A new report presents an ambitious global plan to reduce embodied emissions
To decarbonize the construction sector, a holistic life-cycle approach is necessary, rather than one that solely focuses on operational emissions and ends at demolition
According to the UN Environment Programme, as of 2021, the buildings and construction sector accounted for more than one-third (37%) of global CO2 emissions, making it a significant contributor to climate change.
Efforts to decarbonize the sector have largely concentrated on reducing operational emissions, which arise from the functioning and maintenance of buildings (e.g., heating, cooling, and lighting). Operational emissions currently make up just over two-thirds of the sector’s total carbon footprint and are expected to decrease considerably in the next three decades due to the increasing adoption of renewable energy in electricity grids.
However, operational emissions represent only a part of a building’s carbon footprint. Another significant component is embodied emissions, which are associated with the entire life cycle of building materials. These emissions originate from raw material extraction, product manufacturing (e.g., iron for steel production), construction, and eventual end-of-life (e.g., demolition). Embodied emissions are not evenly distributed, with the majority (65-85%) occurring before construction commences, often in locations far from the construction site due to global supply chains. Reducing embodied emissions is exceptionally challenging due to the scale and complexity of materials production. Additionally, the demand for building materials is increasing as a result of population growth and rapid urbanization, particularly in developing countries. According to the OECD, if current practices continue, global raw material consumption will nearly double by 2060, which could have twice the negative impact on the environment compared to the present. It is not surprising, then, that embodied carbon, also referred to as embedded carbon, is considered the construction industry’s greatest hurdle in achieving net-zero emissions.
A new report, co-published by the UN Environment Programme and the Yale Center for Ecosystems + Architecture, aims to overcome this challenge.
Titled “Building materials and the climate: Constructing a new future”, the report presents an ambitious call-to-action for the buildings and construction industry. While it is not the first document to advocate for urgent decarbonization of the sector, it is arguably the most comprehensive to date. The report involves authors, researchers, and reviewers from six continents, spans 138 pages, and includes approximately 350 references. Needless to say, it explores a far wider range of topics than can be covered in this brief article.*
The report focuses on three strategies, known as the “Avoid-Shift-Improve” framework. The authors suggest that if fully implemented, this approach could enable the sector to achieve net-zero emissions by the middle of this century.
1. AVOID waste and the extraction of new materials by transitioning to a data-driven circular economy that prioritizes material reuse and recycling.
Presently, material economies tend to be linear, following a “take, make, dispose” approach. In a circular economy, the goal is to close the loops of raw materials, emphasizing reduced initial consumption (i.e., reduction), prolonging the usefulness of products (i.e., reuse), and eliminating waste by repeatedly recycling materials. Shifting towards a circular economy necessitates a reevaluation of building design, including the use of renewable or recycled materials during construction and designing for disassembly. Early choices in the design phase offer the greatest potential for reducing a building’s embodied carbon. For existing buildings, retrofitting and renovation should be prioritized as they generate significantly lower emissions (50-75%) compared to new construction.
The use of recycled materials in construction or renovation projects is often restricted by a growing gap between supply and demand. The report suggests that this gap could be bridged by creating enterprises specializing in the careful dismantling of buildings and the storage, preparation, and maintenance of second-cycle materials for resale. Additionally, the adoption of building codes mandating the use of “circular” components made from reusable, renewable materials is deemed necessary. Leadership from national and local governments, as well as collaboration across sectors and borders, is crucial to achieving these objectives.
2. SHIFT towards the use of ethically managed earth- and bio-based building materials.
Wood, a biomaterial with a long history in construction, accounts for 38% of global wood product usage in the built environment. Cross-laminated timber has gained popularity in recent years as a substitute or supplement for steel or concrete in mid-rise buildings, leading to lower embodied emissions. Engineered bamboo also shows promise as a structural material, and waste biomass can be transformed into reconstituted wood products. The overall consumption of processed wood products is projected to grow by 37% by the middle of this century.
The authors contend that the increased use of these materials could result in compounded emission savings of up to 40% by 2050 in many regions, even when compared to low-carbon alternatives such as concrete and steel. However, they caution that a prerequisite for this shift is moving away from the carbon-intensive practices prevalent in forestry and agriculture. Without proper management, a widespread shift to biomaterials could pose risks to natural ecosystems and perpetuate or exacerbate unjust labor practices.
Changing perceptions of different building materials is also necessary. In many regions, concrete, steel, and glass are associated with modernity and progress, despite their limited durability and contribution to the climate crisis by ending up in landfills after a relatively short lifespan.
3. IMPROVE production methods for hard-to-replace materials.
Concrete, steel, and aluminum are the three primary sources of embodied carbon in the buildings sector. Decarbonizing their production methods would be a significant step towards achieving the sector’s net-zero goals.
Cement production, for instance, involves three steps, and the second step – clinker production – offers the greatest potential for emission reductions. Clinker is a key component of cement and is produced by heating limestone and clay to extremely high temperatures. By replacing some of the clinker with alternative materials and using electric kilns powered by renewable energy, carbon emissions from cement can be reduced. The authors also specify that “as much as 25% of emissions from cement and concrete can be easily saved by adapting building codes to incentivize the use of lower-carbon forms” and by promoting the adoption of the best available technologies among architects, engineers, and builders.
In the case of steel, the largest benefits will arise from reducing raw material extraction since producing steel from scrap saves 60-80% energy. The report suggests that transitioning to direct reduced iron technology, which removes oxygen from iron ore without melting it, could reduce CO2 emissions from primary steel production by 61-97% over the next 15-20 years.
Similarly, for aluminum, there is a considerable advantage in using scrap instead of mining ore. In 2019, only 34% of aluminum was produced from scrap, but the authors argue that by 2060, the majority of aluminum production could be based on scrap, with the production process being electrified using renewable energy sources.
This under-construction direct reduction (DRI) plant in Germany is operated with hydrogen and … [+]
The successful implementation of this three-pronged approach hinges on global and cross-sectoral cooperation. The report emphasizes the need to simultaneously support material producers and users (e.g., manufacturers, architects, developers, communities, and building occupants) as they make decisions to decarbonize. Access to reliable and transparent data is crucial for facilitating fair comparisons between different building materials in terms of their embodied, operational, and end-of-life emissions. Such data will also minimize the risk of greenwashing.
The report outlines several policy recommendations and actions, which will vary in their applicability across regions and economies. These include mandating the use of living systems and biomass for urban climate protection, establishing clear and consistent carbon labeling standards, addressing gender pay gaps and improving working conditions, implementing performance-based building codes that consider a material’s environmental impact, and encouraging circular economy approaches to reuse and recycling. In the report’s final section, the authors present case studies of seven countries – Canada, Finland, Ghana, Guatemala, India, Peru, and Senegal – each grappling with unique materials challenges, and discuss how the “Avoid-Shift-Improve” strategy can be applied in their contexts.
In summary, the report proposes a comprehensive reimagining and reordering of urban planning and construction practices. It is an ambitious undertaking that reflects both the urgency and magnitude of the action required to address climate change.
Anna Dyson, Founding Director of Yale CEA and lead author of the report, succinctly captures its essence, stating, “Since the built environment sector is so complex, with interdependencies across actors, all hands on deck are required to decarbonize, and we can’t leave anyone behind. Policies must support the development of new cooperative economic models across the building, forestry, and agricultural industries to galvanize a just transition towards circular, bio-based material economies that can also work synergistically with the conventional material sectors.”
* The report can be accessed for free at buildingmaterialsandclimate.com. I encourage you to read it if you would like to learn more.
