On July 21, 2026, the California Air Resources Board (CARB) held its fifth public workshop on implementation of Senate Bill 253, the Climate Corporate Data Accountability Act. SB 253 requires U.S.-based companies doing business in California with more than $1 billion in annual revenue to publicly disclose their greenhouse gas (GHG) emissions; Scope 1 and 2 beginning with the 2026 reporting cycle, and Scope 1, 2, and 3 beginning with the 2027 cycle.
The workshop primarily focused on reporting requirements for 2027 and beyond, but the concepts discussed remain at the pre-rulemaking stage. CARB indicated that it will release a formal draft rule later this year, which will be followed by a 45-day public comment period. Accordingly, the concepts discussed at the workshop are subject to change before that draft is issued.
Below, we summarize the most significant takeaways from the workshop.
The 2026 Reporting Deadline Is Being Pushed to Nov. 10
CARB confirmed that the final regulatory package including the initial regulations implementing SB 253 (submitted to the Office of Administrative Law on May 20, 2026) has been withdrawn to permit the agency to make narrow clarifying edits before resubmission. As part of that process, CARB has proposed moving the 2026 Scope 1 and Scope 2 reporting deadline from August 10 to November 10, 2026, to give companies additional time following formal adoption of the rule.
CARB indicated that it intends to provide supplemental guidance, including a voluntary online intake platform for fee contact information and GHG emissions reporting, an instructional video, and a companion guidance document by September 1, 2026.
The 2027 Framework Will Track the GHG Protocol, With California-Specific Overlays
For the rules taking effect in 2027, CARB staff described a drafting approach that leans heavily on the Greenhouse Gas Protocol (Corporate Standard, Scope 2 Guidance, and Scope 3 Standard), while adding California-specific language where needed to satisfy SB 253's statutory directives or state administrative law requirements. CARB framed this as an effort to maximize interoperability with other disclosure regimes, including the EU's Corporate Sustainability Reporting Directive and the IFRS S2 standard.
Notably, the GHG Protocol is currently revising its 2015 Scope 2 Guidance, with an updated standard expected in 2027. CARB indicated its regulation will incorporate only the existing 2015 version as a fixed reference, since California administrative law does not permit “dynamic” incorporation of future changes to outside standards. Updating the incorporated standard would require separate CARB rulemaking. In the interim, it is possible that companies may need to calculate Scope 2 emissions differently for California than under other regimes that adopt the revised guidance sooner.
General Reporting Requirements
Beyond the scope-specific rules, CARB previewed a set of general requirements meant to apply across Scope 1, 2, and 3 disclosures. At a high level, these would require companies to:
- Disclose the quantification methods and measurement approaches used for the calculation of emissions
- Assess and disclose measurement uncertainty, using a qualitative explanation where a quantitative estimate isn’t feasible or would be unreasonably burdensome
- Identify and document any missing data and any substitute sources or estimation methods used to fill those gaps
- Report biogenic CO2 emissions separately from Scope 1, 2, and 3 totals, while folding any associated methane and nitrous oxide emissions into the relevant Scope 1, 2 or 3 emissions inventories.
- Separately disclose any voluntary emissions reductions or removals (e.g., carbon credits or land-management sequestration), rather than netting them against reported totals
- Justify and disclose the basis for any data exclusions, including an estimate of the excluded emissions where quantifiable
- Disclose material changes in methodology from year-to-year and recalculate prior-year data if cumulative structural or methodological changes exceed 5% of base-year emissions
Scope 2 Reporting Will Require Dual Methodologies
CARB's proposed approach to Scope 2 would require companies to calculate and report emissions using both the market-based and location-based methods, broken out by source type (electricity, steam, heating, and cooling). Companies would also need to report Scope 2 emissions separately for each greenhouse gas (carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride) expressed in metric tons of CO2 equivalent, in addition to the combined CO2 equivalent total. Where emission factors are unavailable for a particular region or energy source, companies would need to document that omission in its inventory.
Scope 3 Reporting Will Phase-In Through Five Categories
Responding to concerns about cost and data availability, CARB confirmed it will require reporting on only five of the fifteen Scope 3 categories beginning in 2027:
- Purchased Goods and Services (Category 1)
- Fuel- and Energy-Related Activities (Category 3)
- Waste Generated During Operations (Category 5)
- Business Travel (Category 6)
- Employee Commuting (Category 7)
According to CARB, these categories were selected because they tend to have the most mature data sources and calculation methodologies. The remaining 10 categories would remain voluntary for 2027, with CARB declining to commit to a timeline for expanding the mandatory list.
For each required category, companies would need to identify the activities included in the emissions inventory, disclose their quantification and accounting methods and data types, report total emissions generated during the reporting period in metric tons of CO2 equivalent, explain any exclusions, and state what percentage of the category’s emissions were calculated using primary (rather than estimated or industry-average) data, along with the quantification method used for primary data.
Limited Assurance Will Be Required Starting in 2027
Beginning with reports submitted in 2027, in-scope companies would need to obtain a limited assurance engagement over their Scope 1 and Scope 2 emissions (including biogenic CO2) from a qualified independent third-party assurance provider. CARB has proposed accepting any of five recognized assurance frameworks; AA1000 Assurance Standard (AA1000AS v3), American Institute of Certified Public Accountants (AICPA AT-C Section 210), International Standard on Assurance Engagements (ISAE) 3410 paired with ISAE 3000 (Revised), for engagements commencing before December 15, 2026, International Standard on Sustainability Assurance (ISSA) 5000 for engagements commencing on or after December 15, 2026, or International Organization for Standardization (ISO) 14064-3:2019 (with additional accreditation requirements). The assurance report itself would need to identify the assurance standard applied and level of assurance provided, the emissions covered, the provider's conclusion, the provider's identifying and contact information, and the date the assurance engagement was completed.
Insurers Will No Longer Be Exempt Starting in 2027
The initial 2026 regulation exempted insurance companies from GHG reporting to avoid duplicating parallel disclosures to the California Department of Insurance (CDI). Following further review directed by the CARB board, staff concluded that CDI's reporting regime does not cover Scope 3 emissions or include an assurance component and, therefore, will not fully satisfy SB 253 once the 2027 requirements take effect. Under the proposed approach, insurers could submit their CDI filing in 2027 to CARB to satisfy SB 253, provided it meets all applicable requirements. Otherwise, they would need to supplement their CDI report with the missing information.
What's Next
CARB will hold six sector-specific virtual listening sessions between August 5 and September 9, 2026, covering data users and public-interest groups, manufacturing and industrials, agriculture and food, energy and transportation, retail and technology, and financial services and insurance. These sessions are intended to gather stakeholder input rather than convey new information.
A formal draft of the 2027 regulation is expected later this year and will be followed by a 45-day public comment period before it goes to the CARB board for consideration.