Representative image by Rhugved Kandpile from Pixabay

New research by the Potsdam Institute for Climate Impact Research (PIK) in Germany suggests that living in timber cities could avoid emissions.

The new study shows that housing a growing population in homes made of wood rather than conventional steel and concrete could prevent more than 100 billion tonnes of emissions of greenhouse gas CO2 until 2100. These represent about 10 per cent of the carbon budget still available for the 2°C climate target. For the supply of construction wood, newly established timber plantations are necessary in addition to the harvest from natural forests. Even though this has no impact on food production, the scientists warn that if the situation is not carefully managed, biodiversity may suffer.

The study is the first to examine the effects of a widespread switch to timber cities on land use, emissions related to land use change, and long-term carbon sequestration in harvested wood products. It was published in the journal – Nature Communications.

Lead author for the study, Abhijeet Mishra, who is also a scientist from the Potsdam Institute for Climate Impact Research (PIK), said: “More than half the world’s population currently lives in cities, and by 2100 this number will increase significantly. This means more homes will be built with steel and concrete, most of which have a serious carbon footprint”.

“But we have an alternative: We can house the new urban population in mid-rise buildings – that is 4 to 12 stories – made out of wood,” added Abhijeet.

As trees take CO2 from the atmosphere to grow, wood is recognised as a renewable resource with the lowest carbon footprint of any comparable building material. Abhijeet explains, “Production of engineered wood releases much less CO2 than production of steel and cement. Engineered wood also stores carbon, making timber cities a unique long-term carbon sink – by 2100, this could save more than 100Gt of additional CO2 emissions, equivalent to 10 per cent of the remaining carbon budget for the 2°C target.”

The scientists examined four different land-use scenarios for the paper using the open-source global land use allocation model MAgPIE: one with traditional building materials like cement and steel, and three with increased demand for wood on top of the standard demand for wood. They also examined the sources of the additional high demand for wooden building materials and the potential effects on both direct and indirect land-use-related carbon emissions.

Co-author of the study, Florian Humpenoder explained: “Our simulation shows that sufficient wood for new mid-rise urban buildings can be produced without major repercussion on food production.”

“Wood is sourced from timber plantations as well as natural forests. Most of the additional timber plantations needed – we are talking about roughly 140 million hectares – are established on harvested forest areas and thus not at the cost of agricultural land,” as Humpenoder underlines. “We need farmland to grow food for the people – using it to grow trees could potentially cause competition for the limited land resources.”

Increasing forest harvest levels while protecting the most valuable forests

The effects of replacing natural ecosystems with timber plantations on biodiversity were also examined by scientists. Alexander Popp, head of the land use management group at PIK scientist and co-author of the study, explained: “The question of how and from where to source the wood for the construction of timber cities is crucial. In our computer simulations, we have set a clear limit to timber extraction and for adding new tree plantations: Nothing can be cut off in pristine forests and biodiversity conservation areas.”

In fact, Popp underlined: “The explicit safeguarding of these protected areas is key, but still, the establishment of timber plantations at the cost of other non-protected natural areas could thereby further increase a future loss of biodiversity.”

Other research suggests that steps like switching to a vegetarian or vegan diet could help free up land for food and wood production while preserving biodiversity.

Another author of the study, John Schellnhuber said: “The key challenge for global sustainability is the deep co-transformation of land use and construction. If carefully integrated, these two sectors can remove and store crucial amounts of carbon from the atmosphere without jeopardizing food security or biodiversity. This could become the climate solution we have been desperately looking for.”

Galina Churkina (one of the authors of the study) said: “Increasing carbon storage in cities in parallel to land ecosystems is very important for this transition to succeed as a climate change mitigation strategy. Forests have to regrow after harvest and accumulate at least as much carbon as they stored before. The lifespan of timber buildings has to be at least as long as the time needed to repay ‘the carbon debt’ in harvested forests on a sustainable basis.”

Lastly, Abhijeet Mishra concluded: “Our study underlines that urban homes made out of wood could play a vital role in climate change mitigation due to their long-term carbon storage potential. Strong governance and careful planning are required to limit negative impacts on biodiversity and to ensure a sustainable transition to timber cities.”

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