An Exploration of Embodied Carbon

Carbon is often referenced in relation to climate change—it’s a buzzword that appears on news alerts about rising temperatures, carbon taxes, and energy plans. Carbon has come to be shorthand for carbon dioxide (CO2), a colorless, odorless gas that is released into the atmosphere when we burn fossil fuels like coal, oil, and natural gas, as well as through respiration. Carbon dioxide is also among the world’s most abundant greenhouse gas (GHG), and the gas that remains in the atmosphere the longest—anywhere from decades to thousands of years. Once it’s in the atmosphere, it absorbs heat and contributes to climate change.

Carbon dioxide has proliferated exponentially in the atmosphere since the industrial revolution in the mid 1800s, when we shifted to machine manufacturing and the burning of fossil fuels. Atmospheric and climatic changes that without human interference occur over tens of thousands of years transpired in less than two centuries. Today, buildings and construction account for 40-percent of the world’s greenhouse gas emissions.

This is where designers, architects, manufacturers and other building professionals come in. These industries are in a unique position to change this trajectory by reducing, neutralizing, and even reversing their carbon footprint. This article will provide a primer in one of the most important problem areas, which is also one of the most significant opportunities for improvement: embodied carbon.

What is embodied carbon?

The carbon emissions of buildings can be divided into two types: operational and embodied. Operational carbon refers to CO2 emissions during a building’s in-use phase—the energy expended through heating, cooling, and electricity. Operational carbon represents 28 percent of global greenhouse gas emissions. Embodied carbon is the CO2 released throughout the extraction, manufacturing, production, transportation, installation, maintenance, and disposal of building materials. The majority of embodied carbon emissions come from the use of fossil fuels to extract and manufacture construction materials, and from manufacturing process emissions. According to recent data from the United Nations Environment Programme, embodied carbon accounts for 11 percent of the world’s greenhouse gas emissions.

Even though operational carbon represents a greater percentage of total emissions, embodied carbon is just as crucial. That’s because sustainable design has adopted strategies that focus on tackling operational carbon by building new, highly efficient buildings powered by renewable energy sources, and by using relatively high-embodied carbon materials to offset long-term operational emissions. The issue with this strategy is that new construction generates a lot of emissions. And there’s no pause button for new construction—in the United States, approximately 5.7 billion square feet of new buildings are constructed each year, with about 300 million metric tons of expected embodied emissions. Even if operational carbon is reduced significantly, with the construction of more energy-efficient buildings, over the next 20 years embodied emissions will surpass operating emissions.

How can embodied emissions be reduced?

There are a number of strategies that can be implemented to scale down embodied carbon in building projects. Here are six of the most far-reaching:

  1. Assess embodied carbon and set goals for each project. This can help with identifying “hot spots,” systems and materials that drive up a project’s embodied emissions and develop strategies to reduce or replace them with less harmful alternatives. The Bath Inventory of Carbon and Energy (ICE) and the Quartz database are two (of many) free resources that provide environmental and health data on common building materials. Design teams can also look for Environmental Product Declarations (EPDs) and other transparency documentation. But perhaps the most thorough tool for assessing embodied carbon is life cycle assessment (LCA), which measures the inputs, outputs, and potential environmental impacts of products or systems across their entire life cycle. While material or building life cycles are often measured from cradle to gate (factory) or cradle to grave (end of use), it is also vital to consider what will happen at the end of a building’s life, before it has been built. This means designing buildings that contemplate future uses, in which systems and materials can be deconstructed and reused in other buildings.
  2. Focus on reducing high-volume and high-emission materials. The majority of embodied emissions (between 50-75 percent) come from the concrete and steel used in the foundation and structure. Concrete—specifically the production of cement for concrete—is the number one material source of greenhouse gases. And even in small amounts, materials like aluminum and certain kinds of foam insulation can have huge footprints. Reducing or eliminating these materials can significantly mitigate a building’s total embodied carbon emissions.
  3. Choose building materials with a low embodied carbon footprint. When possible, choose wood structures over steel and concrete and wood siding over vinyl. Wood usually is responsible for much less embodied emissions than steel or concrete over its lifetime, because forests sequester carbon dioxide. But improperly sourced wood can minimize its benefits from 20-60 percent. Finishing materials are also sources of embodied emissions, so try to leave them out and keep the exposed wood and concrete.
  4. Reuse and recycle materials, buildings, and material waste. Before designing a new building, consider the viability of reusing or retrofitting, which generate much less emissions than new construction. When possible, reuse the foundation and structure, where most of a building’s embodied carbon is held. Renovating and reusing buildings can save 50 to 75 percent of the embodied carbon that new constructions release. And try to use salvaged materials like bricks, metals, concrete, and wood, which would have a high footprint if newly manufactured.
  5. Offset what can’t be eliminated. After doing everything possible to reduce a project’s embodied emissions, the amount of carbon dioxide being produced can be calculated and an offset can be purchased. Carbon offsets compensate for emissions made elsewhere, usually by funding projects that remove carbon from the atmosphere or preventing it from being released in the first place. Some aspects of and manufacturing processes in the life cycle are nearly impossible to fully eliminate, so offsets provide a way for projects to achieve net zero carbon.
  6. Discuss with partners and suppliers. Have conversations about embodied carbon, share resources and perspectives, reflect, and ask collaborators about their strategies. Get creative! There’s a lot to do, and it’s essential to get started right now.

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