GHG Accounting and Emissions Measurement
This domain tests whether you can build a defensible inventory: choose the right boundary, apply the right factors, state the GWP set, and report scope 2 both ways. Most errors are boundary errors or unit errors rather than arithmetic errors.
Core rules and concepts
- Consolidation approach. Equity share, financial control or operational control. The choice changes which emissions appear in scope 1 and must be disclosed.
- Scopes. Scope 1 covers direct combustion, process emissions and fugitive releases. Scope 2 covers purchased electricity, steam, heat and cooling. Scope 3 covers the 15 value-chain categories, upstream and downstream.
- Dual scope 2 reporting. Location-based uses the grid average emission factor; market-based uses contractual instruments such as renewable energy certificates and supplier-specific factors, with a residual mix where instruments are absent. Both are reported; neither replaces the other.
- Calculation. Activity data × emission factor × GWP gives CO2e on a 100-year horizon. AR6 fossil methane is 29.8, non-fossil methane 27.0, N2O 273; AR5 gives 28 and 265; AR4 gives 25 and 298. Always state which set is used.
- Boundary maintenance. Base-year recalculation is triggered by acquisitions, divestments, methodology changes or errors above a stated threshold. Standards: GHG Protocol Corporate and Scope 3, ISO 14064-1, verification under ISO 14064-3.
- Measurement. Continuous emissions monitoring for stacks, flow meters and fuel invoices for combustion, emission-factor estimation for fugitives, and remote sensing or satellite data for methane. Biogenic CO2 from biomass is reported separately outside the scopes.
Worked example
A plant burns 1.2 million litres of diesel at 2.68 kgCO2/L = 3,216 tCO2, and 500,000 m³ of natural gas at 2.0 kgCO2/m³ = 1,000 tCO2. Fugitive methane of 5 t at AR6 GWP 29.8 = 149 tCO2e. Scope 1 = 4,365 tCO2e. It buys 4,000 MWh of electricity; at a location-based factor of 0.45 tCO2/MWh that is 1,800 tCO2, while a market-based calculation using retired certificates gives 0 tCO2, disclosed alongside.
Traps that cost marks
- Double counting one scope 3 category across two companies in the same value chain.
- Using AR4 GWPs when the inventory states AR6.
- Netting certificates against scope 1 emissions.
- Reporting only the market-based scope 2 figure.
- Forgetting that transmission and distribution losses are scope 3 for the consumer.