‘Timber cities’ could save a billion tonnes of emissions by 2100

·4-min read
Cross laminated timber can be stronger than concrete or steel (Getty)
Cross laminated timber can be stronger than concrete or steel (Getty)

Making new homes out of wood instead of steel and concrete could avoid more than 100 billion tonnes of CO2 being emitted over the next 80 years, and help avoid climate catastrophe, scientists have said.

More timber plantations will be required for supplying construction wood, which could be a risk to biodiversity "if not carefully managed", the experts warned, but wood has a significantly lower carbon footprint than steel and concrete.

The emissions savings from a wide-scale adoption of wood as a construction material in cities would account for around 10 per cent of the world’s remaining carbon budget, scientists at the Potsdam Institute for Climate Research (PIK) said.

The study is the first to analyse 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," said Abhijeet Mishra, a scientist at PIK and lead author of the study.

"This means more homes will be built with steel and concrete, most of which have a serious carbon footprint,” the author continued.

"But we have an alternative: We can house the new urban population in mid-rise buildings – that is four to 12 stories – made out of wood."

The research team said wood carries the lowest carbon footprint of any comparable building material as the trees take up CO2 from the atmosphere to grow, and then it continues to be stored in the building, with timber-based cities becoming long-term carbon sinks.

Engineered wood products include laminated veneer lumber, engineered wooden joists, glued laminated lumber, and cross laminated timber, as well as commonly used wood products such as MDF and oriented stranded board (OSB).

Products such as cross laminated timber and glued laminated lumber derive huge strength and versatility from using numerous layers of bonded wooden boards, and are usually made out of cheaply grown plantation wood, which would be inadequate for construction purposes if cut as conventional lumber.

In order to assess the potential benefit of shifting to wood-based construction, the scientists looked at four different scenarios: One with conventional building materials like cement and steel and three with additional timber demand on top of existing timber demands.

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.

"Our simulation shows that sufficient wood for new mid-rise urban buildings can be produced without major repercussions on food production," said Florian Humpenöder, co-author of the study, and also a scientist at PIK.

"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.

He added: "We need farm land to grow food for the people – using it to grow trees could potentially cause competition for the limited land resources."

However, the scientists suggested that a simultaneous change in human diet – reducing dependency on livestock – could free up more than enough land to allow for new plantations.

Alexander Popp, head of the land use management group at PIK 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."

He added: "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."

Mr Mishra, a PhD student at PIK, added: "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."

The research is published in the journal Nature Communications.