What It Is and How To Reduce It

The paradox of buildings is that they are enormous contributors to climate change long before they’re even built. 

In the world of construction, the conversation around sustainability tends to focus on technologies that increase a building’s resource and energy efficiency, such as geothermal heat pumps, greywater recycling systems, or the transition to solar and wind energy. While these measures are vital, there’s another side of the story that often goes untold, yet is equally essential to healing the negative impacts our buildings have on nature and the Earth’s climate. 

In this article, we will explain what embodied carbon is and explore several strategies and tools for reducing it.  

Let’s dive in.  

JUMP AHEAD: 

1. A Brief Primer on Climate Change 
2. Two Kinds of Emissions: Operational vs Embodied Carbon 
3. What is Embodied Carbon and Why is it Urgent? 
4. The Embodied Carbon Footprint of Concrete 
5. 11 Strategies for Reducing Embodied Carbon 
   1. Reuse Existing Buildings Instead of Constructing New Ones
   2. Use Green Concrete
   3. Use Renewable Building Materials
   4. Reduce, Reuse, and Recycle
   5. Maximize Structural Efficiency
   6. Conduct a Lifecycle Assessment
   7. Pledge to Reduce Embodied Carbon
   8. Buy Clean
   9. Participate in the Development of Product Category Rules (PCRs)
   10. Get Involved with the Carbon Leadership Forum
   11. Use an Inventory Management Platform
6. The Embodied Carbon Toolkit: 5 Resources for Lowering Emissions

The Earth is warming up, leading to a crescendo of catastrophic weather events and the growing threat of planetary ecological collapse. The name of this phenomenon is climate change. While natural records have revealed that the climate has changed multiple times throughout history, the data also shows that the accelerated rate of global warming we are now experiencing is without precedent. 

Past climate change events were caused by slight variations in the Earth’s orbit around the sun, the full effects of which manifest over thousands of years. These so-called Milankovitch cycles cannot account, however, for the sharp hockey-stick 1.1°C rise in global surface temperature that the planet has seen over the last 200 years or so since the dawn of the Industrial Age.  

How then can we explain this striking rise in global temperature? The overwhelming scientific consensus is that climate change is being caused by human activity. Evidence shows that the primary culprit is fossil fuels—the oil, natural gas, and coal that we burn to power modern civilization. When we burn fossil fuels to heat our homes and drive our cars, they emit what scientists call “greenhouse gases,” so named because they trap the sun’s heat within the atmosphere, much like how a greenhouse works. 

The most common greenhouse gas emitted by the burning of fossil fuels is carbon dioxide, or CO2 (also referred to simply as “carbon” for short). The more carbon emitted, the warmer the Earth gets. Right now, the amount of CO2 in the atmosphere is currently 50% higher than pre-industrial levels, according to the National Oceanic Atmospheric Administration. Unless we dramatically lower global CO2 emissions within the next few years, climate scientists predict that the planet will warm by 3°C by the end of this century—a scenario of cascading impacts that would include deep droughts, extensive heatwaves, and rising seas.  

When we think of CO2 emissions, images of smoke-spewing power plants and exhaust-belching automobiles likely leap to mind. What’s perhaps less easy to visualize is how the buildings we live, work, and play in everyday contribute to climate change. Yet buildings are responsible for 39% of total CO2 emissions worldwide, according to the International Energy Agency. 

The carbon emissions from buildings can be broken into two broad categories: Operational and embodied. 

Operational carbon comes from the energy consumed by buildings once they’ve been constructed. In other words, these emissions are a result of the fossil fuels burnt to heat, cool, and electrify our buildings during their lifespan’s. This is the relatively straightforward part of a building’s carbon output that’s both easy to grasp and precisely measure. It’s also most likely what you think of when imagining a building’s carbon footprint. Indeed, you can get a strong (albeit anxiety inducing) sense of a building’s operational CO2 emissions simply by looking at your home’s utility bills every month.  

All told, operational carbon accounts for about 28% of the total building emissions pie.  

The remaining 11% comes from embodied carbon, the greenhouse gasses generated by the complex interplay of building materials, global supply chains, and the construction process from start to finish. 

The combined manufacture of steel and concrete, for instance, emits about 6 billion metric tons of CO2 per year, making up roughly 16% of the world’s annual carbon footprint between them—or about six times the amount produced by the entire aviation industry. The residential construction sector provides another bracing tableau: More than 50 million tons of embodied carbon are emitted by the construction of new homes in the US every year, the equivalent to the annual emissions of entire nations such as Norway, Peru, and Sweden. 

These emissions are alternately referred to as “upfront embodied carbon” or simply “upfront carbon,” as they are generated well before a building is operational. The upfront part of embodied carbon is what makes it such an urgent problem to address. Between now and 2050 is a critical period in human history. Why? Because whatever carbon we do (or preferably don’t) emit over the next few decades will determine whether we meet the Paris Agreement’s goal of limiting global warming to 1.5°C. Embodied carbon may make up a smaller portion of building related emissions, but they are released earlier and more rapidly than operational carbon, contributing more to climate change in the immediate-term. 

The tricky thing is that compared to operational carbon, a structure’s embodied carbon footprint isn’t as easy to quantify or intuitively grasp. Varied material usages, disparate datasets, divergent building techniques, and inconsistent tracking methodologies tend to muddy the waters across companies and from one project to the next. For this reason, embodied carbon often goes overlooked and is sometimes referred to as the “hidden carbon impact” of buildings and the construction industry.  

Anthony Hickling is the managing director of the Carbon Leadership Forum, a non-profit research group at the University of Washington that is a leading advocate for the reduction of embodied carbon on the international stage. 

“Awareness around embodied carbon is not where it needs to be,” Hickling said in a recent interview with the ONE-KEY™ team.  “For decades, ‘green building’ has mostly referred to designing buildings that generate lower emissions through their operations. Only until the last few years have folks started paying notable attention to the emissions associated with the building materials themselves—which are huge. Fortunately, this is gaining traction as a priority for design firms, policy-makers, material developers, and others. But we need a lot more of it.” 

The problem begins with the production process (prior to production, really, if you count the fossil fuels burned to extract and transport all the raw materials involved). One of the main ingredients of traditional concrete is Portland cement, a composite of limestone, gypsum, and this grey stuff called clinker that requires an enormous amount of energy and heat to create: manufacturing a single ton of Portland cement burns about 4.7 million British Thermal Units (BTUs) of fossil fuels, equivalent to roughly 400 pounds of coal. That number takes on sobering proportions when you consider that humans worldwide annually use 30 billion metric tons of concrete, adding 2.9 billion tons of CO2 to the atmosphere every year.  

Much of that carbon is emitted long before ground is even broken on a construction site. Put another way, by the time a single ton of concrete is produced, transported, and poured for the foundations of a new school or apartment complex, the yet to be constructed building has already begun to amass a formidable footprint of embodied carbon. 

Concrete has been a vital building material since ancient times, but if we’re going to continue using it, we need to find a dramatically less carbon-intensive way to manufacture it. Global cement production is set to grow by 12 to 23% between now and 2050, according to projections by the International Energy Agency. To keep global warming below 2°C within that timeframe will require the cement industry to lower its carbon emissions by 24%.  

The following list of strategies is a composite of our own thoughts and recommendations cribbed from the Architecture Institute of America’s “10 Steps to Reducing Embodied Carbon,” the World Green Building Council’s “Bringing Embodied Carbon Upfront” report (2019), and the wealth of resources and toolkits available on the Carbon Leadership Forum’s website.  

Carl Elefante, the former president of the AIA, once said that “The greenest building is the one that is already built.” This elegant turn of phrase can be backed up with concrete numbers: Renovation and adaptive reuse emit as much as 50 to 75% less embodied carbon compared to brand new construction. What’s more, according to a 2016 study by the Preservation Green Lab of the National Trust for Historic Preservation, it can take anywhere between 10 to 80 years to offset the embodied carbon emitted during the construction process of new buildings—even structures that are built to the exacting standards of green building certification systems like LEED or BREEAM. In short, renovating and reusing existing structures is far more eco-friendly than tearing them down and replacing them with new buildings, even green ones.  

The conundrum of concrete is that it is simultaneously one of the world’s largest emitters of CO2 while also being unrivaled in terms of strength and durability. Short of replacing it with something else, what can we do to decarbonize concrete? One solution is to use alternative concrete mixes that substitute clinker with other substances like volcanic ash or use recycled materials to create aggregate. Even better, the industry can more widely adopt Biocement® ,an alternative to Portland cement that is grown instead of manufactured, can heal itself over time, and actually absorbs carbon instead of emitting it. In fact, by embracing readily-available carbon-absorbing materials like mass timber and green concrete, the construction industry can reduce embodied carbon by as much as 60% in as little as two to three years, according to the Carbon Leadership Forum.  

Instead of leaning exclusively on steel and concrete, the construction industry should endeavor to more widely adopt renewable building materials that require less, or even zero carbon to create. There are many great alternatives that occur naturally and can be sourced sustainably, from wood and cork to hemp and mushrooms.  

The three Rs are essential to curbing embodied carbon. A recent report found that construction waste can be reduced by up to 90% by using off-site construction methods.  

Waste can also be minimized by using no more than is absolutely necessary in projects that require carbon intensive materials like steel, concrete, or aluminum. Another easy way to reduced embodied carbon is to use less finishing materials like carpeting, laminate flooring, or decorative tiles.  

Every year, roughly 200,000 buildings are demolished in the US, generating upwards of 600 million tons of waste, according to the Environmental Protection Agency. Instead of burying all that waste in the landfill, AEC professionals should endeavor to reuse it, weaving elements like reclaimed wood into their projects whenever possible. Recycling materials like plastic, aluminum, steel, and concrete is another essential step for minimizing waste and lowering embodied carbon. This is especially critical in the case of steel: as the AIA points out, the embodied carbon footprint of virgin steel can be as much as five times higher than recycled steel. 

Embrace minimalism by maximizing structural efficiency. A building’s embodied carbon footprint is bone deep. Architects and engineers should do their best to design and engineer buildings that minimize the use of carbon-intensive building materials while retaining their structural soundness. An example of this in practice is HAUT, a wooden skyscraper in Amsterdam. Both the foundation and slender internal core of the 21-story residential tower are made of concrete, but the rest of its load-bearing structure is made entirely out of Cross Laminated Timber (CLT), a far more sustainable material. Completed in 2022, HAUT is BREEAM certified and is one of the tallest wooden skyscrapers in the world. Incidentally, Arup, one of the architecture firms that helped design the building, is a signatory to the SE2050 embodied carbon challenge, which we’ll discuss further in a moment.    

A lifecycle assessment (LCA) is a systematic method for quantifying the sustainability of a construction project over the course of its entire lifespan. An LCA provides a complete map of the environmental and climatological impacts of your project, from the embodied carbon related to material extraction to the operational carbon emitted by the structure’s day-to-day power consumption. 

The American Institute of Architects 2030 Commitment, for example, lays out “an actionable climate strategy that gives us a set of standards and goals for reaching net zero emissions in the built environment” by 2030. Inspired by the AIA’s ambition, the Carbon Leadership Forum has issued its own pair of challenges to industry leaders. The result of a partnership with the 30,000 member strong Structural Engineering Institute, the Structural Engineers 2050 Challenge (SE2050) tackles embodied carbon from a structural engineering perspective, providing a toolkit for companies to create their own embodied carbon action plans (ECAPs) and a database where firms can track their embodied carbon emissions. The second challenge, MEP2040, does much the same for mechanical, electrical, and plumbing engineers.  

While a net-zero emissions future remains a distant star on the horizon, these nascent initiatives appear to be making gains. Having seen signatories double over the last five years, the AIA 2030 Commitment now represents 417 firms and more than 56,000 AEC professionals—with more than 20,000 projects between them. Meanwhile, 101 North American structural engineering firms have signed on to SE2050 in the little more than two years of its existence, according to the challenge’s 2022 annual report. All told, firms have submitted a total of 65 ECAPs, or step-by-step outlines for eliminating embodied carbon by 2050. Of that cohort, 60% have launched internal sustainability teams tasked with stewarding their action plans to completion. What’s more, 23% of the SE2050 signatories have reported that they are developing internal tools for conducting ongoing life cycle assessments for their projects. 

If you’re concerned about sustainability in construction, signing on to a pledge like the AIA 2030 Commitment, the SE2050, or MEP2040 challenges can help swing the needle into the green. 

A big reason why embodied carbon is so difficult to track is that much of it passes through what climate experts call “the carbon loophole”—the no-man’s-land between nations where emissions from globally traded goods go unaccounted for as they cross borders. According to the Carbon Leadership Forum, about 25% of global greenhouse gasses are embodied in traded goods that pass through this loophole. One solution for closing it is Buy Clean, a policy framework that incentivizes the use of American-made, lower-carbon construction materials in publicly funded projects. You can learn more about state, federal, and private Buy Clean policies on the Carbon Leadership Forum’s website. 

One way to help lower embodied carbon is to become a decision maker. Product Category Rules (PCRs) is the jargony name for the official criteria used to determine the environmental impacts of different building materials. The kicker is that interested industrial and trade association stakeholders are allowed to vote and observe the PCR development process. To sign up for a PCR committee, visit the website of a program operator like NSF. 

People interested in engaging directly with the issue of embodied carbon can join the Carbon Leadership Forum’s online community, find a local volunteer-led hub, or become a corporate sponsor of the organization’s work. You can also participate in version 2 of the Forum’s Whole Building Life Cycle Assessment Study, a multi-year research project aimed at spurring action on embodied carbon. 

A breathtaking amount of mission-critical materials and assets flow in an out of construction sites everyday. Having to replace assets due to misplacement or theft contributes to waste and adds to a project’s embodied carbon footprint. Thankfully, there’s a wide selection of inventory management software platforms that can help prevent these losses from occurring in the first place. One of them is One-Key, our free and easy-to-use app that enables users to customize, track, and manage entire inventories of tools and equipment.  

• The AIA 2030 Design Data Exchange: A digital tool that enables architects and other AEC professionals to compare the carbon footprints of their projects to industry averages.  

• One Click LCA: Automated life cycle assessment software that helps users calculate the environmental impacts of their projects across their lifecycles.   

• The ICE Database: A free database of over 200 building materials and the embodied carbon emissions they’re associated with.  

• Tally®: An application by Autodesk® for quantifying and analyzing the environmental impact of building materials. 

Bottom Line 

Despite the steady drumbeat of dire warnings, humans activities continue to worsen the climate crisis. Carbon emissions in 2021 spiked by 6%, the single largest annual increase ever recorded. And new research shows that we are on course to breeze past the 1.5°C threshold within the next five years, sending the world’s climate into “uncharted territory.” Still, there are reasons to be optimistic: World governments are finally beginning to invest billions in climate solutions, and while global CO2 emissions continued to rise in 2022, the rate of growth slowed to 0.9%, a mere trickle compared to the previous year. Will carbon emissions continue trending downward in 2023? Can we change before the worst climate change scenarios come to pass? The answer, of course, is up to us. 

Successfully lowering embodied carbon will require the hard work and dedication of everyone in the AEC industry, from material and equipment suppliers to project owners, designers, engineers, construction firms, and contractors. We have the technology, science-backed knowledge, and imaginative capacity to transform how we construct the built environment. The time to act is now.