This is an independent summary, not legal advice. Assurance requirements are still being developed, and CARB's positions have changed over time. Confirm the current position with CARB and qualified counsel.
What the statute says
According to the text of SB 253 (Health and Safety Code section 38532), reported emissions are to be subject to third-party assurance on a phased schedule:
- Scope 1 and Scope 2: limited assurance beginning in 2026, and reasonable assurance beginning in 2030.
- Scope 3: limited assurance beginning in 2030, with CARB to establish requirements.
The statute describes the assurance provider as an independent entity with significant experience measuring, analyzing, reporting or attesting to GHG emissions. Confirm the exact wording of the independence and experience language on the official statute page.
CARB's position on the first report
CARB's March 2026 workshop slides state that limited assurance is not required for the 2026 report under CARB's first-year enforcement discretion. CARB's earlier FAQ (July 2025) had said limited assurance starts in 2026 under the statute. The difference shows that CARB's guidance has evolved, so check its current pages.
Proposed only: 2027 and later
CARB staff presentations from March and July 2026 propose limited assurance of Scope 1 and Scope 2 beginning with 2027 reports, performed by an independent third party using one of a list of accepted standards. The standards named in CARB's slides are:
- AA1000AS v3
- AICPA AT-C 210
- ISAE 3410, used together with ISAE 3000 (Revised)
- ISSA 5000, for engagements commencing on or after December 15, 2026
- ISO 14064-3:2019, which CARB's slides describe as carrying additional accreditation conditions
These are proposals, not adopted rules.
What we could not confirm
We found no adopted CARB rule on assurance-provider qualifications or accreditation, and no CARB-approved list of assurance providers. Any vendor that describes itself as "CARB approved" or as guaranteeing compliance should be asked for a source.
How this directory treats assurance providers
SB253 Vendors lists organizations that state they offer verification or assurance services. A listing is not an endorsement, approval, certification or ranking. Where we show accreditation evidence, it is as displayed on the cited source page on the date shown, and you should confirm it with the accrediting body and the provider. See our methodology page for how listings are compiled.