How do you measure embodied carbon?
Measuring embodied carbon is a very detailed process that looks at all carbon emitted throughout the life of the product, and the method used is called Life Cycle Assessment.
Life Cycle Assessment (LCA) is the approach used to evaluate the total carbon emissions for the life cycle of a product. Software is available to perform the LCAs and most are integrated into BIM modeling software (e.g. Revit). The most commonly used LCA software is Tally, One Click LCA, and Athena Impact Estimator for Buildings.
In the “What is it?” section there is a detailed example of the Product stage for structural steel. A complete Life Cycle Assessment has five distinct phases: Product, Construction, Use, End-of-Life, and Beyond building life cycle. The chart below shows all of these phase and their stages. There are international standards regulating the data and methods required to determine the embodied carbon in each stage.
Importance of timing of emissions: International climate scientists working for the Intergovernmental Panel on Climate Change (IPCC) have correlated the amount of GHG in the atmosphere with the average global temperature, and they have developed a budget of emissions for various probabilities for limiting the average global temperature to targeted values such as 1.5C. The IPCC recommends reduction for all sources of carbon emissions of 50-65% by 2030 and 100% by 2050 in order to have a 50% chance of reaching a 1.5C goal.
“Upfront” carbon emissions generated in stages A1-A5 occur upon completion of the building, and result in an immediate charge against the carbon budget - these upfront emissions are the most important to reduce. The end-of-life emissions will occur 60-75 years after the building is complete, so buildings built in 2024 would not emit stages C1-C4 carbon until after 2050. If electric powered construction equipment and a 100% renewable energy supply is in place for a 2024 building at the time of stages C1-C4, the emissions at the building’s end of life may be close to zero.