Biogenic Carbon Explained
Image courtesy of author.
We learned about it in middle school science class: the earth is comprised of carbon-based lifeforms. However, there is a name for the carbon that all living things embody: biogenic carbon.
Basic of Biogenic Carbon
If we take the ISO (the International Organization for Standardization) definition, biogenic carbon is "produced in natural processes by living organisms but not fossilized or derived from fossil resources." Stated differently, biogenic carbon is "stored" in all living or recently living organismsfrom plants to animals to microorganisms. As such, it is an indispensable part of the carbon cycle.
Consider the example of a tree. Like all photosynthetic organisms, it absorbs carbon dioxide (CO2) from the atmospher— along with water and sunlight— to produce oxygen and energy in the form of sugar (glucose). Through this process, the tree retains carbon in its tissue (i.e., wood) as biogenic carbon. When the tree dies, its tissue decomposes, the biogenic carbon is released, and nature's carbon cycle continues. As such, the tree's carbon may be taken up by other organisms, become stored in the ground, or be released back into the atmosphere.
Another possibility: the tree's tissue (i.e., wood) is harvested as building material and the biogenic carbon embodied in the material is preserved. As the wood is used in building construction, it serves as "storage" for carbon that would otherwise find its way back into the atmosphere via the carbon cycle.
Yet another possibility related to the buildings: biogenic carbon can be used as feedstock for renewable energy sources such as biofuel.
Caveat Regarding Bio-Based Materials
Whether using wood or another bio-based resource for building material or renewable energy, care must be taken to ensure that its lifecycle impacts are beneficial to climate change mitigation as well as ecological and human health. Using the tree example again, deforestation, mismanagement, and unsustainable or improper forestry practices greatly obfuscate the picture for whether or not wood products are a net benefit in any given instance. A rigorous and valid lifecycle assessment is warranted.
Vetting Solutions for Building Design and Construction Professionals
When building design and construction teams are assessing the embodied carbon of a project, it is important to clarify whether or not biogenic carbon is taken into account.
The ability to sequester carbon during its growth allows many bio-based products, such as mass timber, to serve as carbon sequestering alternatives to products with a presumably much higher embodied carbon intensity, such as concrete and steel.
In LCA software, such as Tally and EC3, if users select to incorporate biogenic carbon, the sequestering potential is considered and reported as a negative (good thing) carbon emission. It is generally considered good practice to include biogenic carbon when calculating a building project's embodied carbon. However, teams should clarify when biogenic carbon is incorporated, and it may be prudent to separate biogenic carbon when providing embodied carbon figures (one might liken this notion to separating building energy performance data from on-site renewable energy production data).
We Need Carbon; But We Also Need to Manage It
Carbon is not inherently detrimental to the environment—quite the contrary. The carbon cycle is essential for life as we know it. The challenge we are facing is that an unprecedented level of carbon has become released and suspended in the earth's atmosphere in the form of carbon dioxide, which impedes the expulsion of long-wave thermal energy out of the earth's orbit. The production and function of biogenic carbon is yet another way in which nature offers ecosystem services that we otherwise could not live without.
