Why Cars are Like Buildings and Why Embodied Carbon Matters

As operating emissions become less important, embodied emissions become more so.

Wooden Race car
Ron Harris's wooden F1 Car 1967.

Lloyd Alter at the V&A Plywood Exhibition

A report from clean transport campaign group Transport and the Environment, titled "How Clean Are Electric Cars," demonstrates that electric vehicles are a massive improvement over Internal combustion engine (ICE) powered cars, noting the good news:

"...The latest evidence shows that an average EU electric car is already ​ close to three times better than an equivalent conventional car ​today. Crucially, electric cars will get considerably cleaner in the next few years as the EU economy decarbonizes, with average EVs [electric vehicles] more than four times cleaner than conventional equivalents in 2030."
Lifetime emissions
Blue line is the cleanest battery production, using the cleanest electricity. Transport and Environment

The report included a graph showing how quickly electric cars "repay their carbon debt" compared to ICE cars, the debt being roughly 15% greater upfront carbon emissions, or embodied carbon, which is mostly due to the manufacture of the batteries. And as batteries continue to improve, that extra carbon debt will get smaller. It's very clear, looking at the graph, that compared to an ICE car and taking into account the total carbon picture, the embodied energy is swamped by the operating energy of the ICE-powered cars. From a lifetime carbon point of view, It's pretty obvious how much better electric cars are than ICE cars.

But something about this graph looked very familiar.

operating vs embodied
Building Science

Twenty years ago, graphs describing energy use in buildings looked exactly like the one Transport and the Environment showed for cars. The preoccupation was the reduction of operating energy, and not many in the architecture and engineering biz were too concerned about embodied carbon. Engineer John Straube wrote in the Building Science blog that "Scientific life-cycle energy analyses have repeatedly found that the energy used in the operation and maintenance of buildings dwarf the so-called 'embodied' energy of the materials."

changing relationship
credit: John Ochsendorf/MIT

But a funny thing happened over the 20 years, as buildings got more energy efficient: the embodied carbon became a more significant component of the total carbon, and in fact, soon overwhelmed it in importance. In some highly efficient buildings now, the embodied carbon can be as much as 95% of the lifecycle carbon.

Dalston Lanes under construction
I don't see much embodied carbon here. credit: Waugh Thistleton Architects/ Photo Daniel Shearing

This is the reason why there is a construction revolution going on, and the big switch to mass timber; because making steel and concrete produces about 15% of the world's carbon emissions, and they are the upfront emissions, the embodied carbon in buildings. Because when you reduce or eliminate operating carbon by getting efficient or going all-electric and renewable, embodied emissions dominate.

So What Does This Have To Do With Electric Cars?

Nissan Leaf
Cumulative greenhouse gas emissions for an average new conventional car versus a new Nissan Leaf. Carbon Brief

Here's that graph again, this time comparing a Nissan Leaf to a conventional car. It's being used by Carbon Brief to demonstrate how much better electric cars are than ICE cars over their lifetime; the total lifetime emissions are a fraction of what the ICE car has. But now, the embodied emissions dominate.

Lifecycle greenhouse gas emissions for conventional and electric vehicles (by country) in grammes CO2-equivalent per kilometre,
Lifecycle greenhouse gas emissions for conventional and electric vehicles in grammes CO2-equivalent per kilometre,. Carbon Brief

Now look what happens when you measure the lifecycle carbon emissions in grams per kilometer traveled, based on 150,000 kilometers of lifetime driving. Operating emissions for the Tesla on the right, a U.S.-built car using a U.S. energy mix (the fuel cycle) are less than half of the ICE car. As the grid and battery production gets cleaner it will continue to improve. But according to this graph at this time, driving the Tesla Model 3 has emissions of 147 grams per kilometer, or 236 grams per mile, Building the car and the battery totals 68 grams per kilometer or 109 grams per mile, That's solid embodied carbon.

This is where the rubber meets the road, because the average American drives 13,500 miles per year, which at 236 grams per mile is responsible for 3,186 kilograms or 3.186 tonnes of CO2 per year. That's bigger than the 2.5 tonnes average total emissions per person that we have to stay below by 2030 to hold the global temperature rise to 1.5 degrees Celsius, and just slightly under the 3.2 tonnes average personal budget to stay under 2 degrees Celsius.

Hummer EV
A dominating front end.  GMC

Now imagine the numbers if we start figuring it out for electric SUVs and pickup trucks, which could have embodied carbon of 40 to 60 tonnes of CO2, consume more electricity and have much bigger batteries. Those grams per mile could be triple.

We have discussed this before in Electric Cars are Not a Silver Bullet, which covered similar ground, noting then that vehicle size and weight mattered, and where the researchers concluded that "the arsenal should include a wide range of policies combined with a willingness to drive less with lighter, more efficient vehicles." Heather Maclean noted in a press release:

"EVs really do reduce emissions, but they don't get us out of having to do the things we already know we need to do. We need to rethink our behaviours, the design of our cities, and even aspects of our culture. Everybody has to take responsibility for this."

What Can We Learn From the Building Industry?

Development stages
World Green Building Council

The leaders in the industry quickly realized that just reducing embodied carbon wasn't enough, that we have to change the way we think about building. The World Green Building Council starts with building nothing and exploring alternatives, which might be bikes. The next steps are to build less; what do we really need? Maybe a cargo bike would be enough. to build clever, optimizing material use, and to build efficiently. All of these apply to mobility; it makes no sense to drive an F-150 EV to the grocery store.

The lesson from the building industry is that when you get rid of operating carbon, then embodied carbon dominates, and you have to do everything you can to reduce it. You definitely can't just say that a wood building or electric car is emissions-free, because embodied carbon dominates.

The same rules apply for transportation as in architecture; In the mobility world, that means smaller, lighter vehicles, perhaps going from four wheels to three and to two and to none wherever and whenever possible.

DKW Wooden car
1937 DKW car with wooden frame (red in cutaway) and body. Lloyd Alter @ V&A Plywood show

Or maybe we should just build cars out of wood again, like DKW (later Audi) did in 1937.

View Article Sources
  1. "How Clean Are Electric Cars?Transport & Environment.

  2. Straube, John. "BSD-001: Why Energy Matters." Building Science Corporation, 2010.