Wood might not be an alternative to concrete: World Resource Institute study

Cement and concrete manufacturing account for around 8% of global greenhouse gas emissions. The iron and steel industry adds another 5 percent. Naturally, the scientific community has been looking for viable alternatives to replace cement and concrete. Particularly, recent years have seen a growing interest in using “mass timber” or structural timber. Mass timber uses technology to stick together pieces of softwood to form larger pieces. As noted in a Vox article, progress in gluing pieces of wood together has also led to more substantial beams and structural panels. Consequently, wood is now suitable for use wood even in tall buildings. Using wood instead of concrete and steel for houses and buildings seemed like a game-changer, and that has been the buzz too. However, new research reveals that there are a lot of other factors to consider before we rely on wood for our carbon-free future.

Tale of a report

A recent report by the World Resources Institute claims that using wood in construction will likely increase emissions for many decades, even relative to using concrete and steel. Moreover, that “mass” timber would require vast additional cutting of the world’s forests. In their report titled The Global Land Squeeze: Managing Growing Competition for Land, Senior Fellow at World Resources Institute Tim Searchinger and his team list some interconnected reasons why turning to more wood for buildings is not a climate-friendly solution. 

Not all harvested wood is utilised

The researchers explain that as a tree grows, it transforms carbon in the air into wood, removing it from the atmosphere and storing it. The argument is that if the whole tree is somehow utilised in making a building (including roots and branches), no carbon will escape into the atmosphere. Hence, there would be no harm to the climate. However, this is different in practice.

The tree bark comprises 10-15% of the wood removed from the forest, which is generally burned or left to decompose by those harvesting wood. Further, when milling logs into lumber, much of the wood becomes small chips or sawdust, some of which are also burned. Some chips and sawdust get turned into paper or wood panels for furniture, which stores carbon longer, but not for decades, as they would in trees. Instead, they are eventually burned or thrown out, leading to decomposition. This way, only a tiny portion of a harvested tree eventually goes into making a building.

The researchers note that these processes emit carbon that would otherwise remain stored if forests were not harvested. 

Harvesting wood is not carbon-neutral

Proponents of wood harvesting say that the activity is “sustainable” as long as the existing carbon stock in the forest remains stable. Sustainability here means that tree growth in other forest areas cancels out the effects of harvesting wood in parts of it. Researchers point out a fundamental flaw in deeming wood harvesting as carbon-neutral. The researchers provide an analogy to explain this:

“Your bank savings account provides a good analogy. If someone removes the amount of money you contribute to it each year or adds by interest, you would be poorer than otherwise because your savings account would never grow. Similarly, harvesting wood makes us poorer in carbon savings because forests would grow more overall and store more carbon if the wood were not being removed.”

This argument aligns with a paper published in Nature which estimated that global wood harvests would add 3.5 to 4.2 billion metric tons of greenhouse gases to the atmosphere annually over the coming decades. That is roughly 10% of annual carbon dioxide emissions in 2022.

Wood harvesting can increase climate warming for decades

Previous research by the same researchers acknowledges the fact that the newly regrowing forests can grow faster than the older, unharvested forests. Studies have previously shown how forests are growing faster everywhere because of climate change. Higher carbon dioxide concentrations in the atmosphere spur tree growth faster, and shorter winters in cold places allow trees to grow longer yearly. 

Pro-harvesters have used this argument to imply that regrowing forests can act as a “payback” to the “carbon debt”. Moreover, they can cover up the carbon lost from previously harvested forests in the long run. However, researchers of this study argue that this eventual payback would mean increased carbon in the atmosphere for many decades until harvested forests catch up to the unharvested forests. Researchers believe that a proper accounting of the effects of wood harvests should indeed be credited for faster regrowth. But at the same time, it should also account for the climate consequences of higher emissions and increased warming for decades.  

Adverse impact on existing forests

Researchers believe that mass timber would affect forests adversely. They project that even without mass timber, the wood used for all purposes other than fuel will be 90% higher in 2050 than in 2010. This translates into roughly 800 million hectares of forests, an area the size of the continental United States. They further claim that any more demand for mass timber is bound to encroach on existing agricultural lands. This is particularly concerning given the ever-expanding demand for the world’s food requirements. Using agricultural lands for forest plantations requires that agricultural lands expand elsewhere. If more forest areas are harvested to meet the demand, widespread and unacceptable losses to biodiversity will be a natural consequence. 

Conclusion

The study concludes that the broad interest in mass timber has relied on incomplete carbon accounting that treats wood as inherently carbon-neutral. It notes that some forest plantations may lead to reduced emissions. However, that would come to be only if some current farmlands were made available for forest plantations. Researchers say this reduction in agricultural land demand would entail an increase in crop yields and reduced meat consumption in high-income countries. They caution that it is dangerous to adopt policies encouraging more human demands for land and its outputs when we are already amid a global land squeeze, growing human demands for food, wood and urban development. “All effort must be put into decreasing this demand, instead,” researchers say.

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