The GHG Protocol (Greenhouse Gas Protocol), developed by the World Resources Institute and the World Business Council for Sustainable Development, is the reference standard for greenhouse gas emissions accounting. First published in 2001, regularly updated, it structures three major accounting perimeters (the scopes) and has established itself as the reference for lenders, regulators and derived standards (TCFD, ISO 14064, national standards).

For an infrastructure project under DFI financing, mastery of the GHG Protocol has become an almost mandatory competence. The Equator Principles in their version 4, the 2023 AfDB ISS revision, the World Bank's Environmental and Social Framework on certain aspects, require quantification aligned with the Protocol for high-emission projects.

This article presents the calculation methodology for the three scopes applied to an infrastructure project, the specific difficulties for construction regarding activity data, the central question of temporality (construction versus operational emissions), and the most frequent methodological pitfalls.

Scope 1: direct emissions from the project

Scope 1 covers emissions produced by sources owned or controlled by the project itself. For an infrastructure project, four categories dominate.

Emissions from equipment and vehicles. Combustion of diesel, petrol or natural gas in excavators, lorries, bulldozers, cranes, concrete mixers, compressors. The methodology consists of collecting actual fuel consumption (litres or kilogrammes) and applying the corresponding emission factors (kg CO2 per litre, according to fuel type and reference country).

Emissions from fixed installations on site. Emergency generators, electric or thermal concrete plants, heating or air-conditioning installations for base camps.

Industrial process emissions, for projects that involve them. Own cement works, ore processing, water or wastewater treatment with biogenic methane emissions.

Fugitive emissions. Refrigerant gases from air-conditioning equipment, sulphur hexafluoride from high-voltage electrical equipment, methane from reservoirs, gases during purging and testing.

For a standard construction site, scope 1 often represents 10 to 25% of the total footprint. The share increases for projects that operate their own power plants.

Scope 2 covers indirect emissions related to energy consumed but produced outside the project's perimeter. Electricity purchased from the grid is the main item; heat or steam purchased from an external supplier also fall under scope 2.

The methodology is simpler to state than to apply. Consumption is measured in kWh or MWh. The emission factor is the average carbon content of the supplier's electricity mix or, failing that, of the national grid. These factors are published by international agencies (IEA, IFIs) and updated periodically.

Two approaches coexist for calculation. The location-based method uses the average mix of the local grid, applicable regardless of supplier. The market-based method uses the specific mix of the contractual supplier, which may be more virtuous (certified green electricity) or more carbon-intensive than the average. The GHG Protocol, since its Scope 2 Guidance of 2015, recommends reporting both methods in parallel.

For an infrastructure project in the construction phase, scope 2 is often modest, in the order of 5 to 15%. It becomes significant for projects that consume large amounts of electricity (tunnel-boring machines, electric concrete plants, treatment installations).

Scope 3: value chain emissions

Scope 3 covers indirect emissions that are neither in scope 1 (direct sources) nor in scope 2 (purchased energy). The GHG Protocol's Scope 3 Standard distinguishes fifteen categories, of which seven are particularly relevant for an infrastructure project.

First category, purchased goods and services. This is often the dominant category for a construction project: cement production, steel manufacturing, extraction and processing of aggregates, production of surfacing materials, cables, mechanical equipment. Quantification relies on physical quantities consumed multiplied by material emission factors (kg CO2 per kg of cement, per kg of steel).

Emission factors for construction materials are well documented by professional associations and public databases (ICE database from the University of Bath, Base Carbone ADEME in France, EcoInvent). For specific materials or for suppliers that publish their own Environmental Product Declarations (EPD), specific factors are more precise.

Second category, upstream transport. Transport of materials and equipment from production sites to the construction site. Quantification combines tonne.km travelled by tonnes of materials and emission factors for the mode of transport (maritime, road, rail).

Third category, business travel. Journeys by project teams, consultants, supervision missions. Generally a minor item but not negligible for international projects involving multiple nationalities.

Fourth category, employee commuting. Quantified via surveys or sector ratios.

Fifth category, capital goods. For a project that invests in durable equipment (machines, vehicles specific to the project), quantification combines the tonnes of steel, copper, plastic mobilised and the corresponding emission factors.

Sixth category, end-of-life treatment. Future demolition, construction waste treatment, landfill or recycling scenarios. This category is particularly significant for long-life infrastructure.

Seventh category, use of sold product. For a motorway, the emissions from the traffic it supports over its lifetime. For a building, the emissions related to its energy consumption over 30 to 50 years. This category, sometimes debated methodologically, is both the heaviest and the most difficult to quantify precisely.

For a standard infrastructure project, scope 3 frequently represents 70 to 90% of the total footprint. Ignoring this scope amounts to radically minimising the real footprint.

Temporality: construction versus operation

A structuring dimension, often poorly handled, is the temporality of emissions. An infrastructure project produces massive emissions during its construction (a few years), then generates residual emissions or induced traffic throughout its operational phase (several decades).

The GHG Protocol recommends presenting the two periods separately, with a cumulative calculation over the lifetime for comparability. This presentation avoids confusion between a project with high construction emissions but low operational emissions (a railway infrastructure for example) and a project with constant and high emissions.

The discounting of future emissions is a methodological debate. Some approaches discount (a tonne emitted in 2050 weighs less than a tonne emitted in 2026), others do not (carbon remains in the atmosphere regardless of the year of emission). DFI practice generally leans towards the second approach, which is more conservative.

Common methodological pitfalls

Five pitfalls recur in insufficiently mastered carbon accounting.

Under-dimensioned perimeter. Limiting the calculation to scope 1 or to scope 1 plus 2 gives a very partial picture. The main frameworks now require substantial scope 3 for significant projects.

Undocumented emission factors. Using approximate, unsourced, outdated factors invalidates the calculation under review. Documentary traceability is essential.

Double counting. Steel production emissions can be counted in the scope 3 of the purchasing project and in the scope 1 of the steel producer. This double counting is admitted by the GHG Protocol at the global level but must be properly managed at the project level to avoid internal double counting.

Aggregation into a single figure. Presenting an overall footprint without detail by scope and category prevents the reader from understanding where the emissions come from and prevents operational dialogue on possible reductions.

Absence of comparison. A raw carbon footprint figure (a few hundred thousand tonnes of CO2e) means nothing without comparison to similar projects, alternatives, sector benchmarks. This comparison is required by the alternatives analysis required by lenders.

Correctly calculating the carbon footprint of an infrastructure project is not an academic exercise. It is the basis for dialogue with lenders on climate issues, and it is often the exercise that reveals where the most important reduction levers lie.

The method to be applied is demanding but well marked out. Emission factors exist, tools are accessible, practice is gradually spreading in consultancies. The investment required for a project owner wishing to build its capacity in this area is modest compared to the value it produces in terms of climate credibility and financing resilience.

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