More than 100 billion tonnes of CO2 emissions could be saved by 2100 if housing construction switches to timber instead of conventional steel and concrete, a new study by the Potsdam Institute for Climate Impact Research (PICIR) shows.
Besides the harvest from natural forests, newly established timber plantations are required for supplying construction wood. While this does not interfere with food production, a loss of biodiversity may occur if not carefully managed.
The study analyses the impacts of a large-scale transition to timber cities on land use, land-use change emissions, and long-term carbon storage in harvested wood products.
“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,” said Abhijeet Mishra, lead author of the study. “But we have an alternative: We can house the new urban population in mid-rise buildings – that is 4 to 12 storeys – made out of wood.”
Wood is known as a renewable resource that carries the lowest carbon footprint of any comparable building material, as the trees take up CO2 from the atmosphere to grow.
“Production of engineered wood releases much less CO2 than production of steel and cement,” Mishra added. “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 looked at four different land-use scenarios: one with conventional building materials like cement and steel, three with additional timber demand on top of the regular timber demand.
They also analysed how the additional high demand for wooden construction materials could be satisfied, where it could come from and what the consequences could be in direct and indirect carbon emissions from land-use.
“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.
“We need farm land to grow food for the people – using it to grow trees could potentially cause competition for the limited land resources.”
The scientists also looked at biodiversity impacts that occur when natural ecosystems are replaced with timber plantations.
Alexander Popp, head of the land use management group at PICIR and co-author of the study, said: “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.”
Other studies indicate that measures such as a transition to healthy diets with less meat consumption could help to release land for wood and food production while conserving biodiversity.
“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,” Mishra concluded.