Yale: Can Wood Construction Transform Cities From Carbon Source to Carbon Vault?

From Yale University:

Can Wood Construction Transform Cities From Carbon Source to Carbon Vault?

A new Yale study predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production — it could turn the world’s cities into a vast carbon sink.


Writing in the journal Nature Sustainability, a multidisciplinary team of researchers and architects predicts that designing mid-rise urban buildings with engineered timber — rather than relying mainly on carbon-intensive materials — has the potential to create a vast “bank vault” that can store within these buildings 10 to 68 million tons of carbon annually that might otherwise be released into the atmosphere. 
Simultaneously, society would drastically reduce carbon emissions associated with the construction sector, said Galina Churkina, who led the collaborative research while she was a visiting fellow at the Yale School of Forestry & Environmental Studies (F&ES). 
“Since the beginning of the industrial revolution we have been releasing into the atmosphere all of this carbon that had been stored in forests and in the ground,” said Churkina, who is a senior scientist at PIK. “We wanted to show that there can be a vision for returning much of this carbon back into the land.”
Beyond that, achieving a large-scale wood-based construction sector has the potential to create a new “symbiotic relationship” between natural systems and cities, said Alan Organschi, another author, from the Yale School of Architecture and Gray Organschi Architecture in New Haven.
“The city would become a carbon sink rather than a carbon source,” he said. “We would essentially be storing the carbon that would otherwise be combusted for energy or aerobically digested on the forest floor and allowing the forest to ‘continue’ in this restorative, carbon-absorbing system.” 
Other authors include Barbara Reck, a senior research scientist and industrial ecologist at F&ES, Thomas Graedel, professor emeritus of industrial ecology at F&ES, as well as researchers from Potsdam Institute for Climate Impact Research, Tsinghua University’s Department of Earth Systems Science, and Gray Organschi Architecture’s Timber City Research Initiative.

The abstract to the paper ($) summarized in the Yale article:

The anticipated growth and urbanization of the global population over the next several decades will create a vast demand for the construction of new housing, commercial buildings and accompanying infrastructure. The production of cement, steel and other building materials associated with this wave of construction will become a major source of greenhouse gas emissions. Might it be possible to transform this potential threat to the global climate system into a powerful means to mitigate climate change? To answer this provocative question, we explore the potential of mid-rise urban buildings designed with engineered timber to provide long-term storage of carbon and to avoid the carbon-intensive production of mineral-based construction materials.


6 thoughts on “Yale: Can Wood Construction Transform Cities From Carbon Source to Carbon Vault?”

  1. Wood products are a lousy place to store carbon compared to forests, because
    * Trees are longer lived than most buildings. Logging retards the ability of forests to reach their biological potential for carbon storage.
    * Only a small fraction of carbon in logged forests ends up stored in wood products, most of the carbon in logged forests is put on an accelerated path to the atmosphere. For every ton of carbon in buildings, there are several additional tons of C transferred from the logged forest to the atmosphere. So wood products are a net source of carbon, not s net sink.
    * Production of steel and concrete can be decarbonized. Production of wood products cannot be decarbonized.

    “To the extent that management can direct carbon into longer lived pools, it can increase the stores of carbon in the forest sector. Harvest of carbon is one proposed strategy to increase carbon stores. However, harvesting carbon will increase the losses from the forest itself and to increase the overall forest sector carbon store, the lifespan of wood products carbon (including manufacturing losses) would have to exceed that of the forest. Under current practices this is unlikely to be the case. A substantial fraction (25–65%) of harvested carbon is lost to the atmosphere during manufacturing and construction depending on the product type and manufacturing method. The average lifespan of wood buildings is 80 years in the USA, which is determined as the time at which half the wood is no longer in use and either decomposes, burns or, to a lesser extent, is recycled. However, many forest trees have the potential to live hundreds of years (e.g. 800 years in the Pacific northwest USA). Mortality rates of trees are generally low, averaging less than 2% of live mass per year in mature and old forests; for example, in Oregon, mortality rates average 0.35–1.25% in forests that are older than 200 years in the Coast Range and Blue Mountains, respectively [8]. Moreover, the average longevity of dead wood and soil carbon is comparable to that of live trees. When the loss of carbon associated with wood products manufacturing is factored in, it is highly unlikely that harvesting carbon and placing it into wood products will increase carbon stores in the overall forest sector. This explains why in all analyses conducted to date, wood products stores never form the majority of total forest sector stores.” Law, B. & M.E. Harmon 2011. Forest sector carbon management, measurement and verification, and discussion of policy related to mitigation and adaptation of forests to climate change. Carbon Management 2011 2(1). https://content.sierraclub.org/ourwildamerica/sites/content.sierraclub.org.ourwildamerica/files/documents/Law%20and%20Harmon%202011.pdf

    “There are also losses of carbon that occur during the creation of forest products. These losses to decay and wood products make carbon sequestration slower when harvesting is allowed. The young timberlands that replace older harvested lands grow quickly, but hold less in total carbon stores than their older counterparts; the net sequestration from forest products adds to total carbon stores, but does not come close to the vast amounts of carbon stored in non-harvested older timberlands. This finding differs from other papers that have shown that the highest carbon mitigation can be reached when high productivity lands are used exclusively for wood products creation (Marland and Marland, 1992). The wood products considered in these studies were either long lasting or used for fuel purposes. Allowing harvested timber to be allocated to all types of wood products increases carbon emissions and results in no harvest regimes sequestering more carbon.” Alyssa V. Shanks. 2008. Carbon Flux Patterns on U.S. Public Timberlands Under Alternative Timber Harvest Policies. MS Thesis. March 2008. http://ir.library.oregonstate.edu/dspace/bitstream/1957/8326/1/A_Shanks_Thesis_04%2002%2008_final.pdf.

    “[W]ood product usage is reducing the potential annual sink by an average of 21%, suggesting forest carbon storage can become more effective in climate mitigation through reduction in harvest, longer rotations, or more efficient wood product usage. … Allowing forests to reach their biological potential for growth and sequestration, maintaining large trees (Lutz et al 2018), … will remove additional CO2 from the atmosphere. Global vegetation stores of carbon are 50% of their potential including western forests because of harvest activities (Erb et al 2017). Clearly, western forests could do more to address climate change through carbon sequestration if allowed to grow longer.” Tara W Hudiburg, Beverly E Law, William R Moomaw, Mark E Harmon and Jeffrey E Stenzel 2019. Meeting GHG reduction targets requires accounting for all forest sector emissions. 23 August 2019. Environmental Research Letters, Volume 14, Number 9. https://iopscience.iop.org/article/10.1088/1748-9326/ab28bb/pdf.

    “Key Points – 1. When wood is removed from the forest, most of it is lost during processing. The amount lost varies tremendously by region, tree species and size, and local infrastructure. 2. The majority of long-term off-site wood carbon storage occurs in landfills, where decomposing wood gives off significant amounts of methane, a gas with high global warming potential. 3. In addition to wood processing losses, fossil fuels are required to turn raw logs into finished products and ship them from forest to mill to construction site to landfill. 4. Once wood losses and fossil emissions are accounted for, the process of harvesting wood and turning it into products may release more greenhouse gases than the emissions saved by storing carbon in products and landfills. … 9. Properly managed, wood can be a renewable source of building materials and fuels, but solving the climate crisis will require reducing the use of all materials and energy.” The Wilderness Society 2009. Wood Products and Carbon Storage: Can Increased Production Help Solve the Climate Crisis? Washington, D.C. http://web.archive.org/web/20100601080813/http://wilderness.org/files/Wood-Products-and-Carbon-Storage.pdf.

    • Western dry forests could be a lousy place to store carbon especially during climate change, because they can get eaten by insects, die for other reasons and burn up.

      Even west side forest can burn up.

  2. Here we have another battle of science papers. The one mentioned by Yale, Churkina et al, has 83 references, three of which list Bev Law as a coauthor.

    One of the references is to “Carbon, Fossil Fuel, and Biodiversity Mitigation With Wood and Forests,” by Chadwick Dearing Oliver, Nedal T. Nassar, Bruce R. Lippke & James B. McCarter, Journal of Sustainable Forestry, Volume 33, 2014, which notes that:

    “More CO2 can be sequestered synergistically in the products or wood energy and landscape together than in the unharvested landscape. Harvesting sustainably at an optimum stand age will sequester more carbon in the combined products, wood energy, and forest than harvesting sustainably at other ages.”

    I guess we all can pick our own “best available science.”

  3. With the multitude of variations of site-specific conditions and “logging” methods, of course there is no honest and comprehensive study to guide us. There are likely to be synergies not planned for, in various scenarios. For now, we have to go with what educated humans think is best for each particular project. To go along with that, we also need full transparency.

  4. “Harvesting sustainably at an optimum stand age will sequester more carbon in the combined products, wood energy, and forest than harvesting sustainably at other ages.”
    This sound like a “duh” statement; but what is meant by “optimum?” If it means an economic optimum, that would be an overly fortuitous coincidence for it to also be best for carbon. If it means a carbon optimum it dodges the question of when that is (which might be never). (And I wonder what is meant by “sustainably,” but I guess we can assume it means the same thing in both instances so maybe it doesn’t matter.)

    I think the question about substitution is an important one, and I’d like to hear more about “Production of steel and concrete can be decarbonized.”

  5. Absolutely! Using timber as the main building material for inner cities may seem counterintuitive, but novel technologies combined with an overwhelming climate benefit make it something every city planner should consider.


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