications).

CARB has specifically included AICPA standards to ensure “domestic CPA firms already providing financial audit services to California reporting entities can perform GHG assurance engagements without requiring entities to engage a separate provider solely for SB 253 compliance.” This approach is consistent with other regulated GHG disclosure regimes, such as the European Union’s Corporate Sustainability Reporting Directive.

CARB is required to determine the economic impact of these regulations and proposed staff concepts on estimating costs.

CARB has opened a public docket for stakeholders to provide feedback on concepts covered, alternative methods CARB should consider, and questions posed during this workshop. Comments are due by April 13, 2026.

For more information on the virtual workshop, see CARB’s Web site.