Hi everyone, I’m looking for feedback on biogenic carbon and what we can honestly say about it that is concise, true, and useful. I’ve compiled some thoughts below. You can reply here or email me directly at kanderson@lmnarchitects.com.
Biogenic carbon is very complicated, and not often captured well in current EPD data.
Biogenic materials need to consider both attributional emissions within EPDs as well as consequential emissions that are more difficult to track down. Biogenic carbon can be reported per ISO 21930
Purpose grown biogenic stocks should not compete with food systems for land.
Biogenic carbon usually sums to zero within an attributional cradle to grave analysis, since the end of life scenarios include the release of any stored carbon. This unfortunately devalues the climate impact of storage and …. Most carbon-negative product calculations are cradle-to-gate, showing the carbon they store during their service life. Since there is a time value of storage, we recommend using a discount rate (Post 05) or ton-year accounting (link to Aureus Earth) that will show a benefit for the stored carbon. Direct air capture of carbon that is used within building materials is less likely to re-emit the carbon at the end of life.
Many products sequester more CO2 than they weigh. How? They absorb CO2, release the O2, and store the carbon. Since carbon weighs 3.7 times less than carbon dioxide, a product that is 50% carbon can have sequestered nearly 2x it’s weight in CO2.
Mass Timber. More than 1.5 kg CO2 is sequestered per 1 kg of wood within a final timber product (carbon is stored in wood, residual from breaking up CO2 in photosynthesis). However, forests sequester or emit carbon in the soil and biomass based on forest management; together with logging practices, manufacturing, and transport some forest products have consequential emissions that are very high (similar to steel or concrete structures), and others have significantly negative carbon emissions (link to Ecotrust report).
Agricultural and wood waste can be used to create products that store carbon. These are often short-rotation crops or small diameter wood from the thinning of forests, with wastes that are generally fibers.
Purpose-grown crops for construction materials typically have different accounting than those that are from waste or forest thinning. Purpose-grown crops need to include carbon emissions should include emissions from fertilizers, planting, tilling, and harvesting. With agricultural waste products (and from thinning of forests), these are apportioned, often by dollar value of the products.
For short-rotation crops, carbon is sequestered in roughly the same year the product is produced, so the storage begins immediately. For long-rotation crops such as trees, accounting for when the carbon is sequestered is complicated. From Post 05 (link), we suggest using a discount rate around 3%; for a 60 year life of a mass timber structural system, the carbon storage is equivalent to XXXX.
Location matters. Practices that support biogenic carbon sequestration in one area may not work as well in others.
Context: this is part of a series LMN is doing to explore what carbon neutrality for the built environment means. We are familiar with carbon neutral claims and net zero carbon certifications…but they are all currently missing some things. Here is the table of contents for the ongoing series. Comments above will be compiled into Post 08, Carbon Sequestration Path to Zero Carbon Series - LMN Architects.
Hi, Kjell, good to see you in Seattle! These are all great/useful points, and I think you may find more in chapters 3 and 6 of Build Beyond Zero. (Chris Magwood and Wil Srubar wrote those bits, so I can brag about them unreservedly!) To me, a sort of gist is: Think emergency! That is, store as much carbon as possible in every future building project from now on (including those essential retrofits), as carefully/durably as possible, especially making use of agricultural by-products because that’s stuff we’re growing anyway. If all you’ve got is a rag to plug the hole in the boat, then use the damn rag, stay afloat, and worry later about a more long-lasting fix. My 2 cents, thanks.
To be precise, for wood that is 50% carbon by weight, the CO2e is 1.833x the weight of the wood. Of course, this is best if we are using wood that would otherwise be burnt or composted for putting into building products.
There can be a question on what the timeline for cradle to grave is, but for certain products with lime-based binders, this could potentially be a hundred years, or even 2x or 3x that. To Bruce King’s point, it is going to be much better to store all that biogenic carbon now (rather than releasing it back to the atmosphere) and buy us time while it is stored to bring down the atmospheric carbon content.
I encourage you to check out this list of biogenic carbon resources that my team at WoodWorks just released this week: https://www.woodworks.org/why-wood/sustainability/. These articles aim to answer common questions about biogenic carbon flows over the life cycle in a concise manner that is consistent with ISO standards - including “How to Include Biogenic Carbon in an LCA,” “Carbon Storage in Wood Products,” “Long-Term Biogenic Carbon Storage,” and “Biogenic Carbon Accounting in WBLCA Tools.” Please reach out to us with any questions you have!
This is a really interesting framing of the evaluation of biogenic carbon: what is concise, true, and useful? I appreciate the prompt. In addition to what’s been said before (and perhaps amplifying a few points), here’s what my experience in working with regional biogenic carbon storage solutions has informed (bullet point format to aid in the “concise” part):
We cannot hit our carbon goals without meaningful carbon storage. Doing less harm with low carbon solutions for non-biogenic emission-emitting materials is critical, yet insufficient. We must find meaningful ways to store carbon in order to adequately respond to our sector’s responsibilities in addressing atmospheric emission loading. “Meaningful” certainly implies the depth of nuance to which your list refers - proper accounting, ecosystem service preservation, etc. Carbon storage can’t be an ideal towards which we aspire, but an imperative for which we must design. I appreciate your references to accounting practices that value the time scale of carbon emissions/storage, and how static LCA misses these critical impacts/benefits.
Strategizing for carbon storage requires our orientation as being co-participants in the global carbon cycle. It is our responsibility to understand and amplify existing ecosystem services of photosynthetic carbon drawdown provided by agricultural and silvicultural systems, and ensure their functionality as a result of our investment in these industries to provide us with building materials, not in spite of it. Examples include providing high-value building material product demand to regenerative agricultural enterprises that are more lucrative than global commodity markets, and investing in working forested landscapes under development risk to avoid land use change away from forests. Another adjacent concept: not demanding that forests and fields produce the materials we need for our desired products, but developing products - and buildings - in response to the agricultural and forestry products available for our use while preserving their necessary ecological function of carbon drawdown.
Biogenic materials give us a unique and powerful link from the AEC industry to adjacent industries working to not only reduce their own impact, but amplify drawdown practices. Related to the above, framing our use of carbon storing materials only within the context of managing our industry’s carbon emission accounting misses a much larger and more important system-level intervention; our billions of dollars’ worth of investment power via material consumption can be directed towards industries in need of this investment to improve their practices and further amplify climate benefit beyond carbon storage in aerial plant material through soil building, increased biodiversity, and related regenerative practices. Additionally, investment in land-based agricultural and silvicultural practices have the potential to be investments in regional-scale rural economies that can directly improve the climate impact of these communities via reduced travel time for employment and services, improved efficiency of built infrastructure, etc. Of course, this isn’t a given - multinational corporations that consolidate wealth away from their land base and destroy ecosystems are certainly prevalent within agricultural and forestry - but the potential (and I would argue imperative) for these industries to shift to more socially and ecologically beneficial practices will be greatly facilitated by our industry’s demand for better high-value carbon-storing products from transparent and sustainable supply chains.
To be more concise, we need to store as much carbon as absolutely possible as quickly as possible. Partnering with industries that are already engaged in managing ecosystems that store carbon is one of our best opportunities. How we develop these markets further is of critical importance, as the risk of deforestation and exacerbating the ecological impacts of industrial agriculture looms large. There are 1,000 problems to solve along the way to achieving the potential of this strategy; given the most recent reporting on the current trajectory of global temperature rise, it’s hard to imagine a successful strategy that doesn’t involve biogenic carbon storage in both materials and the development and preservation of soil as an integral part of our work to reach our sector’s climate goals. Not sure how concise that is, but I believe this to be both true and useful
I look forward to reading the next installment of the series!
Just one comment for now:
Hopefully any purpose grown crops for construction materials can be grown through conservation agriculture (no tilling, cover crops, crop rotation/combinations, and very little if any: fertilizer, herbicides, pesticides etc.) Even better, they are crops grown for food but we harvest the “straw”.
Conservation Agriculture repairs soil health and stores carbon in the soil!! Our agricultural system is in trouble too…
This was a great book.
“Growing a Revolution” by David R. Montgomery
I enjoyed your biogenic ruminations and offer some wood-specific thoughts for you:
When wood is used in a building (anywhere) and is eventually a candidate for landfill, there are a couple of landfill designs being proposed that can minimize the loss of carbon to the atmosphere for a long time. One method is called a wood vault wood vault developed and tested at the University of Maryland, and the other is a similar design associated with a CDR design in Australia by InterEarth BiomassBurial. This work shows that wood can sequester carbon for a long time and when paired with responsible forestry, a positive nod to biogenic consideration.
To me this creates a virtuous cycle where the carbon sequestration of wood starts in the forest and continues through the building life and a wood vault, in effect extending the carbon sequestration of trees used in buildings. This concept could also be applied to trees not suitable for use in wood products that are removed for agriculture (i.e. the Amazon).
The recent publication by One Click that surveys eight countries in Europe and presents their current and proposed legislations, states that the Netherlands officially allows biogenic consideration if the carbon is sequestered more that 100 years.
My personal opinion ? Always consider the biogenic aspect of wood but investigate the forestry practice of the sources carefully. Certain mass timber companies are very progressive in their forestry practices to the extent of protecting the carbon sequestration in the ground below the trees as part of their harvesting protocol.
Oh, and design for deconstruction and reuse is a strategy that should be followed whenever possible when using mass timber.
Bob Redwine
Colorado Embodied Carbon Collaborative
It occurs to me that if we sourcing fiber for engineered timber can’t we simply take selective branches and leave the tree growing? This should help maintain the soil carbon that is lost to the atmosphere after logging.
