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Articles on GHG verification, clean fuel and aviation compliance

Technical writing from the KeeWee verification team: how the rules work, what verifiers find, and the methods behind the numbers.How the rules work, what verifiers find, and the methods behind the numbers.

FeaturedVerification practice

Comprehensive Guide to Assurance and Verification Conclusions: Unmodified, Emphasis of Matter, Modified, Adverse, and Disclaimer

A practical reference for GHG verifiers and sustainability assurance practitioners. It explains the five types of assurance conclusion: unmodified, emphasis of matter, qualified, adverse and disclaimer. For each type it covers when it applies, standard wording for both reasonable and limited assurance, and the clause references in ISSA 5000, ISO 14064-3, ISO 14065 and ISO/IEC 17029. It also includes a decision matrix and a decision tree based on materiality and pervasiveness.

Minxing Si7 min read
FeaturedVerification practice

Comprehensive Guide to Assurance and Verification Conclusions: Unmodified, Emphasis of Matter, Modified, Adverse, and Disclaimer

A practical reference for GHG verifiers and sustainability assurance practitioners. It explains the five types of assurance conclusion: unmodified, emphasis of matter, qualified, adverse and disclaimer. For each type it covers when it applies, standard wording for both reasonable and limited assurance, and the clause references in ISSA 5000, ISO 14064-3, ISO 14065 and ISO/IEC 17029. It also includes a decision matrix and a decision tree based on materiality and pervasiveness.

Minxing Si · 12 Oct 2026 · 7 min read

Quick answers

What is a PEMS?

A predictive emissions monitoring system estimates stack emissions from process data a facility already records, with no analyzer on the stack. It is an accepted alternative monitoring method in Canada and the US.

Build one with an AI assistant

What is CORSIA?

The Carbon Offsetting and Reduction Scheme for International Aviation, run by ICAO. Airline operators monitor and report their CO₂ emissions and offset growth with CORSIA Eligible Emissions Units.

Read the CORSIA series

What are the Clean Fuel Regulations?

Canada’s federal rules, administered by ECCC, that require suppliers of gasoline and diesel to lower the carbon intensity of the fuel they supply, with credits that must be verified.

What verifiers found in 2022 and 2024

What is a PEMS?

A predictive emissions monitoring system estimates stack emissions from process data a facility already records, with no analyzer on the stack.

Latest articles

Older articles
Reading path · 4 articles · about 16 min

CORSIA for airline operators, in order

From the simplified monitoring route for small emitters to offsetting and sustainable aviation fuel.

All CORSIA articles
  1. Part 1 · 4 minDemystifying CORSIA: A Guide to Simplified CO₂ Monitoring for Small Airline Operators
  2. Part 2 · 3 minPrecision Reporting: Mastering CORSIA Fuel Monitoring Methods for Large Airline Operators
  3. Part 3 · 3 minUsing Offsets Under CORSIA: CORSIA Eligible Emissions Units (EEUs)
  4. Part 4 · 6 minCORSIA – Sustainable Aviation Fuel
Reading path · 4 articles

CORSIA for airline operators, in order

Start with part 1

All articles

17 articles · newest first

Turn reading into a credential

Course 101 teaches ISO 14064-3 verification end to end. Pass the final assessment to earn a Certificate of Attainment from KeeWee.

See Course 101 · $350 USDWatch a free lesson