Scope 3 Supplier Data: What the GHG Protocol Revision Means for Your Supply Chain

For years, Scope 3 supplier data reporting lived in a gray zone. The 2011 GHG Protocol told companies to report all Scope 3 emissions. However, it gave little guidance on what that meant. As a result, most companies filled the gap with spend-based estimates. They treated it as done.

That is changing. Moreover, the Phase 1 Progress Update sets clear, defined rules. Coverage floors. Data quality tiers. Check labels. Each one hits buying teams directly.

This post breaks down the key proposed revisions and what to do now. If you’re building a supplier audit program, these revisions define what it must cover. You can also explore Certainty’s platform features for Scope 3 data workflows.

Why the March 2026 Update Matters Now

The Phase 1 update is a draft — not a final rule. However, that is not a reason to wait. Also, the Working Group held 42 meetings since September 2024. Indeed, the course is set. Final standards are due in 2027. If you start now, you’ll be ready when they hit.

There is also a policy context to keep in mind. First, the SEC’s climate rule — which never covered Scope 3 — has been dropped. Meanwhile, the EU Omnibus I cut CSRD scope to roughly 5,000 firms. Specifically, these are firms with more than 1,000 staff and €450 million in yearly sales. And California’s SB 253 requires Scope 3 reports starting in 2027.

So legal pressure is easing for now. However, the GHG Protocol changes are setting the standard. Indeed, every serious supply chain will follow suit. That includes programs driven by client deals and sector rules. Still, knowing these revisions is useful prep.

The 95% Coverage Requirement (Revision B1)

Revision B1 sets a hard floor: firms must cover at least 95% of their Scope 3 emissions. The rule caps any gaps at 5%. Also, firms must back each gap with data. For example, a hotspot study is one way to do this. Before B1, the standard used vague language. Now there is a clear, hard rule. Indeed, that’s a real shift.

For supply chain teams, this hits hardest in Category 1: Purchased Goods and Services. Also, firms that cut tail-spend suppliers must bring them in. Or they must prove the excluded share falls under 5%. That is a far higher bar than most teams now clear.

As a result, leaders should run a hotspot study against their current stock now. Don’t wait for the final rule. The study will show coverage gaps — and give you time to close them.

Data Quality Tiers and Reporting (Revision A1)

Revision A1 makes data quality visible in public reports for the first time. In detail, firms must show what share of their Scope 3 total comes from each tier. The tiers include primary supplier data, usage-based data, and spend-based proxies. Also, a fifth tier for direct data is under study.

Today, most Scope 3 reports mix data sources without labels. A single figure might combine real supplier data, industry means, and spend-based proxies. Under A1, that mix gets clear. Therefore, readers can see the quality behind each number.

Also, the standard will tag spend-based proxies as the lowest tier. Notably, that creates clear pressure to shift toward primary supplier data. According to industry guidance on Scope 3, value chain emissions top 70% of most carbon totals. That makes supplier data the top challenge in most GHG work. Yet most firms still rely on proxies.

Setting data quality goals (Revisions A6 and A7)

Two linked revisions reinforce A1. First, Revision A6 asks firms to set data goals. These set the target share of primary data. Then, Revision A7 asks for yearly data targets.

Therefore, these create a loop of steady progress. It’s not enough to report one number. Firms must show their supplier data program is getting better. This means building systems to track it.

Verification Disclosure (Revision A2)

Revision A2 closes a gap that auditors have flagged for years. Before this, firms filed Scope 3 numbers with no check label. The proposed change asks firms to label their data in one of three ways. They must also share that label publicly.

• Verified — a third party checked all Scope 3 emissions
• Partly verified — a third party checked some but not all
• Not verified — no third-party check has been done

As the Phase 1 update states, firms must share which label applies to their Scope 3 data. This puts the burden on buying teams to keep supplier data clear and sound. Therefore, audit-ready records are no longer a nice-to-have. They become the base for a label on public reports.

Supplier Data Rules (Revision A8)

Revision A8 closes a loophole that has hurt Scope 3 data quality for years. Put simply: you can no longer take a large supplier’s output and split your share by spend. The new rule states that the standard now limits this to single-industry firms only. The standard bars mixed-industry firms.

In short, A8 cuts off that path for large, mixed suppliers. Also, this affects teams sourcing from big industrial, chemical, or logistics firms. Therefore, those ties will need new data: product-level, usage-based, or site-specific. See how a supplier compliance platform handles this at scale.

What This Means for Supply Chain Teams Collecting Scope 3 Supplier Data

Taken together, these revisions send one clear message: vague, proxy-heavy Scope 3 reporting is ending. The new standard rewards teams that collect real data. Moreover, it harms those that don’t — through public labels. In short, this is a signal to buyers and markets.

For buying teams, this creates four clear problems to solve.

• Coverage gaps. The 95% floor means excluded groups must come into scope or be justified.
• Data quality tracking. A1 needs you to know — by group and supplier — what tier of data each number uses. That’s not possible without a system for logging data sources.
• Supplier method review. A8 means teams must review methods using firm-level data from large, diverse suppliers.
• Audit-ready records. A2 labels only work if the base data is documented, clear, and consistent year over year.

According to Carbon Direct’s analysis, final standards are due in 2027. If all goes to plan, full use could follow in 2028. That window is shorter than it sounds. Yet building a supplier program takes time. Tracking data quality adds more, mainly across a large chain.

Practical Steps to Get Ahead

The Phase 1 update is not yet final. However, the proposed revisions are clear enough to act on today. Here is where to start.

• Map your coverage. Find which Scope 3 categories and suppliers are in your report. Then, run a hotspot study to check whether you clear the 95% floor — or document the gap.
• Audit your data by tier. For each category, find the data type driving the number. Notably, this baseline is required under A1 and for yearly targets under A6 and A7.
• Review supplier methods. Find any suppliers where you use company-level data from a large mixed-industry firm. Those methods will be cut under A8. Therefore, plan the shift to product-level or site-level data now.
• Build a supplier data program. Specifically, start with Category 1 suppliers. Then, focus on your highest-spend and highest-emission partners. A simple form and workflow is the baseline — not a one-off email.
• Create a clear record trail. Even before formal third-party review, make sure supplier data is dated, traceable, and in a set format. Finally, the A2 label requires clear proof — not just a reported number.
• Track progress each year. Since A7 needs yearly targets, you need a baseline from the start. Build that tracking into your supplier program from day one.

The GHG Protocol’s update process is still ongoing. Also, public comment on Phase 1 has not yet opened. Still, the course is set. When standards hit, teams that build data systems now will have a clear edge.

You might also be interested in:

Frequently Asked Questions (FAQs)

What is the GHG Protocol Phase 1 Progress Update?

The GHG Protocol Scope 3 Phase 1 Progress Update was published March 31, 2026. It’s the first big proposed update since 2011. It covers draft changes on data quality, verification, supplier rules, and coverage. Importantly, it’s not a final standard. However, it sets the direction for the final update expected in 2027.

What does the 95% coverage requirement mean for supply chain teams?

Proposed Revision B1 requires companies to cover at least 95% of their Scope 3 emissions. Any excluded share must be capped at 5% and justified with data. For supply chain teams, this means tail-spend suppliers that were left out must be included. Alternatively, they must be formally shown to fall below the 5% threshold.

What are the Scope 3 data quality tiers under Revision A1?

Revision A1 requires companies to break their Scope 3 figures down by data type. The tiers include primary supplier data (best quality), usage-based data, and spend-based proxies (lowest quality). The working group is still reviewing a fifth tier for measured data. The goal is to make data quality visible — and give companies a clear reason to improve.

Why does Revision A8 restrict supplier data methods?

Revision A8 addresses a long-standing data problem. Many firms have allocated a share of a large supplier’s total emissions based on spend ratios. For diverse suppliers, this produces unreliable numbers. A8 limits company-level allocation to single-industry suppliers only. Firms sourcing from diverse suppliers must get product-level or site-level data instead.

Is Scope 3 reporting now mandatory?

Mandatory rules depend on where you operate and your company size. Here’s what applies by region. The EU’s CSRD (ESRS E1) requires Scope 3 reports for in-scope firms — now narrowed to roughly 5,000 under Omnibus I. California SB 253 requires Scope 3 reports starting in 2027 for firms with over $1 billion in annual sales. The SEC’s climate rule has been dropped. Also, Scope 3 reports are now required by many customers, investors, and sector groups.

What does Revision A2 require for verification disclosure?

Revision A2 requires companies to label their Scope 3 data as Verified, Partly verified, or Not verified. Importantly, the label must be shared publicly. For procurement teams, this means supplier data needs to be documented and traceable — not just a summary in a spreadsheet.

When will the final GHG Protocol Scope 3 Standard take effect?

According to Carbon Direct’s analysis, the GHG Protocol expects to publish the final Scope 3 Standard in 2027. Notably, early adoption may be possible in 2026. Full use is expected in 2028 or later, depending on how CSRD and SBTi update their own rules.