The term “Global Warming Potential” (GWP) is a measure of greenhouse gas emissions, such as carbon dioxide and methane. These emissions are causing an increase in the absorption of radiation emitted by the Earth, increasing the natural greenhouse effect. This may in turn have adverse impacts on ecosystem health, human health and material welfare.
With regard to buildings, GWP is gauged by carbon emissions and we frequently use a reference of kilograms of carbon dioxide equivalent (kg CO2e).
Operational vs Embodied Carbon Emissions
Design and construction professionals can think of the greenhouse gas emissions from buildings in two basic ways:
- Operational carbon emissions (i.e., its on-going energy use); and
- Embodied carbon emissions from the building’s life-cycle (i.e., everything that went into making the building)
How can operational carbon emissions be measured?
The ongoing energy requirement of a building can be communicated in terms of equivalent greenhouse gas emissions based on a variety of specific factors including total energy consumption over a period of time and fuel-source. We commonly communicate a building’s total annual energy requirement in terms of the Energy Use Intensity (EUI) metric. Such a figure, measured in kBtu/sf/yr can be equated in terms of greenhouse gas emissions using the EPA Greenhouse Gas Equivalencies Calculator (www.epa.gov/energy/greenhouse-gas-equivalencies-calculator), which is a great, easy-to-use resource to help project teams understand the relativity of carbon emissions with regards to energy data input.
What impact are we having from net-zero and energy-efficient buildings on operational carbon emissions?
According to the American Institute of Architects (AIA), the total projected CO2 emissions reduction in 2016 form the efforts of firms enrolled in the 2030 Commitment amount to 16.7 million metric tons of CO2e/yr. According to the EPA Greenhouse Gas Equivalencies Calculator, that’s equivalent to removing 4.9 coal-fired power plants.
Where do we stand with embodied carbon in our buildings?
Architecture 2030 estimates that total greenhouse gas emissions arising from building materials and construction in the US are approximately 6% of the country’s total energy use. These emissions occur at the beginning of a building’s life-cycle.
The University of Washington’s recent Embodied Carbon Benchmark Study compiled a database from a variety of disparate sources and ascertained that over 95 percent of all buildings in the database had an initial embodied carbon of less than 1,000 kgCO2e/m2 (but the study also noted that building typology matters significantly; typically, office buildings ranged from 200-500 and low-rise multifamily residential buildings ranged under 500).
Excerpt from the Embodied Carbon Benchmark Study: LCA for Low Carbon Construction - Part 1
Putting embodied carbon figures into practice
In order to meet the ambitious targets of the Paris Climate Agreement, in addition to driving zero-carbon building operations, the building industry will need to drive to zero embodied carbon. Sound lofty?
According to a recent white paper from the University of Washington and the Massachusetts Institute of Technology, if design team wanted to set targets for embodied carbon reductions over time with a goal of zero by a future date, the value of 1,000 kgCO2e/m2 would represent a reasonable estimate of the maximum embodied carbon in current building practice for the structure, foundations, and building enclosure. This is critical information for design teams engaging in life-cycle assessment (LCA) modeling as it lends a frame of reference for whole-building LCA figures under the global warming potential (GWP) environmental impact category.
This emerging body of work will soon lead to clarified embodied carbon benchmarks that can be used to track and reduce the embodied carbon of our buildings similar to the energy benchmark for Energy Use Intensity (EUI).