California's SB 253 is the only mandated corporate climate dataset arriving in the United States this year. The first deadline, 10 November 2026, has been described to me by more than one client as "the hard part". It is not. The 2026 filing is a good-faith Scope 1 and 2 submission with no assurance, in any of three formats, most of which you already publish. The hard part is that everything you submit this November becomes the baseline that limited assurance and five Scope 3 categories will be measured against in 2027. Here is how to think about the next eight weeks.
What the 2026 filing actually requires
CARB adopted its initial SB 253 and SB 261 regulation unanimously on 26 February 2026 and moved the first Scope 1 and 2 deadline from 10 August to 10 November. On 1 September it published guidance for the 2026 submittals and opened a voluntary Report Intake Platform; entities may instead email their report and contact details to CARB. Three formats are acceptable: an existing annual or sustainability report containing Scope 1 and 2 emissions, existing Scope 1 and 2 data already reported to another programme or voluntary initiative, or CARB's draft Scope 1 and 2 template. The data year is whatever you possessed as of December 2024, and no assurance is required for this cycle.
One caveat sits under all of it. The 10 November date is still contingent on the Office of Administrative Law approving the deadline amendment. Plan for 10 November; do not plan on it slipping.
The fee notice is the first enforceable touchpoint
Fee determination notices went out on 10 September, and payment is due within 60 days, with late fees. The fee is flat: annual programme cost divided by covered entities. Entities with USD 500 million to 1 billion in revenue pay the SB 261 fee only; those above USD 1 billion pay both. Two practical points. First, the intake platform doubles as the channel for supplying a billing contact, so register a contact even if you email the report. Second, if you are not sure you are a covered entity, the fee notice is the moment to establish that, because paying it is a concession that you are.
Entity-by-entity scoping is the work nobody has done
"Doing business in California" is tested entity by entity using tax concepts, but the emissions are reported on a consolidated basis. Most groups have never reconciled these two boundaries. A parent may be out of scope while two subsidiaries are in, and the emissions of a consolidated filing may not match the sum of the entities that triggered it. Decide now which entities file, whether the group files once on their behalf, and how intercompany energy purchases are eliminated. Whatever boundary you choose in November is the boundary the practitioner will test in 2027, so choose the one you can re-perform.
The 2027 cliff
At its 21 July workshop CARB previewed the 2027 framework and said formal rulemaking would follow later in 2026. The proposal limits Scope 3 to five categories, requires limited assurance on Scope 1 and 2 from 2027 through 2029 and reasonable assurance from 2030, and accepts AICPA attestation standards, ISAE 3000 and 3410 through December 2026, and ISSA 5000 after that. The Scope 3 assurance decision is deferred to 2027.
That means the assurance clock starts on FY2026 data, the data you are living through now. An operator with fragmented site-level metering, a mix of utility bills and estimates, and a market-based Scope 2 built on contracts nobody has reviewed since 2022 has three months to close the gap between the GHG inventory and the financial consolidation boundary. Pick the assurance standard in the same conversation as the auditor: AICPA AT-C and ISSA 5000 produce different evidence files, and the difference shows up in what you have to collect this year.
The legal landscape around it
SB 261, the climate-risk report, remains enjoined by the Ninth Circuit's November 2025 order; the court heard argument in January 2026 and has not ruled. SB 253 is live. Federally, the SEC's proposed rescission of its 2024 climate rule is still in rulemaking after more than 19,000 comments, and the 2010 interpretive guidance continues to govern 10-K disclosure of material climate risk. No other state has an enacted mandate: New York's bill died in the Assembly in June and Illinois's sits in committee. If you are looking for the rule that will make you report in the US, this is it.
What to do before 10 November
- Confirm covered-entity status per legal entity and reconcile it to the consolidation boundary you will report on.
- Choose the 2026 format that matches data you can re-perform: existing report, existing programme data, or CARB's template. Do not submit a number you could not defend under limited assurance.
- Register the billing contact on the intake platform; calendar the fee due date (60 days from your 10 September notice).
- Inventory your Scope 2 contracts and emission-factor sources now; the market-based method is where 2027 assurance findings will cluster.
- Start the Scope 3 screen for the five likely categories so the 2027 rulemaking does not catch you cold.
ESG Advising does SB 253 readiness reviews built around the 2027 assurance standard rather than the 2026 filing, because the filing is easy and the baseline is permanent.
