California's Landmark Corporate Climate Disclosure Law Takes Effect, Mandating Scope 3 Emissions Reporting

The era of voluntary corporate climate reporting in the United States is officially ending. California's landmark Climate Corporate Data Accountability Act, widely known as SB 253, has entered its practical implementation phase, fundamentally altering the national regulatory landscape.[2]

SB 253 requires any United States-based company doing business in California with more than $1 billion in annual revenue to publicly disclose its greenhouse gas emissions. Because the revenue threshold applies to the entire company and the geographic trigger is merely "doing business" in the state, the law captures thousands of corporations nationwide, establishing a de facto national standard.

The most transformative element of the legislation is its mandate for Scope 3 emissions reporting. While Scope 1 covers direct operational emissions and Scope 2 covers indirect emissions from purchased energy, Scope 3 encompasses the entirety of a company's indirect value chain. This includes emissions from supply chains, business travel, waste generation, and the end-consumer use of products.

Scope 3 emissions frequently account for the vast majority of a corporation's carbon footprint, yet they remain the most difficult to track and calculate because they occur outside the company's direct control.[2]

While the law is currently taking effect, the California Air Resources Board (CARB) recently adjusted the immediate timeline. On June 24, 2026, CARB announced a three-month deferral for the initial Scope 1 and Scope 2 reporting deadline, shifting it from August 10 to November 10, 2026.[1]

This deferral is intended to provide reporting entities with additional time to comply with forthcoming clarifying amendments to the initial regulations. However, regulators have emphasized that the 2026 reporting year remains firmly in place, and companies are expected to submit their data this fall.[1]

The timeline for Scope 3 disclosures remains set for 2027. In preparation, CARB recently held public workshops to outline three potential regulatory options for how the Scope 3 rollout will be structured.

The first option, "Broad Applicability," would require companies to report on all 15 recognized Scope 3 categories beginning in 2027, though they could exclude categories deemed mathematically insignificant, provided they offer an appropriate explanation.

The second option, "Sectoral Phase-In," would initially require Scope 3 reporting only from the transportation and industrial sectors. These sectors account for roughly 60% of California's emissions and face the greatest transition risks, making them a priority for regulators.

The third option, "Category Phase-In," would require all covered companies to begin by reporting only on the most commonly disclosed Scope 3 categories, such as business travel, employee commuting, and fuel-related activities, before expanding to the full value chain.

Alongside SB 253, California passed a companion law, SB 261, which requires companies with over $500 million in revenue to publish biennial reports detailing their climate-related financial risks.

However, the enforcement of SB 261 is currently paused due to an injunction from the U.S. Ninth Circuit Court of Appeals amid ongoing litigation led by business groups. Despite this legal challenge to the risk-reporting law, SB 253's emissions reporting mandate remains fully in effect.[1]

To ensure data accuracy, SB 253 incorporates phased third-party assurance requirements. No assurance is required for the initial 2026 filings. However, "limited assurance" becomes mandatory for Scope 1 and 2 emissions starting in 2027, eventually upgrading to "reasonable assurance"—a much higher audit standard—by 2030.

CARB will decide separately in 2027 whether third-party assurance will eventually be required for Scope 3 emissions, acknowledging the inherent complexities in auditing external supply chain data.[2]

Enforcement mechanisms under the law are substantial. CARB is authorized to pursue civil penalties of up to $500,000 per year for non-compliance with SB 253.

To ease the transition, the legislation includes a safe harbor provision for Scope 3 reporting. Until 2030, companies will not face penalties for misstatements in their Scope 3 disclosures, provided the reports are made with a reasonable basis and disclosed in good faith.

For the first reporting cycle in 2026, CARB has indicated it will exercise enforcement discretion, expecting companies to submit the data they currently have on hand. If a company was not actively collecting emissions data prior to the enforcement notices, it may submit a short statement explaining the non-collection for 2026, though a full inventory will be expected in 2027.[1]

Sustainability and governance experts advise that companies should not view the 2026 grace period as a reason to delay. Instead, organizations are urged to use the initial filing to pressure-test their accounting methodologies, identify governance gaps, and align their data collection systems before mandatory assurance kicks in.[2]

Many multinational corporations are currently mapping California's requirements against other global frameworks, such as the European Union's Corporate Sustainability Reporting Directive (CSRD) and the SEC's federal climate rules, to streamline their compliance efforts.

As the November 10 deadline approaches, the implementation of SB 253 marks a permanent shift in corporate transparency. By mandating comprehensive value chain disclosures, California is forcing the global market to quantify and confront the true carbon footprint of modern commerce.[2]