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22 / BUILDING DIALOGUE / March 2020 Embodied Carbon: Rising Contributor of Atmospheric CO 2 T he global buildings sector is growing at unprecedented rates, and it will contin- ue to do so. Over the next 40 years, the world is expected to build 2.5 trillion square feet in newconstruction – adding the equivalent of 50 NewYork cities! Meanwhile, government researchers announced inmid-January that the past decadewas the hottest on record, the latest sign of global warming’s grip on the planet. And 2019 was the second-warmest year ever, they said, just shy of the record set in 2016. A key takeaway from the first article in this series was: Curbing embodied energy of building materials is the next frontier if we are to meet carbon reduction goals as set forth in the 2015 Paris Agreement and pre- vent theworst effects of climate change. As crucial as operational energy (the focus of the first two articles) is, it’s not enough: We also need to pay attention to the greenhouse gases that are emitted to construct our buildings in the first place – the embod- ied carbon, which is another significant and rising con- tributor of atmospheric CO2. Embodied carbonwill be responsible for almost half of the total of new construction emissions between now and 2050. Unlike operational carbon emissions, which can be reduced over time with building energy efficiency renovations and the use of renewable ener- gy, embodied carbon emissions are locked in place as soonasabuilding isbuilt. It is critical thatweget ahan- dle on embodied carbon now if we hope to phase out fossil fuel emissions by the year 2050. What is embodiedenergyandhowis it computed? It is the energy expended tomake a building. The building industry today is wasteful and pays lit- tle attention to the limits of materials and resources. Life-cycleassessment (alsoknownas life-cycleanalysis, ecobalance and cradle-to-grave analysis) is a technique toassessenvironmental impactsandcarbonemissions associated with all the stages of a product’s life – from rawmaterial extraction through materials processing, manufacture, distribution, use, repair and mainte- nance, and disposal or recycling. The best way to get a really clear picture of howonematerial or systemcom- pares to another in the context of a building project is to use whole-building life-cycle assessment (WBLCA). Although WBLCA requires specialized software and training, the good news is that these software are de- signed to be used by building professionals. Embodied carbon tools: Athena Impact Estimator, One Click LCA and Tally. These powerful tools produce a full life-cycle model of a building drawn from under- lying LCA datasets. The datasets need to be accurate in order for the results to be meaningful, and developers all use their ownmethodology for producing them. The Impact Estimator is developed by the nonprofit Athena Sustainable Materials Institute and is offered for free as part of Athena’s mission. Much of Athena’s focus over the last decades has been on developing a robust, accurate LCAdataset for theU.S. andCanada. It’s also highly regionalized, whichmeans that users enter their nearest city and get very accurate LCA data based on their regional electrical grid and average transporta- tion distances for all materials. Initially released in 2010 as 360optimi, One Click LCA is used primarily in Europe. But its developer, Bionova, is trying to get a stronger foothold in the U.S. One fea- ture of One Click is that it’s part of awhole suite of inte- grated software tools that cover such things as life-cy- cle costing and circular economy. The biggest selling point of Tally is that it comes to architects in their native habitat. Developed by Kier- anTimberlake, the program is a Revit plug-in and gets all its data inputs directly from the Revit model. Tally’s WBLCA capabilities are supported by an underlying da- tabase developed by thinkstep – a world leader in the LCA field. That dataset is based on North American av- erages (it’s not regionalized like the Impact Estimator). However, sophisticated users can customize certain inputs – for example, if they know a material will be locally sourced and want to change the transportation distance for thatmaterial. Is embodied carbon different from embodied en- ergy? Even though these terms are often used inter- changeably, they are different as energy is “cleaner” in some regions than others. For example, electricity in the Pacific Northwest is predominantly generated using hydropower whereas electricity in Nebraska comesmostly fromcoal. Even though it takes the same amount of energy to produce steel in either location, steel sourced from Nucor’s plant in Norfolk, Nebraska, can have up to seven times the embodied carbon than if it came fromtheir plant in Seattle. Where building products come from is key and em- bodied carbon (expressed as tons of CO2e) is a better measure than embodied energy. What about energy codes and green building pro- grams? Current building energy codes donot address it andupuntil LEEDv4, USGBCdidnot address embodied carboneither. Thenewvisionformaterialsandresourc- es in the built environment comprises three strategies: reduce embodied carbon; protect human and ecologi- cal health; and advance the circular economy. This no doubt will raise awareness about embodied carbon in the building industry. However, it is not a prerequisite, Mohit Mehta, LEED AP BD+C Principal/ Building Performance Director, ME Engineers It’s All About the Carbon