Building new urban homes from wood instead of concrete and steel could save about 10% of the carbon budget needed to limit global heating to 2C this century, according to a new study.
The overhaul of construction practices needed for such a shift would require up to 149m hectares of new timber plantations – and an increase in harvests from unprotected natural forests – but it need not encroach on farmland, according to the paper by the Potsdam Institute for Climate Impact Research (PIK).
Housing 90% of the world’s growing urban population in mid-rise wooden buildings could prevent 106bn tons of carbon emissions by 2100, says the research.
Abhijeet Mishra, the paper’s lead author, said: “More than half the world’s population currently lives in cities and by 2100 the 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 four to 12 storeys – made out of wood.”
The study, published in Nature Communications on Tuesday, is the first to analyse the scale of emissions cuts possible from a large-scale transition to “timber cities”.
Using four different land-use scenarios, PIK scientists used the Magpie open source global land use model to explore the impacts and practicalities of the “timber cities” idea.
Their reasoning was that wood has the lowest carbon footprint of any building material, because the carbon dioxide absorbed during tree growth will not be emitted until the timber is finally destroyed.
Alexander Popp, a co-author of the study, said that preventing logging for timber in pristine forests and biodiversity conservation areas was crucial to their calculations.
“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 further increase a future loss of biodiversity,” he said.
Environmentalists, though, point out that the world’s 131m hectares of tree plantations tend to be less biodiverse than natural forests and burn more easily.
Sini Eräjää, Greenpeace’s European food and forests campaign lead, said it would be “a terrible idea” to cut down natural forests and replace them with wood plantations.
“It would be a disaster for nature and for the climate,” she said. “Natural, biodiverse forests are more resilient to drought, fires and disease, so are a much safer carbon store than the tree plantations we’ve seen go up in smoke this summer from Portugal to California. Wood can play a bigger role in construction but to double the world’s tree plantations at the expense of priceless nature is just bonkers, when modest reductions in meat and dairy farming would free up the land needed.”
Mishra accepted that wildlife loss would occur with tree plantations and called for “strong governance and careful planning to limit negative impacts to biodiversity”.
“Bio-physical risks” such as the potential for city wildfires to become more common had not been assessed in the report, he added.
Wood is still preferred by US house builders but as wildfires have intensified amid worsening climate disruption, some have questioned the practice of building with flammable materials.
Abhilash Panda, the deputy chief of partnerships at the UN Office for Disaster Risk Reduction in Geneva said: ”Wood does provide benefits. It provides a carbon sink, reduces emissions, and provides a way to address unmanaged forests. On the downside, it is flammable. However, what matters the most in determining fire risk is what type of housing is being considered, who is the target and what is the location. Risk is location specific and any design needs to embed resilience in it.”
About 15bn trees are globally felled each year at present. The planet’s tree population is thought to have almost halved since the dawn of human civilisation.
