California has expanded its Mandatory Reporting Regulation for greenhouse gas emissions to cover additional industrial processes and specified cement and hydrogen businesses. The California Air Resources Board's final amendments took effect September 1 after approval by the Office of Administrative Law.

The immediate obligation is narrow but important. An existing California entity newly covered because it uses one of the added industrial processes and exceeds the 10,000-metric-ton carbon dioxide equivalent threshold must notify CARB's executive officer within 90 days of the rule's effective date. November 30, 2026 is 90 calendar days after September 1; a business should confirm CARB's deadline-counting and filing instructions for its circumstances. An entity that starts one of those processes later has 90 days from when the process begins.

Most of the amended regulation applies to 2027 data reported in 2028. Existing reporters also have changes to prepare for when they submit 2026 data in 2027, including revised electric-power, product-data, and verification provisions.

Which additional industrial entities are covered

The new section 95101(a)(1)(G) applies to a California reporting entity that is subject to any of 23 listed federal greenhouse gas reporting subparts and emits more than 10,000 metric tons of carbon dioxide equivalent from carbon dioxide, methane, or nitrous oxide.

The list reaches a broad set of federal reporting categories, including adipic acid, aluminum, ammonia, electronics manufacturing, ferroalloy, fluorinated gas, petrochemical, phosphoric acid, silicon carbide, soda ash, titanium dioxide, underground coal mines, zinc, industrial wastewater, and industrial waste landfills. A business must use the lettered subparts in the final California text, not a general industry description, to determine whether the provision reaches its process.

Applicability depends on the reporting entity, its process, the federal subpart, and its emissions calculation. The final California text says the 10,000-metric-ton comparison includes stationary-combustion and process emissions of carbon dioxide, methane, and nitrous oxide, but it allows vented and fugitive emissions to be excluded from that particular threshold calculation. A facility with total emissions above the separate 25,000-metric-ton threshold may be ineligible for abbreviated reporting and subject to the full reporting and verification requirements.

The 90-day notice provision also reaches an operator eligible for abbreviated reporting. The final order does not prescribe a new public notice form in the text, so a potentially covered operator should confirm the required submission route with CARB rather than relying on a generic filing.

New cement-import reporting starts with 2027 data

The amendments add a reporting category for an importer whose emissions associated with cement or clinker brought into California equal or exceed 10,000 metric tons of carbon dioxide equivalent in a calendar year. Section 95126 says those requirements begin with data year 2027.

A covered importer must report annual emissions tied to cement and clinker from each manufacturing facility and the total across all facilities. The report also requires quantities imported, specified component information when known, the sources and methods used for a facility-specific emissions intensity, electricity used to produce the cement when available, and the manufacturing facility's name and address when known.

If a manufacturing facility's emissions and production are not known, the final rule supplies a default cement emissions intensity of 0.758 metric tons of carbon dioxide equivalent per short ton. Cement or clinker imported into California and then exported for use outside California is still included in the information required by section 95126.

CARB exempted the new cement-import data from the regulation's third-party verification requirement. The underlying annual report is still mandatory for a covered importer.

Hydrogen thresholds and required data

The amended rule also covers an importer that brings at least 500 metric tons of hydrogen into California during a calendar year. It separately covers an in-state plant that produces at least 500 metric tons of hydrogen using electricity during a calendar year when that plant is not already reporting under the regulation's existing hydrogen-production category.

For an in-state electric hydrogen producer, section 95127 requires electricity-consumption and emissions data, broken out between known and unknown generation sources, along with annual hydrogen production and specified monthly matching information. A covered hydrogen importer must report the imported quantity and measurement point, the producer's name and location, the production technology and operating-start date, and the associated production emissions information required by the final text.

Those hydrogen reports are not treated as covered emissions under the Cap-and-Invest program, and the new hydrogen data is exempt from third-party verification. The broader reporting obligation nevertheless applies beginning with the amended regulation's 2027 data year unless the rule specifies otherwise.

What changes for existing 2026 reports

The final timing provision makes a limited group of amendments applicable to 2026 data reported in 2027. These include revised definitions and reporting provisions for electric power entities, product-data definitions, and updated verification requirements. The default annual deadlines remain April 10 for most facilities and suppliers and June 1 for electric power entities and abbreviated reports, with verification statements due August 10 when verification applies.

This rule is separate from California's corporate climate-disclosure laws. The Mandatory Reporting Regulation is a facility, supplier, and electric-power reporting system with its own applicability thresholds and data fields. A company should not assume that an analysis of Senate Bill 253 reporting answers whether one of its facilities or imports falls within these amendments.

The September 1 effective date and November 30 notice date are recorded on Federal Weekly's compliance calendar, and the amendments are listed in the Business Rule Change Tracker.

The practical takeaway

A California business that operates one of the newly listed industrial processes should map its federal Part 98 subpart and calculate the emissions relevant to the 10,000-metric-ton threshold now. If the entity was newly covered on September 1, it should contact CARB promptly to confirm how to submit the notice due within the 90-day period.

Cement importers should identify the manufacturing source of imported cement and clinker, preserve quantities and emissions-intensity support, and prepare to collect the new fields for data year 2027. Hydrogen importers and electric hydrogen producers should test the 500-metric-ton threshold and map production, electricity, measurement-point, sourcing, and emissions data before that data year begins. Existing MRR reporters should also update their 2026 reporting and verification workpapers for the provisions that apply in 2027.