Embodied carbon is most often used in the context of the built environment, where it is presumed to include emissions from raw material extraction, transportation of materials, materials wasted, building operations and maintenance, and the emissions a building continues to produce after it is no longer in use.
Embodied carbon can be overlooked when considering a building’s (or other product’s) carbon footprint because it is hidden—”embodied,” rather—in materials and manufacturing processes rather than emitted while a product (a building, in this case) is being used.
Here, we explore what is included in embodied carbon, how it differs from operational carbon, its environmental impact, and ways the construction industry can reduce the embodied carbon of their projects for more sustainable development in the future.
What’s the Difference Between Embodied Carbon and Operational Carbon?
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In the context of building and construction, embodied carbon and operational carbon make up the whole carbon life cycle of a building. Embodied carbon is all the carbon that is not emitted through operational processes; operational carbon is the carbon emitted only while the building is being used—which includes the energy needed for lighting, ventilation, temperature regulation, and electricity.
The building and construction sector is solely responsible for 37% of all carbon emissions globally. The United Nations’ 2022 Global Status Report revealed that most of that, 28%, is from operational carbon—meaning only 9% is from embodied carbon. A previous report, however, said that more than 50% of professionals admitted they do not measure embodied carbon in their projects.
While a building’s energy consumption is perhaps more frequently noted than the energy required to build and maintain it, operational and embodied carbon typically make up an equal part of the building’s total carbon emissions.
Examples of Embodied Carbon
Embodied carbon is the sum of CO2 emissions from various manufacturing and construction processes.
1. Raw Material Extraction
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The UN says resource extraction accounts for half the world’s CO2 emissions and more than 90% of its biodiversity loss. The extractive industries included in those figures are two highly in-demand commodities—fossil fuels and biomass (aka food)—in addition to building and construction by way of metal, mineral, and timber extraction. Minerals like sand and gravel are used to produce concrete, and metals are mined for iron, copper, and aluminum building materials. Experts predict that consumption of all these materials will at least double between 2017 and 2060—and that consumption of construction materials, in general, will continue to “dominate resource consumption” for the next several decades.
The most in-demand materials are sand and gravel, which are used to make concrete, sometimes called the most destructive material on Earth—worse, even, than plastic. Concrete’s ability to resist and repel nature is why it’s both so beloved in the industry and so destructive. It not only destroys the most fertile topsoil earth layer and perpetuates flooding, erosion, and pollution via surface runoff; it also refuses to decompose for at least half a century. Yet, it remains the most consumed material (besides water) in the world.
Trees are another story, of course. Deforestation for lumber directly releases sequestered CO2 into the atmosphere and causes habitat loss—sometimes leading to species extinction—which threatens biodiversity on a global scale.
2. Manufacturing of Materials
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Certain construction materials, such as glass and brick, must be manufactured from natural or synthetic resources. Studies have shown that producing a kilogram of bricks—made by packing clay, shale, and/or concrete—generates .16 kilograms of CO2. Glass production—which entails heating limestone, sand, and soda ash using natural gas—is a major air pollutant. The global carbon emissions from glass production alone are estimated at 95 million tons per year. And demand is rising, warns the European Commission, “due to population and infrastructure growth.”
Altogether, construction materials—concrete, steel, glass, brick, aluminum, etc.—represent 9% of all energy-related carbon emissions.
3. Transportation
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Transportation includes the emissions produced during the shipping of construction products to and between building sites.
4. Demolition and Disposal
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A study of construction demolition waste (CDW) broke down the emissions from demolition: from the diesel needed to operate cranes, bulldozers, and other hydraulic equipment to the CO2 emitted from debris during demolition and removal to the tailpipe emissions from transporting the waste. Most building materials—including wood, glass, ceramics, plastic, concrete, and steel—can and should be recycled.
If they aren’t, they end up clogging dumps. The Environmental Protection Agency has said that roughly a quarter of CDW is landfilled, and more than 60% of landfill-bound CDW is asphalt and concrete.
Examples of Embodied Carbon Outside of Construction
Embodied carbon is most associated with construction, but it should also be considered in the context of food (the embodied carbon of processed foods might include emissions from powering the factory, for instance) and transportation (in which tailpipe emissions would be “operational” and emissions from the construction and maintenance of roads “embodied”), among other sectors.
How Is Embodied Carbon Measured?
There are a few ways embodied carbon can be measured, each depending on which materials and/or processes are included in the calculations. All begin at the “cradle,” which is the extraction of raw materials from the earth. Here’s a breakdown of the methodology:
- Cradle-to-gate: The most common measurement, cradle-to-gate embodied carbon is the sum of emissions just from material extraction and production, not from building operations, transportation, demolition, and disposal. This is also called supply-chain carbon.
- Cradle-to-site: Cradle-to-gate plus transportation of materials to the building site.
- Cradle-to-end: Cradle-to-site plus building operations.
- Cradle-to-grave: Cradle-to-end plus maintenance, demolition, and disposal.
- Cradle-to-cradle: Cradle-to-grave plus the carbon emissions from converting the old materials into something new.
Decarbonizing the Building Sector
In its 2022 Global Status Report, the United Nations-backed Global Alliance for Buildings and Construction (GlobalABC) called for decarbonization by 2050. After the pandemic lull of 2020, the industry rebounded negatively, the report said, and buildings constructed since have been manufactured with “increased energy intensity and higher emissions.”
Decarbonizing the building sector would mean phasing out emissions from CO2 and other GHGs until they are removed entirely. Tighter regulations and higher performance standards would put the industry on a pathway to decarbonization.
Ways the industry could reduce embodied carbon emissions include:
- Choosing recycled materials over raw materials in new builds. Recycling a kilogram of aluminum can lead to an emissions reduction of 20 kilograms. Likewise, reusing wood waste can reduce embodied emissions by up to 15%.
- Using responsibly-sourced lumber instead of concrete where possible.
- Continued use and maintenance of old buildings instead of constructing new ones.
- Choosing carbon-sequestering materials like wood or, even more renewable, hemp and straw.
- Demolishing responsibly, salvaging as many building materials as possible to recycle.