How to Understand the Scale of Embodied Carbon

Engineer Will Arnold has come up with a clever way of demonstrating the scale of upfront carbon emissions, a problem many have been wrestling with.

Whenever we talk about fixing old buildings instead of tearing them down and replacing them, you can see eyes glazing over. They say the new building will be sustainable and energy efficient! Or, where I live in Toronto, they will tear down a 20-story rental apartment building to build a 50-story condo building and say, "We need more housing!"

When we bring up the embodied or upfront carbon produced to replace the building, those eyes start rolling.

The architects and engineers working on new building projects always have an argument and usually a study to accompany the claims.

For American firm Diller Scofidio + Renfro and its British associates Sheppard Robson, a life-cycle assessment accompanied the proposal to take down and replace the Bastion House in London. The assessment concluded that "retaining existing building fabric does not achieve the most sustainable outcome for this transformative and strategic site," even while it admitted that "the preferred redevelopment option will require more carbon spend in absolute terms." It also found that the new building will produce 15 additional million kilograms of CO2, or 15,000 metric tons. "This is approximately a 50% uplift in embodied carbon," said the report.

But how much is that? How can people get a sense of it?

One of the problems is that people cannot visualize the scale of the carbon emissions involved. Many have tried to make it visible. We recently showed how electric motorcycle company Cake built a cube enclosing the 1,186 kilograms of CO2 of upfront emissions from making a bike. I thought weight was better than volume.

For an upcoming book, I was thinking of T. S. Elliot's "The Love Song of J. Alfred Prufrock," who said, "I have measured out my life with coffee spoons." But they are only 26 grams of stainless steel—roughly 50 grams of upfront carbon—so that's a bit small. Instead, I have been measuring CO2 in terms of Wile E. Coyote's ACME anvils at 100 kg/anvil so that Cake's bike would be a pile of 12 anvils. I might use the 50-gram unit I call the Prufrock for smaller items.

Arnold has a better idea. He is currently the head of climate action at the Institution of Structural Engineers, where he famously wrote we should use less stuff. But previously worked at engineering giant ARUP, where he wrote an article "Reducing Carbon Emissions ... Every Working Day."

The creative leap Arnold took was to frame the carbon in buildings in terms of those carbon footprint items we have been told about for years—your flight to Europe is a ton of carbon! A year's worth of meat is 2 tons! Driving your car is 3 tons per year! Actually, the EPA said the American average is 4.6 metric tons, and total emissions from the average American are about 15 metric tons. A hamburger is 2.5 kilograms.

These are numbers that anyone who reads Treehugger has been bombarded with for years. When Arnold puts embodied carbon in terms of people or things, it is easier to visualize.

"What can you do about it? Well, as an example, if you agree to columns that are closer together, limit the number of storeys, and allow the engineer to spend more time optimising the structure, you might halve it. That’s a saving of 3000 tonnes of embodied carbon… twenty lifetimes of veganism! Bigger still are the savings you can make through re-use. Remember that embodied carbon is the carbon associated with making something. If you can manage to avoid constructing a new structure altogether, you just saved 6,500 tonnes of carbon! And even on a small building (say a block of ten apartments), if you can reuse the foundations of whatever used to be on the same site, you could save in the order of 100 tons of carbon. That’s the yearly emissions of you plus nine friends of your choosing."

So, if we take a recent example covered in Treehugger, William McDonough's Apex Building, switching from concrete to cross-laminated timber reduced upfront carbon emissions by the equivalent of 53 people-years or 323,000 hamburgers. Had they not been forced to build that massive parking garage, it could have saved the equivalent of 3,234 cars driving for a year.

Or the replacement of Bastion House with its 15,000 metric tons of additional upfront emissions: that's a thousand people-years. It's 5,000 British car years.

Arnold is speaking to building professionals here, pointing out that they are responsible for vast carbon emissions in their choices and decisions, and biking to the office won't cut it.

"So remember: as built environment professionals, your greatest contribution is professional, not personal. I’m not saying that we shouldn’t also consider skipping flights or reducing our meat consumption. But we are in a unique position to make changes with hundreds of times more impact than that. And it is by finding ways to re-use more of our existing assets and embed carbon efficiency in our project briefs, that we will make the most substantial contribution to a sustainable future on Earth."

Arnold is right. Individual actions matter, but the individual and collective actions building professionals take at work matter a lot more.