CARB’s Updates on Rulemaking for 2027 and Beyond for California SB 253 

CARB has begun its second round of rulemaking for California SB 253 on GHG emission disclosures. Finalized regulations are expected by the end of the year and will include reporting requirements for 2027 and beyond. 

• CARB has begun the rulemaking process for reporting GHG emissions under SB 253 in 2027 and beyond, having held two public workshops presenting their initial staff concepts.  

• CARB has shared proposed general reporting requirements and specific recommendations for scope 2 and scope 3 disclosures, including a category-based phase in approach. None of the proposals are finalized at this stage.  

• CARB has nearly finalized their first round of rulemaking on California’s Climate Accountability Package (“the 200s”). Additional information on 2026 rulemaking can be found here. 

In their July 21, 2026 Workshop, CARB presented proposed staff concepts on reporting requirements under SB 253 for 2027 and beyond. These built on the initial staff concepts shared in their March workshop. You can find a copy of their materials here. Note that all concepts discussed in the workshop and summarized below remain a proposal and will not be finalized until the rulemaking package is approved. CARB noted they expect to send this rulemaking package to the Board by the end of 2026.  

General Reporting Requirements 

CARB has proposed general reporting requirements including: 

• Greenhouse Gas Disclosure,  

• Standards and Guidance,  

• Quantification Methodologies,  

• Measurement Uncertainty,  

• Missing Data Protocols and Substitution Procedure,  

• Reporting Biogenic Emissions,  

• Reporting Emissions Reductions or Removals,  

• Data Exclusions,  

• Notifying CARB of Changes to Methodologies,  

• Recalculation of Previous Year Data, and  

• Supplemental Information.  

In general, CARB has indicated they will align with the GHG Protocol by implementing their requirements and their recommendations where aligned with SB 253 objectives, while proposing additional language needed to ensure the requirements are appropriate to the California regulatory context. CARB has also shared a proposed reporting deadline of November 10^th annually, beginning in 2027, to align with the 2026 reporting deadline. Below is a summary of their proposals:

Greenhouse Gas Disclosure 

CARB would require companies to disclose their gross scope 1, 2, and 3 GHG emissions during the reporting period in metric tons of CO₂ equivalent (CO₂e). 

Standards and Guidance 

Reporting companies would be required to quantify their emission in adherence with the GHG Protocol Corporate Standard, Scope 2 Guidance, and Scope 3 Standard. 

Quantification Methodologies 

Reporting companies would need to disclose their quantification methods and measurement approaches used to calculate their GHG emissions, including:  

• Consolidation approach for organizational boundaries 

• Global Warming Potential values and assessment report vintage 

• Emission factor sources for all calculations with key attributes (i.e. vintage, geographic and technical representativeness, uncertainty) 

• Quantification method (e.g. direct measurement or calculation-based method), including any process-specific tools or models used 

Measurement Uncertainty 

Reporting companies would need to assess the uncertainty associated with the quantification methodologies used and report confidence intervals with data points, where applicable. If quantitative estimation of uncertainty isn’t feasible or would impose an unreasonable burden, companies could instead provide an explanation and conduct a qualitative assessment of uncertainty instead.  

Missing Data Protocols and Substitution Procedure 

Reporting companies would need to identify any missing data or parameters in their emissions accounting and document any substitute data sources or estimation methods used. This would also require disclosure of the basis for selecting the substitution or estimation approach and any assumptions. This requirement is in line with similar provisions under California’s Mandatory Reporting Regulation.  

Reporting Biogenic Emissions 

Reporting companies would also need to calculate biogenic CO₂ emissions from the combustion, consumption, or biodegradation of biomass and biomethane and report those emissions separately from their scope 1, 2, and 3 emissions totals. If a reporting entity is already reporting under other California regulations, they may quantify biogenic emissions in line with the requirements of those programs, provided they disclose which regulation they are aligning with. If not already reporting to other California regulations, entities can utilize either the GHGP Corporate Standard, other quantification methodologies, or other regulations, but they must disclose which methodology they are aligning with.  

Similar to other emissions reporting requirements, companies would need to disclose tracking units, quantification methods, emission factors, and other data sources used to calculate biogenic emissions. Biogenic emissions would be held to the same assurance requirements as the emissions reported under scope 1, 2, and 3. 

Reporting Emissions Reductions or Removals 

Reporting companies may also include any voluntary investments, management activities, or other activities that result in fossil fuel or biogenic emissions reductions or removals. These would need to be reported separately from scope 1, 2, and/or 3 emissions. 

Data Exclusions 

CARB has included proposed language on allowing for the exclusion of GHG emissions sources, activities, scope 3 categories or other information. This would be acceptable so long as the omission, misstatement, or obscuring could not be reasonably expected to influence the decisions, assessments, or understanding of users of the disclosure. Companies are directed to assess exclusions using both quantitative and qualitative factors. If a company chose to exclude data, they would be required to explain and disclose the basis for all exclusions. For each exclusion, the company would also need to disclose an estimate of the emission magnitude of the exclusion, if quantifiable.  

Notifying CARB of Changes to Methodologies 

Reporting companies would need to disclose to CARB any changes to GHG quantification or accounting methods relative to the previous reporting year or during the current reporting period. They would also need to disclose the reasons for those changes and consider if these changes would meet recalculation requirements. 

Recalculation of Previous Year Data 

If a reporting company experiences a change in GHG emissions from changes to organizational boundaries, quantification methods, data sources, emission factors, or corporate structure they would need to assess whether the cumulative effect of the changes would result in a 5% or greater change in total GHG emissions for that base year, where the base year is the first reporting year. If this threshold is met, emissions would need to be recalculated for all affected previous reporting years with the updated emission data being disclosed in the next annual emissions report, alongside a description of the changes leading to the recalculation.  

Supplemental Information 

Reporting companies may optionally disclose any additional information that adds context to their emission disclosures beyond what is already required to be reported. This information would be reported as a separate section in company disclosures.  

Lastly, CARB has indicated that they are exploring the inclusion of a requirement related to the GHGP recommendation around prioritizing primary data over secondary data. CARB is seeking feedback on how to best implement this recommendation.  

Scope 2 Reporting Requirements 

In addition to the disclosure of gross emissions in CO₂e, CARB has proposed additional reporting requirements for scope 2 emissions. This would include disclosing: 

• emissions in CO₂e by source type (e.g. electricity, steam, heating, and cooling) 
• emissions by GHG including carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃) 
• emissions using both market-based and location-based methods 

Scope 3 Reporting Requirements 

Following their March workshop, where CARB outlined three potential approaches for phased scope 3 reporting, CARB is proposing the category phase-in approach. In 2027, reporting companies would be required to disclose emissions for the following five categories: 

• Category 1: Purchased goods and services 

• Category 3: Fuel and energy related activities 

• Category 5: Waste generated during operations 

• Category 6: Business travel 

• Category 7: Employee commuting 

Companies may voluntarily report the additional ten scope 3 categories beginning in 2027 as well.  

CARB has not shared a proposed timeline or additional details on when additional scope 3 categories would be added to the reporting requirements, or which scope 3 categories would be phased in first.  

For each category of emissions that is being disclosed, companies would need to include: 

• the name and number of the category, as well as a description of the activities included
• quantification and accounting methods and the data types used
• the sum of GHG emission during the reporting period in metric tons of CO₂e
• Explanation of any emissions excluded
• the percent of emissions calculated using primary data obtained from suppliers or other members of the value chain

Assurance Requirements 

CARB confirmed the expectation that limited assurance would be required beginning in 2027 for scope 1 and scope 2 emissions, as well as biogenic CO₂ emissions. They also confirmed that assurance performed at a reasonable level would satisfy the requirements as well. CARB’s list of proposed acceptable assurance standards remained the same as shared in previous workshops, which includes: 

• AA1000 Assurance Standard (AA1000AS v3) 

• American Institute of Certified Public Accountants (AICPA AT-C Section 210) 

• International Standard on Assurance Engagements (ISAE) 3410 applied in conjunction with ISAE 3000 (Revised), for engagements commencing prior to December 15, 2026 

• International Standard on Sustainability Assurance (ISSA) 5000 for engagements commencing on or after December 15, 2026 

• International Organization for Standardization (ISO) 14064-3:2019 (with additional accreditation requirements) 

CARB also clarified expectations for what would be required as part of an assurance report. Assurance providers would need to issue a written report that:  

• Identifies the assurance standard applied and the level of assurance provided  

• Identifies the scope 1 and scope 2 emission covered by the engagement  

• States the assurance provider’s conclusion 

• Identifies the legal name of the organization that conducted the assurance engagement and contact information for the assurance provider including email, telephone number, and business address, and  

• States the date the assurance engagement was completed  

Exemptions 

CARB’s initial regulation approved by the Board in February 2026 included an exemption for insurance companies from 2026 GHG emissions reporting given existing reporting requirements for the California Department of Insurance (CDI). CARB was then directed by the Board to further investigate the alignment between CDI requirements and disclosures required under SB 253. This investigation found that CDI reporting may not satisfy SB 253 reporting requirements starting in 2027 as it does not include scope 3 or assurance requirements. Based on these findings, CARB is proposing that, beginning in 2027, insurance entities may submit the same report for both the CDI and SB 253 requirements, provided all the requirements included in CARB’s implementing regulation are met. If a company’s CDI report does not address all CARB requirements, they would need to supplement their report with the remaining required information.  

What Does This Mean for You? 

Deadlines and requirements are coming fast, but there’s still time to prepare. Here’s how to stay ahead:  

Stay in the know: Join the California Climate Disclosures Hub (SB 253 | SB 261) LinkedIn Group where the latest updates are posted. 

Assess your Readiness: Review the proposed requirements shared by CARB and assess your organization’s readiness to comply. 

Contact us for support: Our team can help you navigate requirements, design reporting strategies, and ensure compliance. Contact us at california@agendi.co or sign up for a free 30-minute discovery call. 

Dates to Know

• November 10, 2027: Proposed deadline for reporting under the proposed requirements outlined by CARB in their July 21^st workshop 

Additionally, CARB will be hosting a series of sector-specific listening sessions to gather feedback. Sign up for your relevant session here. Session schedule, below: 

• Aug 5, 2026: Data Users & Public Interest Stakeholders  

• Aug 12, 2026: Manufacturing, Industrial, Fuel & Life Sciences  

• Aug 19, 2026: Agriculture, Food, Beverage & Forestry 

• Aug 26, 2026: Energy, Utilities, Transportation, Logistics & Waste Management  

• Sep 2, 2026: Retail, Consumer Goods, Technology & Commercial Services  

• Sep 9, 2026: Banking, Finance & Insurance 

Stay Ahead of California Climate Rules  

These evolving requirements can feel complex, but early action reduces compliance risk. Need help preparing for SB 253 or SB 261? Get in touch with our team via california@agendi.co and book a 30-minute discovery call.