by Christopher Reyer (PIK)
How can forests and their products and services best contribute to climate change mitigation? This is probably the most controversial question one can currently ask when discussing the role of forests to combat climate change – and even scientists tend to disagree here. Some say we should manage our forest and use wood for construction to create a long-term carbon sink. Or produce even more wood to replace plastics and fossil-based materials, which is called circular bioeconomy. Others suggest just the opposite: we should not manage our forests – or if we do, we should not concentrate on wood production but mainly focus on our forests’ potential for biodiversity conservation and carbon sequestration.
All approaches have benefits and trade-offs, considering that our natural resources, including our forests, are limited. That being sad, I would like to focus in this article on the potential of using wood and wood-based products for construction to mitigate climate change, based on a paper on Buildings as a global carbon sink that we – a multidisciplinary group of researchers from Potsdam Institute for Climate Impact Research (PIK) and from Yale University – have published 2020 in Nature Sustainability. When looking at global developments, including discussions at the COP in Glasgow, results from the paper are still very valid – and further scientific and practical exploration is needed, since the world’s population is increasing, and climate change mitigation efforts will be challenged by people’s need for shelter.
Transforming the construction sector
Did you know that buildings and the buildings construction sector combined are responsible for 40% of total direct and indirect CO2 emissions (IEA 2019 Report)? It is obvious that this sector needs to be transformed to mitigate climate change. Research shows that through the use of bio-based construction materials like mass timber and engineered timber products, carbon can be stored. In addition, if more timber is used, this reduces the threat of mining to our environment. For instance, sand mining, which heavily reduces carbon uptake of aquatic ecosystems. Or mining induced deforestation, which was in the case of Brazil alone responsible for 9% of all the Amazon Forest loss in 2005-2015 (Sonter et al. 2017).
In our paper, we created four scenarios of constructing wood use for 2020 to 2050 and found out that buildings made out of engineered timber could store between 10-700 million tons of carbon per year. This would mean cities could become a carbon sink instead of a carbon source.
Four scenarios of timber use to help climate stabilization
In our study we explored these 4 scenarios: Assuming business as usual, just 0.5 percent of new buildings are constructed with timber by 2050. This could be driven up to 10 percent or 50 percent, if mass timber manufacturing increases accordingly. If countries with current low industrialization level also make the transition, even a 90 percent timber scenario is conceivable. Combined with increasing floor areas per capita, this could result in storing between 10 million tons of carbon per year in the lowest scenario and close to 700 million tons in the highest scenario. In addition, constructing timber buildings reduces cumulative emissions of greenhouse gases from steel and cement manufacturing at least by half. This might seem not so much compared to the current amount of roughly 11000 million tons of carbon emissions per year, yet the shift to timber would make quite a difference for achieving the climate stabilization targets of the Paris Agreement.
Importantly, to reach net zero emissions by mid-century, societies need some kind of CO2 sinks to balance remaining hard-to-avoid emissions namely from agriculture.
Buildings could be such a sink – if made from timber. Still, even in the 90 percent timber scenario the carbon accumulated in timber cities over thirty years would sum up to less than one tenth of the overall amount of carbon stored aboveground in forests worldwide.
Sustainable forest management is key
Protecting forests from unsustainable logging and a wide range of other threats is thus key if timber use was to be substantially increased. Our vision for sustainable forest management and governance could indeed improve the situation for forests worldwide as they can be part of regional value chains. Our study showed clearly that we can mitigate climate change by substantially increasing the use of engineered timber for construction worldwide. However, this can only work if enough wood is available and produced in climate resilient forests. When looking at recent forest disturbances like storm or fire damage worldwide, or thousands of hectares being salvage-cut due to bark-beetle infestation in Europe, we realize that the availability of the wood is a crucial point. Furthermore, we need critical investment into sustainable forest management and re-forestation to prevent over-exploitation of forest resources and ecosystems.
In our study we summarized multiple lines of evidence from official harvest statistics to complex simulation modelling to find that, theoretically, unexploited wood harvest potentials would cover the demand of the 10 percent timber scenario. It might even cover the demand of the 50 and 90 percent timber scenario if the floor area per person in buildings worldwide would not increase but stay at the current average. There’s quite some uncertainty involved, yet it seems very worth exploring. Additionally, forest plantations would be needed to cover a large share of the demand, including the cultivation of fast-growing Bamboo by small-scale landowners in tropical and subtropical regions. Here the competition with other land use and the carbon stored in the land that is displaced to increase plantation area is crucial.
Reducing the use of roundwood for fuel – currently roughly half of the roundwood harvest is burnt, also adding to emissions – would make more of it available for building with engineered timber. Moreover, re-using wood from demolished buildings can add to the supply.
To conclude, we need a tight coupling of sustainable forest management and sustainable governance as well as climate, biodiversity, trade and energy policies that sets the rules, criteria, and indicators to support increased building with timber. It is important to note that our analyses exclude protected areas as a source of wood, yet to fully implement our proposal, more work is needed to understand and quantify the risks to global forests.
Finally, I need to mention that we did not consider in our calculation emissions from harvesting, nor reduced carbon uptake from “missing growth” in the forest as well as carbon uptake through regrowth. In future scenarios, these should be taken into account.
Information on the author: Christopher Reyer is leading the working group on “Forest and Ecosystem Resilience” at Potsdam Institute for Climate Impact Research. Together with EFI, he is also a project partner in the I-Maestro project, where Christopher and his team are working on the simulation of management strategies and provision of ecosystemic services at different scales.
Some information in this blog post have been taken from the Press Release on the paper, published by PIK: Buildings can become a global CO2 sink if made out of wood instead of cement and steel — Potsdam Institute for Climate Impact Research (pik-potsdam.de)