According to a new study, climate stabilization can gain two-fold benefits from a material revolution, in which steel and cement are replaced by wood in urban construction.
First, such a revolution can prevent the emission of greenhouse gases resulting from the production of steel and cement. Second, it can convert buildings into a carbon sink since they preserve the atmospheric CO2 taken up by trees, which, in turn, is harvested and utilized as engineered timber.
But according to the international team of authors, while the needed amount of timber harvest exists at the theoretical level, an upscaling like that would evidently require sustainable and extremely careful management and governance of forests.
Urbanization and population growth will create a vast demand for the construction of new housing and commercial buildings—hence the production of cement and steel will remain a major source of greenhouse gas emissions unless appropriately addressed.
Galina Churkina, Study Lead Author, Potsdam Institute for Climate Impact Research
Churkina continued, “Yet, this risk for the global climate system could be transformed into a powerful means to mitigate climate change by substantially increasing the use of engineered timber for construction worldwide.”
“Our analysis reveals, that this potential can be realized under two conditions. First, the harvested forests are sustainably managed. Second, wood from demolished timber buildings is preserved on land in various forms,” she further added.
Churkina is also affiliated to the Yale School of Forestry and Environmental Studies in the United States.
Four Scenarios of Timber Use to Help Climate Stabilization
The researchers have predicted four kinds of scenarios for the next three decades. Considering business as usual, only 0.5% of new buildings will be built with timber by 2050. If large-scale timber manufacturing continues to increase accordingly, then this estimated percentage can be pushed up to 10% or 50%.
The researchers added that if nations with present low industrialization level also make the shift from traditional building materials to timber, then even 90% timber is possible.
This can potentially result in storing almost 700 million tons per year in the highest scenario and around 10 million tons of carbon in the lowest scenario. Construction of timber buildings also decreases the cumulative emissions of greenhouse gases, produced by the manufacture of cement and steel, at least by 50%.
While this may appear to be relatively less when compared to the prevalent amount of about 11,000 million tons of carbon emissions that occur every year, the transition to timber can make a huge difference in realizing the climate stabilization goals of the Paris agreement.
If building construction continues with steel and concrete, and if there is a rise in the floor area for each person, considering previous trends, then the cumulative emissions of CO2 produced from mineral-based construction materials may reach up to one-fifth of the CO2 emissions budget by 2050—a budget that must not be crossed if warming has to be maintained much below the 2 °C as pledged by governments in the Paris agreement.
Most significantly, to achieve net-zero emissions by 2050, societies require some kind of CO2 sinks to offset the remaining CO2 emissions resulting from agriculture, which are difficult to avoid.
Buildings constructed from timber can serve as such a CO2 sink. Up to 180 kg of carbon per square meter can be stored by a five-story residential building. This value is three times more when compared to the above-ground biomass of natural forests that have a high concentration of carbon.
But even in the 90% timber situation, the carbon built up in timber cities over a period of three decades would still sum up to below one-tenth of the total amount of carbon preserved above the ground in forests across the world.
Protecting Forests from Unsustainable Logging is Key
Protecting forests from unsustainable logging and a wide range of other threats is thus key if timber use was to be substantially increased. Our vision for sustainable forest management and governance could indeed improve the situation for forests worldwide as they are valued more.
Christopher Reyer, Study Co-Author, Potsdam Institute for Climate Impact Research
The researchers summed up numerous lines of proof ranging from intricate simulation modeling to official harvest statistics to determine that, at the theoretical level, the demand of the 10% timber scenario can be met by the unexploited wood harvest potentials.
Unexploited wood harvest potentials may even cover the demand of the 50% and 90% timber scenario if the floor area for each person in buildings across the world does not rise but continues to remain at the present average.
“There’s quite some uncertainty involved, yet it seems very worth exploring,” added Reyer. “Additionally, plantations would be needed to cover the demand, including the cultivation of fast-growing Bamboo by small-scale landowners in tropical and subtropical regions.”
Minimizing the use of roundwood needed for fuel would make it more available for constructing buildings with engineered timber. At present, about 50% of the roundwood harvest is burnt, which also adds to CO2 emissions. Recycling of wood from demolished buildings can also add to the supply.
The Technology of Trees—“To Build a Safe Home on Earth”
As a building material, timber has several fascinating features that have been described in the study. For example, huge structural timbers are relatively resistant to fire—the inner core of the structural timbers is protected by a charring layer upon burning; hence, the timbers are not easily destroyed by a fire.
This concept does not correlate with well-known assumptions based on fires occurring in light-frame buildings. These factors have already been recognized by several national building codes.
Trees offer us a technology of unparalleled perfection. They take CO2 out of our atmosphere and smoothly transform it into oxygen for us to breathe and carbon in their trunks for us to use. There’s no safer way of storing carbon I can think of.
Hans Joachim Schellnhuber, Study Co-Author and Director Emeritus, Potsdam Institute for Climate Impact Research
Schellnhuber continued “Societies have made good use of wood for buildings for many centuries, yet now the challenge of climate stabilization calls for a very serious upscaling. If we engineer the wood into modern building materials and smartly manage harvest and construction, we humans can build ourselves a safe home on Earth.”