By Jay Landers

When it comes to the future, two trends appear likely to come to pass: Global climate patterns will continue to change as a result of increases in carbon emissions and other greenhouse gases, and cities will expand worldwide as a growing number of people migrate to them. In a recent journal article, a group of researchers suggested that the latter could be a partial solution to the former. Namely that the use of engineered wood for newly constructed housing could reduce carbon emissions significantly, as compared with the use of such traditional urban construction materials as concrete and steel.

If 90% of those migrating to cities were to be housed in newly built mid-rise buildings made of engineered wood, 106 Gt of carbon emissions could be saved by 2100, according to the journal article.

Titled “Land use change and carbon emissions of a transformation to timber cities,” the article was published Aug. 30 on the website of the journal Nature Communications. The authors are from the Potsdam Institute for Climate Impact Research in Potsdam, Germany; the Department of Agricultural Economics at Humboldt University of Berlin; and the World Vegetable Center in Taiwan.

‘Long-term carbon sink’

In 2020, the production of concrete, iron, and steel accounted for about 10% of global greenhouse gas emissions, the authors note. Absent a dramatic change in how these materials are developed, future use of these building materials on a large scale will complicate efforts to prevent global temperatures from rising more than 2 C.

“Continuous use of conventional building materials for future infrastructure development could claim 35-60% of the remaining carbon budget associated with limiting the global temperature increase to below 2 C,” according to the article.

Although harvesting timber generates carbon emissions, engineered wood offers a building material that results in far fewer emissions over its lifetime as compared to conventional building materials, the authors say.

“Wood is a renewable resource that usually carries the lowest carbon footprint” of any comparable first-time use building material, according to the article. “Moreover, the carbon stored in wood, which was absorbed from atmospheric CO2 via photosynthesis, is partly preserved when the wood is used as a building material, making it a long-term carbon sink.”

Better than the baseline

For their study, the authors analyzed the likely demand for engineered wood in the construction of wood buildings based on four scenarios:

  • “Business as usual,” in which no buildings made of engineered wood are built for new urban dwellers.
  • “10% timber,” in which 10% of the new urban population will reside in buildings made of engineered wood.
  • “50% timber,” in which 50% of the new urban populace will be housed in engineered wood buildings.
  • “90% timber,” in which 90% of new urban residents will live in engineered wood buildings.

The researchers used what they describe as a “global multiregional open-source land-system model” to examine “future land-use and GHG consequences of using engineered wood predominantly as a building material,” the article states. “The model captures competition for land between agriculture and forestry and accounts for land-related GHG emissions. As such, it allows us to compare long-term carbon storage in (harvested wood products) with emissions from the production of raw materials needed for constructing conventional buildings in the future.”

The modeling results indicated that, compared with the baseline scenario, the 10% timber scenario by 2100 would generate a savings of 14 Gt of overall emissions, or 10% less than the baseline. These savings increased significantly in the scenarios in which demand for engineered wood was higher. In the 50% timber scenario, the savings amounted to 71 Gt of overall emissions, a decline of 51% compared with the baseline. Finally, in the 90% scenario, the emissions savings totaled 106 Gt, or 77% less than the baseline.

“Our analysis compares the emissions from raw material production for conventional building materials and engineered wood, including competition for land and accounts for long-term carbon storage in future wooden buildings,” the article notes.

The study only estimates emissions reductions associated with the construction of new residences for those newly migrating to cities. As a result, the findings likely are somewhat conservative. “If existing buildings, after their serviceable or usable lifetime, would be partly replaced with wooden buildings, the mitigation potential of using engineered wood for construction would likely be higher,” the article notes.

On the other hand, the authors note that their modeling does not account for the possibility that conventional materials could be produced in the future in a manner that results in fewer carbon emissions than is currently the case, which would impact the percentage of savings shown in the article. “This means that, possibly, over time the emission savings will be smaller than indicated by our results,” they state. In fact, various efforts, including recent funding awarded by the U.S. Department of Energy, are underway to research methods for reducing the carbon emissions associated with the production and use of conventional construction materials.

More forests needed

Of course, such a massive shift to the use of engineered wood would necessitate a large-scale expansion on the part of producers. “To meet a considerable portion of engineered wood demand in the future, forest plantation areas would need to expand by more than 200% in the 90% scenario in 2100 compared to 2020,” the article notes. Ultimately, an additional 143 Mha of wood plantations would be needed to meet this increase in demand, according to the article.

If not managed properly, this growth in demand for wood products could potentially damage lands. “The loss of … unprotected ecosystems should not be downplayed as they could have a key role in global carbon cycle variations,” the article states.