Buildings made out of timber could become an important global carbon sink

Timber buildings could store anywhere between 10 million tonnes of carbon per year to 700 million tonnes, according to a new paper published on 27 January in Nature Sustainability.

With anticipated growth in the global population and urbanisation, demands for new housing and commercial buildings will only increase over the next few decades. Around 2.3 billion more people will be living in urban areas by 2050, according to UN estimates. This will place huge demands for the construction of new housing, commercial buildings, and accompanying infrastructure.

The modern world is built on concrete and steel. But cement, steel, and other building materials are a major source of greenhouse gas emissions. Switching to timber materials could potentially turn a significant source of carbon emissions into a powerful carbon sink.

Double benefits of timber

A team of environmentalist and scientists put their heads together to quantify just how powerful timber might prove to be in mitigating climate change. The researchers from the Potsdam Institute for Climate Research (PIK) in Germany and Yale University in the US looked at four different scenarios: business as usual (just 0.5 per cent of new buildings constructed with timber) or driving up timber production by 10 per cent to 50 per cent by 2050. The scientists even suggest that constructing up to 90 per cent of new buildings out of timber is plausible.

Based on their analysis, this could potentially reduce cumulative greenhouse gases emissions from steel and cement manufacturing by one-half, at least, which would contribute to achieving the targets set out in the 2015 Paris agreement. However, under business-as-usual, the construction industry is likely to use up around 20 per cent of the CO2 emissions budget up to 2050.

Furthermore, to reach net-zero carbon emissions, additional carbon sinks are needed to soak up all the carbon from agriculture and other major — and often, less avoidable — sources. Incredibly, a five-story residential building made out of laminated timber, sometimes referred to as mass timber, can store up to 180 kilograms of carbon per square meter. That is three-fold more than the same aboveground mass of natural forest.

The authors write: “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.”

Building timber cities while protecting forests

The researchers also stress that the amount of timber that needs to be harvested — while available in theory — would require sustainable forest management and governance:

“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.”

But if done properly, urban buildings designed with engineered timber could provide long-term storage of carbon and avoid carbon-intensive production of mineral-based construction materials. Co-author Prof Hans Joachim Schellnhuber of PIK said in a statement: “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.“

“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.”

(1) Churkina, G. et al. Buildings as a global carbon sink. Nature Sustainability (2020). DOI: 10.1038/s41893-019-0462-4