California’s Senate Bill 253 is reshaping how large companies measure, report, and verify their climate impact. With the first Scope 1 and Scope 2 disclosure due August 10, 2026, the window to prepare is short, but the work pays off well beyond compliance. In our recent webinar, “Preparing for SB 253 with Confidence: Understanding Inventory and Assurance Requirements,” the 3R Sustainability panel walked through what the law requires, why a greenhouse gas inventory matters as a strategic tool, and how third-party assurance fits in.
Who SB 253 covers, and when
SB 253 applies to public and private U.S. companies with more than $1 billion in annual revenue that do business in California. Scope 1 and Scope 2 reporting is required by August 10, 2026, for the prior fiscal year. The bar rises from there: limited assurance over Scope 1 and 2 begins in 2027, Scope 3 reporting joins in 2027, and reasonable assurance for Scope 1 and 2 phases in by 2030.
A GHG inventory is more than a compliance exercise
A defensible inventory captures direct emissions you control (Scope 1), the energy you purchase (Scope 2), and the value chain emissions you influence (Scope 3). The most common stumbling blocks are data quality and multi-site coordination. Standardized data collection templates, clear ownership of each input, and early engagement with operations and procurement teams save weeks at the end. Done well, the inventory becomes more than a report; it uncovers efficiency opportunities, strengthens climate resilience, supports investor and customer requests, and protects your brand against rising greenwashing exposure.
Assurance doesn’t have to be intimidating
Our partner, Sustainability Assurance Services (SAS), provides third-party verification and assurance of sustainability-related data and reporting.
The growing role of third-party assurance
Assurance is moving from a nice-to-have to a business essential. SB 253 is one driver, but EcoVadis, CDP, GRESB, investors, and customers are increasingly asking for independent verification of climate data. Limited assurance, required beginning next year, is a review of processes and calculations completed largely remotely. Reasonable assurance, which begins in 2030, is a deeper examination requiring more time and resources. Even where assurance is not yet required, a pre-assurance review gives leadership confidence that a public disclosure will hold up to scrutiny.
What “good faith” really means in year one
CARB has acknowledged that perfect data is not realistic in year one and has signaled flexibility for organizations that demonstrate good-faith effort. That flexibility is not a free pass. It rewards companies that document their methodology, prioritize primary data where possible, and clearly explain where estimates or proxies were used. An assurance partner can confirm your disclosure meets the good-faith threshold before you submit.
Where to start
For organizations that have not begun, the next 90 days matter. Build organizational boundaries, identify data owners, gather utility and fuel records, and document every assumption. For companies further along, a pre-assurance review is the highest-leverage step before August. Either way, 3R Sustainability, along with our assurance partner, Sustainability Assurance Services, is ready to help you turn the SB 253 deadline into long-term business value, across responsibility, resilience, and results.
Want to talk through your SB 253 readiness? Contact the 3R team or watch the full webinar recording.