Embodied emissions

Part 7 of Decarbonising the Built Environment: a Global Overview, by Tom Ackers

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In this part, I give an overview of the problem of embodied emissions, i.e. those emitted in the construction of buildings and infrastructure (section 7.1); then some details about concrete and steel (section 7.2), and cement recarbonation (section 7.3); and about roads (section 7.4). 

7.1. Overview

This graphic shows the sources of the built environment’s embodied CO₂ emissions for 2019, including emissions from steel manufacture.[1] Each row represents a different breakdown of the same total – the 6.6 GtCO2 of embodied, energy-related emissions. The second row, unlike the other two, also shows the process emissions from the production of steel and cement.

Sources: * IEA (2020); △ Robbie M. Andrew (2022); § IEA / UNEP (2020), IEA / UNEP (2021)

The vast majority of the built environment’s embodied emissions come from the burning of fossil fuels during the manufacture of building materials.

For example, in the case of buildings construction, in 2019 just 0.13 Gt CO₂ emissions globally came from the buildings construction stage – a comparatively tiny proportion of the roughly 4.45 Gt total embodied emissions.[2] The rest came from the manufacture of building materials prior to construction.

The Seagram building in New York. Source: Creative Commons

Of the carbon footprint of those materials that went into buildings construction, around 60% of emissions came from cement and steel manufacture, and 40% from the manufacture of other buildings materials. For the construction sector as a whole, the ratio is something like 50:50 cement and steel emissions to other emissions.

This underlines the point, emphasised in part 3: steel and cement (and concrete made from cement) are the high-energy ingredients of choice for fossil-fuelled global construction.

Sand and gravel are also major inputs. Indeed, the construction sector is driving an impending sand crisis. The main emissions cost of these is the energy of extraction, processing and transport.

In addition, construction consumes 26% of global aluminium output and 19% of all non-fibre plastics.

The levels of embodied emissions in common construction materials can be seen in the “Construction Material Pyramid”, shown below, designed by the Centre for Industrialised Architecture in Denmark. The values given are averages that include direct and indirect emissions footprints by point of sale (cradle-to-gate).

At the base of the pyramid are materials that have a low emissions intensity, i.e. that typically require just a small input of energy or other sources of emissions in their production: rammed earth walls, plywood, construction timber. (Wood here even gets a negative value as a material that “sequesters” carbon, although I think that framing can be misleading. See section 8.4 below.)

Contraction and convergence, development and urbanisation

Part 6 of Decarbonising the Built Environment: a Global Overview, by Tom Ackers

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From the perspectives of real human needs and capacities, and present forms of technology, it is perfectly possible for all the world’s peoples and societies to follow a low energy and low emissions economic path from now onwards.

The obstacles to that come from the forces of capitalist growth, and the powerful interests invested in a more destructive future.

The Kibera shanty town in Nairobi, Kenya. Source: Wikimedia / Creative Commons

The obvious rational route to decarbonisation and a more liveable environment is “contraction and convergence”, a concept pioneered by the Global Commons Institute.

It means that the world’s high consumers of materials and energy need to contract their material and energy footprints dramatically; in turn, that creates consumption space for the world’s poor to consume more per capita use-values than they do now – to converge upwards on the per capita living standards of the global north.

All of that needs to happen across all sectors of the economy. It also needs to happen within a shrinking material consumption budget globally – and in the context of steep rises in forecast population.

There is plainly a tension between the extent of “permissible” material consumption, and the enormous needs for social development internationally. At least half the world’s population lives in material poverty.

Quantifying Material Use, Emissions, and the Scale of Decarbonisation

Part 5 of Decarbonising the Built Environment: a Global Overview, by Tom Ackers

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Globally, the built environment’s greenhouse gas emissions comprise those from construction, and those from the operational use of buildings (for electricity, heating and cooling, cooking, etc).

By weight, building and infrastructure construction creates by far the largest “stock” of materials, globally.

The Heidelberg cement factory, Germany. Source: Heritage calling / Creative Commons

In this part, I look at the historical growth in material stocks (section 5.1); the maintenance and replacement of these stocks (section 5.2); how these stocks have accumulated in different countries (section 5.3); and then the impact of land use on emissions (section 5.4). After that I then turn to the present state of man-made emissions in the built environment (section 5.5). Finally, I outline what I see as the big issues raised by decarbonisation (section 5.6).

5.1. A history of material stocks

Much of the greenhouse gases emitted in the history of the fossil economy is embedded in material stocks of metals, building materials and waste. To quantify the emissions, we need to quantify the scale of these material stocks and the flows that produced them. To do so I will draw on work by a team of researchers mostly based at the Vienna Institute of Social Ecology.

A series of studies shows that, globally, about 1000 billion tonnes (1000 Gt) of physical materials are embedded in buildings and infrastructure. One such study, published in Nature in 2020, was reported with the headline: “Human-made materials now outweigh Earth’s entire biomass”.[1]

London: corporate pressure versus climate action

Review by Simon Pirani of Breathe: tackling the climate emergency, by Sadiq Khan (Hutchinson Heinemann, 2023, 216 pages). First published by The Ecologist

If eloquence and humour were enough to tackle climate change, this book would take us a long way. But it’s very short on honest assessment of the problems, and unvarnished discussion of how to address them … and that, given Sadiq Khan’s reputation as a “climate leader”, is scary.

Khan, now half way through his second term as Mayor of London, traces the “beginning of my journey as a climate activist” to breathing problems he experienced after running the London Marathon in 2014.

XR march in London, January 2023. From Extinction Rebellion Huntingdon facebook page

A diagnosis of adult-onset asthma “made me think about many issues I had never really considered. Had the air we breathed always been this bad? How many people were affected? Was air pollution linked to climate change?” (page 10).

Previously, “I had never been particularly ‘green’”, had driven a Saab convertible and in parliament voted for a third runway at Heathrow. “Climate change had always seemed very far away – both geographically and temporally. […] Asthma made me think again.”

As Labour candidate for Mayor in 2016, Khan reversed his stance on Heathrow, attracting accusations “not just of inconsistency, but political opportunism”. The truth was, he writes, “I had been on a political journey” (page 82). He had met with groups such as the Heathrow Association for the Control of Aircraft Noise (HACAN), who had pointed to the data: 10,000+ premature deaths a year in London from air pollution.

Khan claims credit for bringing together an “eclectic band of activists, local councils and stakeholder groups”, whose campaign against the third runway culminated in a Court of Appeal ruling in 2020 against the government’s decision to proceed. (The project is still on hold.)  

What cutting greenhouse gas emissions actually means in practice

“We have to do things very differently”, transport researcher Jillian Anable told the Royal Meteorological Society’s Climate Change Forum in London last week. “It’s not about celebrating electric vehicles.”

Cars are “getting bigger and heavier”, Anable warned, meaning that “it will take longer to decarbonise the system”. Of new car sales globally, 46% are SUVs.

Architects for Climate Action and Architects Declare joined Fridays for Future to march through London on 23 September. Photo from Architects Declare twitter feed

For every electric car sold, 10-15 large vehicles are sold: they “negate the effect of that electric vehicle many times over”. Moreover, half the electric cars sold are plug-in hybrids, which use “a great deal” of petrol and diesel.

No country has “achieved the speed and scale of reductions [in greenhouse gas emissions] that we now need”, Anable, professor of Transport and Energy at the University of Leeds, said. And no country has “achieved deep and long-term reductions [in transport emissions] without restricting car use.”

Anable was one of several researchers at the Forum who addressed the yawning gap between government declarations about climate change, and the snail’s pace of action – the gap that has infuriated, and motivated, the new generation of protesters from Greta Thunberg to Just Stop Oil.

Transport, the built environment and the food chain – three areas of gigantic fuel consumption – were covered in detail. Adaptation (coping with the effects of climate change) was considered along with mitigation (how to minimise the level of global heating).

Built environment researcher Alice Moncaster launched a broadside against the culture of demolish-and-build, as opposed to retrofitting existing buildings.