Civil engineers play a vital role in minimising climate impacts by understanding and reducing the whole-life carbon of infrastructure. 

Some 70% of carbon emissions worldwide can be linked to infrastructure, of which the built environment contributes about 38%. Infrastructure is responsible for more than half of the UK’s total carbon emissions.  

Measuring and monitoring carbon is therefore critical to meeting both the sector’s climate commitments and those of the country and the world at large.  

Measuring carbon at all stages of a project lifecycle is integral to reducing carbon emissions – without measurement, we cannot know if interventions are delivering the desired change.  

Measurement is also a requirement for many UK and EU projects. In 2016, the BSI (British Standards Institution) facilitated the development of PAS 2080, the world’s first international specification for cutting carbon emissions arising from construction. The specification was updated and accompanied by an ICE-curated Guidance Document in April 2023.

The term ‘carbon’ is used as shorthand for the carbon dioxide equivalent of all greenhouse gases. The metric ‘carbon dioxide equivalent’, abbreviated as CO₂e, is used to compare emissions and materials on the basis of global warming potential (GWP).  

For example, according to Eurostat, the GWP for methane is 25 and for nitrous oxide it is 298. This means that the emissions of 1 tonne of methane and nitrous oxide respectively is equivalent to 25 and 298 tonnes of carbon dioxide.   

The Environment Agency’s carbon calculator measures the CO₂e of construction activities by calculating the embodied CO₂e of a material plus the CO₂e associated with their transportation, providing a CO₂e tonnage (tCO₂e). When measuring carbon in kilograms, engineers refer to ‘kgCO₂e’.  

 The Construction Leadership Council recommends that an engineering carbon assessment be presented as follows:  

• Total kgCO₂e – i.e. the total capital carbon footprint  
• Total kgCO₂e per material or major scope, appropriate to the asset – i.e. kgCO₂e per linear km of rail track, or CO₂e per m² of concrete 
• Total tCO₂e per £100,000 cost

Carbon reporting then typically looks at three ‘lifecycle’ stages: 

Engineers may only be required to report and measure on 01 (embodied carbon) or 02 (operational carbon) above, according to the stage of the project for which their firm is responsible. 

However, a whole-life carbon measurement approach is considered best practice as this provides the best opportunity for reducing lifetime emissions while also helping to avoid any unintended consequences that may come from focusing on operational emissions alone. 

For example, triple-glazed windows may be bulkier and have more embodied carbon, but their performance over a building’s lifetime will greatly reduce whole-life carbon.

The recently updated PAS 2080:2023 specification emphasises the importance of using a carbon reduction hierarchy to help identify opportunities for tackling whole-life carbon in the decision-making process. This hierarchy applies not just to new-builds but to wider built environment projects and programmes.

The intention is that the hierarchy should be applied to all emissions as the specification groups them: capital, operational and user emissions. The greatest influence over whole-life carbon reduction is at the earlier 'need' stage, during which objectives and outcomes of projects and programmes are still being developed and assessed.

Accurate carbon measurement requires data of sufficiently high quality. Having complete data sets of sufficient granularity and transferability allows for lessons to be learnt across projects or assets and between phases.  

Sarah Jolliffe, carbon reduction lead at BAM UK and Ireland, recommends environmental product declarations (EPDs) and supply-chain datasets as rich sources of information. “There are a lot of spreadsheets, but it's very robust information with a lot of technical granularity, which is great to use,” she explains.  

Jolliffe recommends working with, or directly hiring, data analysts. “There’s no shortage of talent out there,” she says. 

The approach to carbon measurement depends on the project lifecycle, covering embodied, operational and whole-life carbon. There is also an increasing awareness of the need to influence carbon reduction in existing infrastructure, as well as in new-builds.  

Ideally, decarbonisation starts at the earliest feasibility stage, explains James Fiske, chief executive of BCIS (Building Cost Information Service, part of the Royal Institution of Chartered Surveyors – RICS). “For example, if you’re building a warehouse, what's the carbon associated with building it? Is it steel-framed or concrete-framed? You calculate carbon per metre squared to give an indicative carbon cost range.”  

Once the project is under way, “then there will be an evolving design process and decisions made on concrete, steel, types of cladding, roof – getting progressively more detailed until you get to the point where you're specifying the performance of a material itself”, he says. (See diagram.)

 This diagram also introduces the ‘cradle to…’ terminology. The two most-used terms are ‘cradle to gate’, covering the carbon associated with bringing raw materials to the ‘gate’ of the construction site, and ‘cradle to grave’, which covers the entire building or infrastructure lifecycle.  

Dr Kat Ibbotson, director of strategic advisory at WSP and a steering group member for PAS 2080, explains: “Currently, where the carbon impact of an infrastructure project is assessed at all, the boundary scenario used is often ‘cradle to gate’… Such assessments consider materials, manufacture, transport and, sometimes, construction process, but take no account of the carbon impact of the user behaviour that the asset will support, the carbon cost of operating the asset, or how the asset will be disposed of or re-used.”  

The 2022 ICE report Meaningful Measurement for Whole-life Carbon in Infrastructure recommends that methodology for carbon calculation conforms to PAS 2080, uses RICS methodology to calculate embodied carbon, and is aligned to ISO 14025. The report, authored by Ibbotson, states that the project lifecycle should cover:  

Where the first assessment takes place before product selection, initial calculations should be based on (in order of priority): publicly available company-specific benchmarks; industry benchmarks or estimated quantities; and use of the Inventory of Carbon and Energy database.

There remain inconsistencies in the carbon reporting methods used in the industry as well as a lack of available skills. “At the moment, if you ask three or four carbon assessors to assess the same building, they will come up with different answers,” Fiske explains. This makes it difficult to compare, improve and learn from other construction projects.   

A 2022 UK House of Commons Committee report into net zero concluded that there were “issues associated with the lack of consistent data sources and measurement metrics” and “significant skills gaps… in the measurement of embodied and whole-life carbon and the use of low-carbon materials”.  

The sector needs to significantly improve its use of data for consistent and transparent whole-life carbon reporting. Among the necessary remedial actions mentioned in the ICE’s Meaningful Measurement report are “behavioural change (considering data earlier and handing it over appropriately throughout the lifecycle), considering design and construction alterations from a whole-life carbon impact perspective… and clear and consistent reporting”. 

Clear and consistent reporting starts with benchmarking – the process of measuring key metrics and practices, and comparing them against previous projects. Effective whole-life carbon measurement for infrastructure can therefore be improved via benchmarking as a point of reference.   

The Infrastructure and Projects Authority (IPA) recommends a top-down approach to benchmarking, initially establishing a range of performance metrics to reflect the project objectives. 

This approach breaks a project down into components or asset groups, comparable across a range of other projects. For example, a tunnel from a railway project can be compared with a tunnel from a road or utility project. Benchmarks for each component are then sourced.   

Another approach is to “benchmark the material”, Jolliffe suggests. For example, “There are upwards of 300-400 different concrete mix designs, so you can benchmark those – it can be more valuable to focus on the product,” she says. (See example below.) 

Given the ‘risks and challenges’ outlined in the previous section, benchmarking is crucial to achieving consistency across the industry. In response, a consortium of professional bodies across the industry, including the ICE, has set up the Built Environment Carbon Database (BECD), recognising “that a lack of available and consistent data is one of the main barriers that remains unresolved”. 

As of April 2023, the BECD intends to plug this gap with the high-level data required to estimate different options and appraise the feasibility of projects. The success of PAS 2080 has always relied on the availability of high-quality data; now, the BECD aims to finally provide it.  

Crucially, the BECD will be industry-led via a single data repository, meaning it requires the ongoing input of on-the-ground engineers. Data-sharing across industry, not just internally, becomes vital. This includes benchmarks for operational carbon, and more detailed product-level information to appraise embodied carbon options. (See diagram below.) 

Ibbotson adds: “Achieving consistency and quality of data is a huge step in the right direction.” Access to industry-wide benchmarking data via the BECD will improve value across the supply chain and allow for more accurate whole-life carbon reporting. 

Data-sharing challenges, such as commercial sensitivities, can also be mitigated and reduced by clear terms of reference or non-disclosure agreements (NDAs). 

Consistent methodology and consistent data are required to produce accurate carbon measurement. Carbon assessment in the sector is evolving into a clearer, more precise environment.   

Ultimately, however, when using any tool for carbon measurement, Jolliffe recommends keeping the end goal in mind: the aim is not simply to ‘reduce’ carbon. The critical measurement is how close it brings the project (and the organisation and nation) to net-zero emissions.   

As Ibbotson puts it: “Engineers are problem-solvers – and we have both the skill and, I believe, a responsibility to use those skills to help the world meet the climate emergency.”