Meme Weeding: Embodied Carbon
The greenhouse gases emitted by the production of concrete, called embodied carbon, are occasionally used as a green-NIMBY argument against building new things. A Berlin Green spokesperson coauthored a study opposing U-Bahn construction on the grounds that the concrete used in construction would raise emissions. More recently, I’ve seen American opponents of transit-oriented development in Manhattan, of all places, talk about the high embodied carbon of new high-rise buildings. Katja Diehl calls for a moratorium on new buildings on anti-concrete grounds, and a petition for the EU to shift regulations to be against new buildings and in favor of reuse on embodied carbon grounds got written up favorably by Kate Wagner in the Nation. Against all of this, I’ve found some numbers on the actual emissions involved in concrete production for new buildings, and they are so low as to be insignificant, 1.5 orders of magnitude less than transportation emissions. A decarbonization strategy should largely ignore embodied carbon concerns and embrace pro-growth sentiments: big buildings, big subway systems, big cities.
What is embodied carbon?
Embodied (sometimes called embedded) carbon is the carbon content emitted by the production of materials. The production of concrete emits greenhouses gases, mainly through two mechanisms: the chemical process used to produce cement emits CO2 by itself, and the energy used for production adds to the emissions of the electric grid.
What are the embodied carbon emissions of new buildings?
The embodied carbon content of concrete depends heavily on the local electricity grid as well as on the required strength of the material, with stronger requirements leading to higher emissions. The Climate Group commissioned a report on this in the British context, finding a wide range, but the average is around 250 kg of CO2-equivalent per m^3 of concrete, the 75th percentile is about 300, and the upper bound is 450. This is a cradle-to-gate figure, taking into account the existing conditions of the carbon intensivity of where concrete is produced and of the logistics system for getting it to the construction site. This is already with some reductions from a previous baseline (EC100; the UK average is around EC60), and further reductions are possible, through decarbonizing the logistics and production; the goal of the report is not to bury the concept of embodied carbon as I do but to propose ways to reduce construction industry emissions.
The question is now how to convert cubic meters of concrete into square meters of built-up area. I have not seen European figures for this, but I did find a 2012 report by the Building and Construction Authority. In Singapore, the sustainability index used is the concrete usage index (CUI), measured in meters (cubic meters per square meter). The example projects given in the study, all around 15 years old, have a CUI of 0.4-0.5 m, and it was pointed out to me on social media that in Toronto the average is 0.55 m.
250 kg/m^3 times 0.4 m equals 0.1 t-CO2 per m^2 of built-up area. A 100 m^2 apartment thus has an embodied carbon content of around 10 t-CO2. This is relative to a baseline in which there is already some concern for reducing construction emissions, both the CUI and the carbon content of concrete per m^3, but this is largely without techniques like mass timber or infra-lightweight concrete (ILC). In Singapore the techniques highlighted in the BCA report are fully compatible with the city’s high-rise character, and the example building with gold but not platinum certification has 25 stories.
Should we worry about construction emissions?
No.
An aggressively YIMBY construction schedule, say with 10 dwellings built annually per 1,000 people, say averaging 100 m^2, emits around 0.1 t/capita annually: 0.1 t/m^2 * 100 m^2/unit * 0.01 unit/capita. All figures have ranges (and if anything, 100 is high for the places that build this much urban infill housing), but factor-of-1.5 ranges don’t erase an order of magnitude analysis. The emissions produced by construction, even if it were raised to some of the highest per capita rates found in the developed world – in fact higher rates than any national average I know of – would be about two orders of magnitude lower than present-day first-world emissions. They’d be 1.5 orders of magnitude lower than transportation emissions; in Germany, transport is 22% of national emissions and rising, as all other sources are in decline whereas transport is flat.
There’s a lot of confusion about this because some studies talk about buildings in general providing a high share of emissions. The Bloomberg-era PlaNYC spoke of buildings as the top source of emissions in New York, and likewise the Nation cites WeForum saying buildings are 37% of global emissions, citing a UN report that includes buildings’ operating emissions (its topline figure is 10 Gt in operating emissions, which is 27% of global emissions in 2022). But the construction emissions are insignificantly low. This means that aggressive replacement of older buildings by newer, more energy-efficient ones is an unmixed blessing, exactly the opposite of the conclusion of the green movement.
Instead of worrying about a source of emissions measured per capita in the tens of kilograms per year rather than in the tons, environmental advocates need to prioritize the most important source of greenhouse gases. The largest in developed countries is transportation, with electricity production usually coming second, always falling over the years while transport remains flat. In cold countries, heating is a significant source of emissions as well, to be reduced through building large, energy-efficient apartment buildings and through heat pump installation.
Regulations on new construction’s embodied carbon are likely a net negative for the environment. The most significant social policy concerning housing as far as environmental impact is concerned is to encourage people to live in urban apartment buildings near train stations. Any regulation that makes this harder – for example, making demolitions of small buildings to make room for big ones harder, or demanding that new buildings meet embodied carbon standards – makes this goal harder. This can be understandable occasionally if the goal of the regulation is not environmental, for example labor regulations for construction workers. It is not understandable if the goal is environmental, as the concern over embodied carbon is. People are entitled to their opinion that small is beautiful as a matter of aesthetic judgment, but they are not entitled to alternative facts that small is environmentally friendly.










