Most carbon numbers are a guess with a decimal point
Only seven companies in a hundred measure all three scopes, and the share is falling. The missing one is the one that matters.
Seven per cent. That is how many large companies comprehensively report all three emission scopes, according to the 2025 BCG and CO2 AI Climate Survey. It was 9% in 2024 and 10% in 2023, so the number is going backwards.
The number is not surprising on its own. What makes it serious is which scope is missing. Scope 1 is your own operations and Scope 2 is the energy you buy — between them, usually a small minority of your footprint. Scope 3, everything upstream and downstream in your supply chain, is routinely more than 90% of the total.
So the shape of the average corporate carbon disclosure is this: a small, carefully measured piece, bolted onto a very large guess, published as a single figure with a decimal point.
Why the guess persists
Ask companies what is stopping them and the answer is consistent. The barrier is not modelling, software or budget. It is that the data sits inside other companies, and those companies have not been asked for it before.
This is a coordination problem dressed up as a technical one. A large buyer needs emissions data from four hundred suppliers. Those suppliers have never been asked for it, do not have a sustainability function, and receive the request as a spreadsheet with terminology they have no reason to know. Most do not respond. Of those who do, many return numbers that were themselves estimated.
The buyer then averages the responses, applies a spend-based factor to the gaps, and publishes a total. Every step is defensible. The result is not measurement.
What changes when someone checks
An estimate is a perfectly reasonable thing to publish, right up until the moment a figure carries consequences. That moment has arrived from three directions at once.
- Assurance requirements are tightening, and a verifier's job is to trace a number to its source. An estimate cannot be traced.
- Carbon border taxes convert emissions into landed cost, which means a buyer's procurement team now has a financial reason to interrogate your figure.
- Lenders and investors increasingly price transition risk, and a footprint that cannot be substantiated is treated as the worst plausible case.
The honest version
The first thing a serious carbon system should do is tell you which of your numbers are measured and which are estimated, and refuse to blur the two. That makes the first report look worse than the polished one you might have published otherwise.
It is also the only version that survives contact with someone whose job is to check.