Words by TONY WHITEHEAD
The embodied carbon of materials is a hard concept to sell — and an even harder one to define and measure. But one thing is certain: this unseen footprint needs to fall
Like most visitors to the Empire State Building, I found the view from the top quite astonishing: a towering sea of concrete, brick, steel and glass — billions upon billions of tonnes of it — stretching for mile after dizzying mile into the smog-hazed horizons of New York City. But just as memorable was the awestruck comment of the man leaning on the rail next to me: “Dear Lord,” he said, ”just look at all this … all this stuff!”
All this stuff is what embodied carbon is about. When materials are manufactured, energy is almost always consumed, often in large amounts. The World Steel Association estimates that the manufacture of steel is responsible for 7-9% of global carbon dioxide (CO2) emissions from fossil fuels; a 2018 report from the Chatham House think tank put the contribution from concrete — also energy-intensive in its manufacture — at around 8%. Over the lifespan of a typical office building, analysis by Sturgis Carbon Profiling finds that embodied carbon might represent 35% of the total carbon “bill”. For a warehouse, the proportion rises to 47%; for a residential block, to 51%.
So there has been a dawning realization in recent years that it is not enough to reduce what has become known as “operational carbon” — that is, the carbon emitted by burning fossil fuels to heat, light, cool and power a building. If we are ever to get anywhere near a zero-carbon future, then embodied carbon too has to fall dramatically.
A tricky concept
There are reasons why embodied carbon tends to be relegated in importance behind operational carbon — not least that it is a harder sell. If designers can reduce energy costs, then that is an easily understood win-win. The client saves on fuel bills and the planet suffers less. In contrast, a building owner or a developer might question why it’s in their interest to take on any cost associated with material choices that reduce embodied carbon.
But altruism is far from the only reason to opt for low embodied carbon design, according to Fiona McGarvey, senior sustainability consultant at WSP in London. Many building clients now have corporate-level targets on reaching net-zero carbon, she points out: “It’s not possible to do that without considering embodied carbon. For many companies the only realistic way to achieve it will be by purchasing offsets — so they may find it’s actually cheaper to pay more to reduce embodied carbon than to do business as normal and pay for the offsets.” Then there is the potential reputational damage of not addressing your carbon footprint: “Effectively another cost to set against the effort to design with carbon in mind.”
“Sure, everything to do with embodied carbon is inaccurate to a degree. But the value lies in comparative analysis — compare apples with apples and it’s okay if the figures are not perfect”Katie Symons, New Zealand government