Companies heading into their first required Scope 3 reports are about to ask suppliers for numbers that, in most cases, nobody has measured. The buyers that get usable answers back will be the ones that narrow their requests to the suppliers and data points that matter.
Scope 3 covers the emissions in a company's value chain, from the goods it buys to how its products are used, and most of those emissions sit on other companies' books. California is the first large deadline. Its Air Resources Board (CARB) covers companies that do business in the state with more than $1 billion in revenue. Under guidance issued in September, they must report Scope 1 and 2 emissions by November 10. The state's Office of Administrative Law approved those first-year rules on October 12, a law firm summary notes. Scope 3 follows in the 2027 reporting cycle, under a second rulemaking CARB has not yet completed.
At a July 21 workshop, CARB staff previewed an initial Scope 3 requirement covering five categories, another law firm's account of the session shows. They are purchased goods and services, fuel- and energy-related activities, waste from operations, business travel and employee commuting. The remaining categories under the Greenhouse Gas Protocol would stay voluntary for now.
Purchased goods and services is where supplier data carries the most weight, because those emissions are generated in suppliers' plants and farms. Fuel- and energy-related activities ties the reporting calendar to this winter. It counts the upstream emissions of the fuel and power a company buys, so the same cold-weather fuel use that drives energy budgets also flows into the inventory. Companies finishing their November 10 Scope 1 and 2 filings already hold much of that energy data.
A 2026 Carbon Action Report from EcoVadis, a company that sells sustainability ratings of suppliers, and the consultancy Kearney shows how wide the gap is. Drawing on 56,000 companies EcoVadis rated on carbon over the past year, it finds that only 4% report primary Scope 3 data. Companies relying on weaker data may be underestimating their Scope 3 emissions by about 2.7 times, the report estimates. Those with verified Scope 1 and 2 figures are eight times more likely to engage suppliers on carbon.
Most inventories today fill the gap with industry averages and spend-based estimates. Those are acceptable starting points, but if the report's estimate holds, real supplier figures could push some totals up once they arrive. Supplier readiness has lagged behind buyer demand for some time, and the 2026 figures give little sign of a turnaround.
Europe has moved in the other direction on requests to smaller firms. The Council gave final approval in February to the Omnibus package that narrows the Corporate Sustainability Reporting Directive (CSRD) to companies with more than 1,000 employees that also clear a turnover threshold. In July the European Commission adopted revised reporting standards that cut mandatory datapoints by more than 60%, along with a voluntary standard for smaller companies outside the directive.
That voluntary standard carries a value chain cap. Companies covered by the CSRD cannot require their value chain partners to provide more information than the standard covers. For multinationals whose European entities fall under the directive, the cap limits what those entities can require of smaller suppliers. Mid-size suppliers already absorbing environmental pressure now have a firmer basis for pushing back on sprawling questionnaires. Buyers outside Europe can use the same template as a ready model for keeping requests proportionate.
Concentration works in a buyer's favor. Across the EcoVadis network, 10% of companies account for 95% of emissions. A supplier program that starts with the largest emitters in its own spend, instead of surveying everyone, puts limited staff time where the numbers move.
The first request does not have to be a finished product footprint. Metered electricity, fuel purchases and production volumes are records suppliers already keep for billing and operations, and those figures can be turned into credible estimates. Contracts renewing over the next year are a natural place to add data delivery dates and formats, along with any support the buyer is willing to fund.
For suppliers, the crunch cuts both ways. A supplier that can hand over verified energy and emissions figures saves its customer estimation work and a likely restatement later. As more buyers face 2027 filings with thin primary data, those suppliers have a case to make when contracts come up for renewal, and the ones still relying on averages will be competing against them.
