Why wood use conflicts with climate targets
The climate benefits of storing carbon in wood products and soils are insufficient to counter the carbon losses caused by increased harvesting, SYKE researchers say. As a result, expanding wood use simply does not support climate targets this century.
Increasing the use of wood is unlikely to help meet climate targets within this century. The role of wood-based materials and energy must therefore be reassessed in the EU’s forthcoming bioeconomy strategy, write SYKE researchers Jari Niemi and Sampo Soimakallio.
A recent project examined how increasing or decreasing wood use could affect progress towards the goals of the Paris Agreement. In principle, changes in wood use could contribute to all three key climate mitigation pathways: deep cuts in fossil-based CO2 emissions, maintaining and strengthening the land carbon storage and sink, and scaling up permanent CO2 removal from the atmosphere through geological storage.
However, unavoidable trade-offs mean that these desired outcomes cannot be achieved simultaneously by changing wood use alone.
To assess the carbon impacts of increased wood use, a reference scenario is needed – a “world without increased wood use”. Compared with this scenario, higher wood use reduces forest carbon stocks and carbon sequestration. This reduction can be described as a forest carbon deficit, or carbon debt.
Wood-based carbon storage does not balance forest losses
Increasing wood use can also generate benefits. When carbon is stored in wood products, it does not immediately escape as emissions that would boost climate warming. Carbon can also be stored in soils. These benefits can be described as technosphere carbon credits.
To mitigate climate change, technosphere carbon credits should be higher than the forest carbon debits. Unfortunately, research shows that technosphere carbon credits are far too low to compensate forest carbon debits within this century – the critical period for limiting global warming to well-below two degrees.
Put simply: one additional unit of carbon harvested from forests produces approximately 0.5 units of technosphere carbon credits, but reduces forest carbon stocks by around 1.6 units. The net effect is therefore climate warming. According to research, this holds true over at least a 100-year time horizon. While many assumptions influence the results, none of the uncertainties change the overall conclusion. Technosphere carbon credits cannot compensate for forest carbon debts.
Longer-lived products could improve outcomes
There are further challenges that limit the benefits of storing carbon in wood or soils. Climate policy aims to phase out carbon from all energy and material production. As a result, technosphere carbon benefits decline relatively quickly over time, extending the payback period for forest carbon debts. Climate benefits from wood use could be improved by extending carbon lifetimes – favouring long-lived products over short-lived ones.
The Forest2Value research shows that increasing wood use does not help achieve climate targets within this century. This raises the question of whether wood use should instead be reduced. From a climate perspective, the answer is yes. Reducing wood use would also slow the loss of forest biodiversity and reduce erosion and nutrient runoff.
A key challenge is ensuring that reduced wood use does not increase CO2 emissions from fossil fuels, and that cutting fossil fuel use does not diminish forest carbon stocks. Avoiding these risks requires appropriate and well-designed climate policies. These must simultaneously reduce fossil carbon dioxide emissions, increase permanent CO2 removal, and maintain and strengthen land carbon storage and sinks.
The Finnish Environment Institute SYKE participated in the European ForestValue2 network project, which focuses on the sustainable and diversified use of forest biomass.
Sources
Jari Niemi, Sampo Soimakallio, Elias Hurmekoski, Tanja Myllyviita, Janni Kunttu, Federico Lingua, Tord Snäll: Carbon Credits Through Wood Use: Revisiting the Maximum Potential and Sensitivity to Key Assumptions
Sampo Soimakallio, Hannes Böttcher, Jari Niemi, Fredric Mosley, Sara Turunen, Klaus Josef Hennenberg, Judith Reise, Horst Fehrenbach: Closing an open balance: The impact of increased tree harvest on forest carbon
