Who Regulates Carbon Emissions Reporting — and Why It Ends Up in Your Inbox — CarbonSig

Last quarter, your biggest customer sent you a sustainability questionnaire. This quarter, a second customer sent one too. Same questions. Different format. Somewhere behind both of them are four groups you should know.

Here is your map.

The rule-makers

Governments write the rules that force large companies to measure and report their carbon emissions.

The EU leads. Its supply chain reporting law (CSRD) requires major companies to disclose emissions data — including emissions from their suppliers. California is close behind: its climate disclosure law (SB 253) requires companies with over $1 billion in revenue to report emissions starting in 2026. The UK adopted its own standards in 2026, with mandatory reporting in 2027. And the global baseline-setter (ISSB) is building the framework that ties it all together. Over 30 countries have adopted or are adopting it.

If you are a supplier to any company touched by these rules, the paperwork flows downhill to you.

The scoreboards

Once the rules exist, companies need somewhere to report — and someone to keep score.

CDP (formerly the Carbon Disclosure Project) is where companies report. Over 22,100 disclosed environmental data through CDP in 2025. GRI (the Global Reporting Initiative) sets the standards for how they report. And SBTi (the Science Based Targets initiative) defines what companies commit to — over 10,000 now have science-based climate targets.

These organizations do not make the rules. They keep score. And their scores follow you. When your customer checks your CDP rating before renewing a contract, this is where that number came from.

The buyers sending questionnaires

Large companies do not just report their own emissions. Under most frameworks, they also report their supply chain’s emissions. That means they need data from you.

Apple requires over 300 suppliers to commit to renewable energy and meet strict emissions targets. Falling short can cost you the contract. Walmart invited 50,000 suppliers into its Project Gigaton program and hit its billion-ton reduction goal six years ahead of schedule. BMW, Volkswagen, and Toyota are building shared carbon accounting standards for the entire automotive supply chain.

When these companies send a sustainability questionnaire, it is not curiosity.

It is compliance.

That is the difference. They are not asking because they want to. They are asking because they have to.

The money pushing it forward

Over 5,300 investors have signed the UN’s responsible investment principles (PRI), collectively managing $128 trillion. They do not just ask companies to be environmentally responsible. They ask for specific, comparable carbon data. When a pension fund asks a public company for emissions numbers, that company turns around and asks its suppliers.

You may never meet these investors. But their requirements are the reason your customer’s questionnaire exists.

How the chain works

Regulators set the rules. Corporations comply — and to comply, they need data from their supply chain. Investors push the whole cycle forward by tying capital to disclosure. You are at the end of that chain. Not because you chose to be, but because your customers and their investors did.

“They are not asking because they want to. They are asking because they have to.”

A reasonable objection — and why it doesn’t hold

Critics of this cascade argue that small suppliers are bearing reporting cost imposed by laws that were not designed for them — that the burden is regulatory creep dressed up as compliance. However, the cascade is not a bug. It is the explicit design choice in CSRD Article 19a and in California’s SB 253 §38532: large emitters cannot reduce what they cannot measure across their value chain, and the value chain is, definitionally, their suppliers. Some would say the right response is to wait until thresholds change. The data on enforcement timelines argues the opposite — the questionnaires are arriving in 2026, not 2028.

What comes next

Now you know the players. In Part 5, we break down the glossary — plain-English definitions for every term these organizations use.

Originally published at https://carbonsig.com on May 7, 2026.

Sources

1. Sustainability Reporting Pulse 2026 (CDP supply chain programme dataset) — median supplier now receives ≥2 customer sustainability questionnaires per year. cdp.net/supply-chain-data
2. Corporate Sustainability Reporting Directive (EU) 2022/2464, Articles 19a–19c — value-chain emissions disclosure. eur-lex.europa.eu/eli/dir/2022/2464
3. ISSB IFRS S2 Climate-related Disclosures — global baseline standard adopted Q1 2026 by 30+ jurisdictions. ifrs.org/issued-standards/ifrs-sustainability-standards-navigator/ifrs-s2-climate-related-disclosures
4. California SB 253 (Climate Corporate Data Accountability Act), §38532 — Scope 3 reporting requirement. leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202320240SB253

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If you’re starting on your carbon accounting journey, the next piece in our Getting Started series — Carbon Accounting on a Shoestring — walks through producing a defensible first carbon number from data you already have. Read it at carbonsig.com