Using more wood for construction has been touted as a lower-emissions alternative to carbon-intensive steel and concrete but it may not be as carbon friendly as thought.
鈥淚t would be very convenient if wood were a better solution,鈥� says at Princeton University. Wood is, in theory, a renewable resource and any wood used in buildings acts as long-term carbon storage. The advent of sturdy engineered-wood products like cross-laminated timber聽has also made it more versatile. Past has found using wood for construction instead of concrete and steel can reduce emissions.
But Searchinger says many of these studies are based on the false premise that harvesting wood is carbon neutral. 鈥淥nly a small percentage of the wood gets into a timber product, and a fraction of that gets into a timber product that can replace concrete and steel in a building,鈥� he says. Efficiencies vary in different countries, but significant amounts of a harvested tree are left to decompose, used in short-lived products like paper or burned for energy, all of which generate emissions.
Advertisement
Many of those emissions may eventually be returned if forests are replanted or they grow elsewhere. But Searchinger says that won鈥檛 fly when we need CO2 out of the atmosphere now. 鈥淥ver a long enough period of time you get a greenhouse gas reduction,鈥� he says. 鈥淏ut in the interim you鈥檝e increased warming.鈥�
Searchinger and his colleagues modelled how using more wood for construction would affect emissions between 2010 and 2050, accounting for the emissions from harvesting the wood. They considered different types of forests and how different fractions of wood going towards construction would change the calculus. They also factored in the emissions savings from replacing concrete and steel.
In some scenarios 鈥� such as in fast-growing plantations in Brazil 鈥� the significant emissions reductions. But each of those cases required what they considered an unrealistic portion of the wood going towards construction, as well as rapid growth only seen in warmer places. Growing more trees might help, but they found land for such plantations isn鈥檛 available, and clearing existing forests would make the problem worse.
In general, they found a large increase in global demand for wood would probably lead to rising emissions for decades. Accounting for emissions in this way, the researchers report in a that increasing forest harvests between 2010 and 2050 would add emissions equivalent to roughly 10 per cent of total annual emissions.
鈥淭he last thing we need is younger forests that store less carbon,鈥� says at Tufts University in Massachusetts, who wasn鈥檛 involved with the research. He says the report highlights that harvesting timber, even when done sustainably, is not a carbon-neutral activity.
But at the National Council for Air and Stream Improvement, a North Carolina-based nonprofit that conducts research for the forestry industry, says he is sceptical of many of the report鈥檚 conclusions. 鈥淚t seems like some of the assumptions in emissions deliberately err on the side of making forest harvest look less desirable,鈥� he says. However, he says it is possible the forest-products industry has overstated the emissions benefits of using more wood.
at Aalto University in Finland says the report鈥檚 conclusions about emissions from rising demand for wood are probably correct, but the story is different for the wood we already harvest. Improving the efficiency of current harvests and using more wood for longer-lived purposes than paper would help reduce emissions, he says.
In Finland, which is a leader in building with engineered wood, Amiri says the forestry industry is experimenting with ways to make engineered wood from smaller trees, and to leave trees growing for longer before harvesting them, for instance. 鈥淲e cannot just say we should stop using wood,鈥� he says.
