A company that replaces industry averages with supplier figures can find that its Scope 3 starting point has moved, and the progress it has been reporting moves with it. Better data is worth having, but leadership needs to know how much of any change reflects the accounting and how much reflects emissions that actually fell.
In Scope 3 accounting, the baseline is the base-year estimate of value chain emissions that reduction targets are measured against. Under the Greenhouse Gas Protocol's Corporate Standard, companies must keep a policy for recalculating it. Changes in calculation method or improvements in the accuracy of emission factors or activity data can require a recalculation, alongside structural changes and significant errors. Companies are expected to state any significance threshold and apply the policy consistently, whether a correction pushes the baseline up or down. Changes that reflect real shifts in emissions, such as a supplier cutting its fuel use, are not a reason to recalculate.
More Scope 3 figures are now sitting in front of auditors and regulators. Chartered Accountants Australia and New Zealand, Purpose Bureau and Monash University published a review on October 14 of 154 companies in Australia's first mandatory climate reporting group. It found that 54 disclosed Scope 3 emissions even though they had a first-year exemption. Twenty-five of them had that information independently assured. Once a number has been assured and published, a later reset to its baseline is no longer an internal housekeeping matter.
Standard setters are heading the same way. A March 2026 progress update on the GHG Protocol's Scope 3 revision is labeled draft and subject to change. It proposes that companies break out their Scope 3 totals by data type or calculation method, with spend-based estimates shown separately. The update also floats a requirement to say whether the figures were verified by a third party. The same document notes that data type is not, by itself, a measure of quality. Both proposals push in the direction that turns Scope 3 disclosure into evidence auditors can test line by line.
Take a manufacturer that first estimated the emissions from its purchased materials using spending data and industry averages. A few years later, suppliers send figures showing those same historical purchases produced less than the original estimate. If this year's emissions are compared with the old estimate, progress looks larger than it does against a baseline recalculated with the supplier figures. The gap between the two is a corrected starting point, not a cut in emissions.
The reverse can happen too. Supplier figures that come in higher than the average can make emissions appear to rise even though purchasing volumes and supplier operations barely changed. Finance leaders will recognize the pattern from restated accounts. Neither version alters what suppliers physically emitted, but picking the wrong comparison can overstate or understate real progress.
Supplier responses mark the start of a quality check. The GHG Protocol's Scope 3 technical guidance warns that data collected from a supplier may be less accurate than industry-average data for a particular product. Allocating a supplier's total emissions across the products it sells adds considerable uncertainty as well, the guidance says. A figure arriving from a supplier does not, on its own, make it the better number.
One practical control is to ask the sustainability team to document why a replacement figure is more representative before its effect reaches reported performance. That record should cover the product purchased, the plant that made it, the reporting period and the emissions sources included. The same scrutiny belongs on revisions that raise the total, which is also what the standard's consistency requirement asks for. Skipping that step is how inventories end up with figures that cannot be compared across years, even within one company.
Many suppliers can provide current figures but have nothing comparable for the base year. Applying today's emissions intensity to purchases made years earlier is tempting and can backfire. If the supplier has since upgraded its process, that shortcut erases an improvement the buyer is trying to measure, and under the standard that improvement is a real change, not a methodology fix.
Estimating past emissions in this way, known as back-casting, reduces the reliability of a base year, the Corporate Standard acknowledges. Management should expect a written account of the historical assumptions, the evidence behind them and the limits on comparison before signing off on a revised baseline.
Raising the share of emissions backed by representative supplier data is a data-quality achievement. Showing lower emissions on a comparable basis is a performance achievement. The progress update's proposed specificity metrics point toward reporting the first separately, and executive scorecards can do the same now.
Good reconciliations walk from the previously reported baseline to the revised baseline and then to current emissions. Along the way they separate the effects of purchasing volumes, product mix, supplier performance, method changes and corrected information, and they leave any effect that cannot be isolated visible as a limitation. As Scope 3 figures move into regulated reports, the legal exposure from unsupported claims grows with them, and a documented trail is the strongest defense a company has.
The GHG Protocol's consolidated draft is expected out for public consultation around the second quarter of 2027. If the disaggregation proposal survives, every reported Scope 3 total will carry a breakdown of how it was calculated, and a baseline reset will show up in the data itself. How far the final standard goes on verification and specificity targets is still open, and the consultation is where companies will get to argue it.
