More Building Matters
It is conventional wisdom that building with wood has lower carbon emissions than building with steel or concrete. In this post, Dr. Stephanie Taylor, MD, wrote, “If buildings are constructed of wood, not only are the emissions from manufacturing steel and other building materials reduced, the innate carbon-storing property of wood is utilized to benefit decarbonization of the outdoor atmosphere.”
There has long been debate about how much carbon is stored or sequestered in wood construction; much depends on how much of a tree actually makes it from the forest to the mill to the building. But the consensus, according to the Mass Timber Report, is that “When wood is chosen over steel or concrete building materials, the net effect is a reduction in fossil fuel use.” The rule of thumb is that a cubic meter of wood sequesters a ton of carbon dioxide (CO2).
Another take
However, a new study and report challenges the conventional wisdom. The study, The carbon costs of global wood harvests, claims that we should not consider the carbon to be sequestered in the building, because “the forest growth and regrowth used to offset the effects of new harvests would happen anyway.” In other words, the tree in the forest is already storing the carbon, chopping it down stops the process, and turning it into mass timber doesn’t magically store new carbon.
The authors of the study, led by Tim Searchinger of Princeton University, have also written a report, The Global Land Squeeze: Managing Growing Competition for Land for the World Resources Institute (WRI), as well as a summary with the controversial headline, Wood is Not the Climate-Friendly Building Material Some Claim it to Be. I shared their work on Linkedin; the resulting comments range from “It’s utter bollocks” to “I’m with most of…
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4 Comments
Lloyd,
An interesting and definitely thought provoking blog. The accounting is complex, (and I'll admit well beyond me) but one thing that has always troubled me about the arguments around the benefit of sequestering carbon (wood) in buildings is their relatively short lifespan. Isn't there a good chance that the building will be demolished and the carbon released well before the tree would have died and released it into the forest? That of course presupposes that we will, as Searchinger hopes, leave more forests alone.
Some say that a building has to last 50 years to claim that it is storing carbon, because that is the harvest cycle. I think any replacement of steel or concrete is good, and am just saying we shouldn't promise the earth.
https://www.istructe.org/IStructE/media/Public/TSE-Archive/2021/Timber-and-carbon-sequestration.pdf
"and am just saying we shouldn't promise the earth."
Yes, it's messy. I don't see any magic solutions.
"avoided emissions from other carbon-intensive products such as concrete and steel."
This has always seemed like the big win for wood to me. On the sequestration side, it depends on the state of the forest pre and post cut, and also how light of an impact the operation had on soils, etc. I have read a few papers on what state of forest absorbs the most co2 (late succession, old growth, recently thinned, clear cut/patch cut, etc.) and the papers didn't all agree. It's not obvious or easy to know. Some stands can certainly be thinned to improve stocking though. Other operations could certainly increase rotation times.
https://www.sightline.org/series/forest-rotations/
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