Carbon Accounting Check Skill

A GHG inventory fails audit (and credibility) on boundaries, factors, and data quality — rarely on arithmetic. This skill runs a structured sanity pass over an inventory so the weak points are found internally, not by an assurer or a journalist. It reviews rigor; it does not certify compliance.

What This Skill Produces

• A scope 1/2/3 boundary review with gaps and out-of-boundary items named
• A data-quality tier map (measured / calculated / estimated / proxy) per emission source
• The top emission-factor sensitivities — where a factor choice swings the total
• A year-over-year bridge separating real reduction from methodology or boundary change
• Double-counting flags and a prioritized fix list

Required Inputs

Ask for these if not provided; if the brief is thin, proceed with clearly labelled assumptions rather than refusing:

• Inventory data — emissions by scope and category, with units (tCO2e), and the reporting year
• Organizational boundary — operational control, financial control, or equity share, and which entities are in/out
• Scope 2 method(s) — location-based, market-based, or both; contractual instruments held (RECs, GOs, PPAs)
• Emission factor sources — which factor sets and vintages were used per category
• Data provenance — per major source: meter/invoice, activity-data calculation, estimate, or spend-based proxy
• Prior-year inventory (optional) — needed for the YoY bridge
• Offsets or removals held (optional) — reviewed separately, never netted

Review Framework

Walk the inventory in this order:

1. Boundary. Confirm the consolidation approach is stated and applied consistently. For scope 3, check all 15 GHG Protocol categories were screened — a category may be excluded only with a stated reason and a rough size estimate.

2. Scope 2 duality. Both market- and location-based figures should exist. Flag market-based claims without matching contractual instruments (vintage, geography, retirement).

3. Data-quality tiers. Assign each material source a tier and estimate what share of the total sits in each:

Tier	Basis	Typical uncertainty
Measured	Meters, fuel invoices, utility bills	Low
Calculated	Activity data × published factor	Low–medium
Estimated	Extrapolation, averages, occupancy models	Medium–high
Proxy	Spend-based, industry-average intensity	High — directional only

Flag any headline claim (e.g. "-12% YoY") that rests mostly on proxy-tier data.

4. Factor sensitivity. Identify the 3–5 sources where switching to an equally defensible factor set or vintage moves the total by >2%. Recompute or estimate the swing.

5. YoY bridge. Decompose the change into: activity change, factor/vintage updates, boundary changes, methodology changes, and data-quality improvements. Only the first is a real emissions trend.

6. Double-counting traps. Check the classics: fleet fuel in both scope 1 and scope 3 category 6; electricity in scope 2 and again via spend-based scope 3; parent and subsidiary both claiming the same site; RECs claimed against grid averages already lowered by those RECs; leased assets counted by both lessor and lessee.

Output Format

GHG inventory check: [organization, reporting year]

1. Summary verdict — publishable as-is / publishable with caveats / fix first, with the two or three decisive reasons.

2. Boundary review — consolidation approach, scope 3 category screening table (included / excluded + reason + size estimate), gaps.

3. Data-quality map — table of major sources × tier × share of total, with the weakest material sources called out.

4. Factor sensitivities — the top swings, each with source, alternative factor, and estimated delta.

5. YoY bridge — waterfall from prior year to current year with each driver quantified or labelled as an estimate.

6. Flags and fixes — numbered list, each with severity (blocks publication / caveat needed / improve next cycle) and a concrete fix.

Include this line in the artifact: "Verify boundary, methodology, and disclosure choices against the applicable standard (e.g. GHG Protocol, ISO 14064-1) and regulation with your compliance team and assurer."

Quality Checks

• Consolidation approach is stated and every in/out entity decision is visible
• All 15 scope 3 categories are screened; exclusions have a reason and a size estimate
• Both scope 2 methods are reported, or the absence of one is flagged
• Every material source has a data-quality tier; the share of total per tier is stated
• The YoY bridge separates real activity change from methodology and boundary effects
• Each flag has a severity and a concrete fix, not just an observation
• Assumptions made from a thin brief are labelled as assumptions

Anti-Patterns

• Do not net offsets or removals against gross emissions in the headline number — report gross, then offsets separately
• Do not present a market-based scope 2 figure without naming the contractual instruments behind it
• Do not let a YoY "reduction" stand if it is driven by a factor-vintage update or boundary change — say so
• Do not treat spend-based proxy data as if it supports precise claims — flag it as directional
• Do not silently drop scope 3 categories — every exclusion needs a reason and a size estimate
• Do not certify compliance — this is a rigor review; assurance and legal sign-off stay with the professionals

Based On

GHG Protocol Corporate Standard and Scope 2/Scope 3 guidance practice (boundaries, dual reporting, data-quality tiers, recalculation policy).