The publication of an empirical measure of a given product’s embedded carbon makes sense for both the manufacturer wishing to espouse his virtuous practices to potential clients, and for the client seeking hard environmental data on which to base his choice of supplier.
But, just like statistics, carbon footprinting data can be skewed − whether intentionally or not − to make a product or service appear more environmentally friendly than it really is.
It would not be difficult to make something look sustainable by quoting the low number of tonnes of carbon dioxide (CO2) emitted in its manufacture, while neglecting to mention the many tonnes of other greenhouse gases that are emitted.
These other gases are conventionally expressed in terms of what concentration of CO2 would cause equivalent environmental detriment (a unit denominated as CO2e).
Despite being huge in significance, the absence of that little “e” on marketing material is unlikely to be noticed by an uninformed eye.
Even when all the relevant emissions are included in the calculation, there is no standard as to what parameters are used. If you are calculating the embedded carbon of a product, do you calculate every step of the journey up to the end of manufacture?
Or do you continue after that, including distribution, and delivery to site, and installation of the product on site? How about operational emissions during the life of the product? And end-of-life disposal?
With manufacturers free to set parameters wherever they like, the chance of being able to make a meaningful like-with-like comparison becomes slim.
But even if the parameters are known to be equal, reliable data is not always available to perform the calculation.
The University of Bath’s Inventory of Carbon and Energy is one of the most prominent tools detailing the embedded carbon of building materials, but it - like other, similar data sets - bases its values for some materials on only generic secondary data.
Precast concrete is one of those materials, and it was this lack of good data that prompted the Concrete Pipeline Systems Association (CPSA) to launch a project to improve upon the data available to the industry.
In June, the association published a series of reports based on an audit in which primary data was collected from its member organisations.
The project has created what the CPSA says is a much more accurate picture of embedded carbon in precast concrete products, based on British Standard PAS2050 for the methodology of calculating greenhouse gas emissions.
The project showed that the minimum value that could be calculated for precast concrete from the University of Bath data − 184g of CO2/kg − was inaccurate. CPSA found that the figure for such products was more likely to be in the range of 140g CO2/kg to 160g CO2/kg.
“Their figures are … overstating the embodied carbon,” says CPSA business development director Stuart Crisp.
Equally, he is concerned that other materials’ embedded carbon may be understated in the University of Bath data. “That’s one of our biggest concerns, that there’s an error creeping in here,” he says.
The CPSA carbon footprinting reports are a valuable asset for those companies manufacturing and using precast concrete products and could lead to much greater comparability between different companies’ processes and methods.
But they fall short in terms of comparability with alternative materials such as plastics, simply because an equivalent robust study based on primary data has not yet been done for plastics.
The CPSA data can only be meaningful and useful in applications where it can be compared with other data collected under the same methodology.
The industry as a whole would benefit if other manufacturing sectors conduct their own equivalent studies.
Carbon footprinting is still a young and often manhandled science, but the lack of a unified approach across the construction industry means the potency of good work such as the CPSA’s is limited.
The incoming European standard EN15804 for environmental product declarations (EPD) in construction could help to bring about a more consistent, comparable industry approach to calculating embedded carbon.
That unified approach could be the first step towards reaching the problematic dream of having transparent, comparable carbon footprints right across the industry.