June 09, 202 – A milestone peer-reviewed study undertaken by a consortium of European and global trade organizations argues that the underpinnings of the carbon neutrality attributes of bio-based construction products are seriously flawed and do not present an accurate picture of the carbon substitution of the temporary carbon storage benefits of harvested wood building products.
The study, ‘Carbon Accounting for Building Materials – An assessment of Global Warming Potential of biobased construction products,’ was commissioned to review the feasibility of the net-zero carbon economy by 2050 objective of the European Union.
While the focus was on reducing the carbon footprint of the EU’s built environment, the scientific analysis undertaken has global significance and application.
The study notes that the climate change mitigation potential of temporary carbon storage in the built environment has gained increasing attention. It is valid to determine the climate change mitigation potential of harvested wood products (HWP) in construction.
The study’s general conclusion was that from a policy perspective, the EU should not be promoting any type of material over another and should focus on assessing all construction materials in terms of their contribution to the decarbonization of buildings and infrastructures over their whole lifecycle.
The scientific findings behind this seemingly innocuous conclusion represent a seismic impact on the widely promoted assertions that bio-based building products are the simplest and most effective way to contain global warming.
As noted in the study, achieving a net-zero carbon economy by 2050 is one of the critical pillars of the European Green Deal. Choosing the proper policy measures to mitigate climate change requires measuring the Global Warming Potential (GWP) and the environmental impacts across the entire Life Cycle of significant goods and services in the economy.
As the built environment is a significant contributor to greenhouse gas emissions in the EU, it is a primary target for such assessments. Environmental Products Declarations (EPDs) and Product Category Rules are the “building blocks” on which estimates of the climate and ecological impacts of building and infrastructure levels are performed.
Product Category Rules are rules, requirements, and guidelines for developing Environmental Product Declarations for one or more product categories. PRs are particularly useful where the environmental impacts of products within a category group are to be compared.
Such assessments are dependent upon assessing the global warming and environmental impacts of products across their entire life cycle and a full accounting of all carbon emissions. The study notes that the underpinnings of the EU net-zero by 2050 initiative fail on both counts.
An assessment of PCRs and EPDs of wood-based products carried out by the researchers showed that inconsistencies both at the system level of PCR and the implementation in EPDs exist. Ultimately, this results in skewed declared values for biogenic CO2equivalent emissions at the product level and, therefore, in comparison with alternative products.
One of the more contentious issues in the carbon accounting metrics is the principle of the carbon neutrality of bio-based materials. This principle presupposed that carbon lost in the harvesting, manufacturing process, and use of wood-based building products would, in time, be offset by new forest growth that absorbs equivalent amounts of CO2.
However, notes the study, when determining whether a product is carbon neutral through life cycle analysis (LCA), these carbon omissions from material substitution cannot be taken into account as the emissions from other materials do not influence the emissions from the product life cycle.
The study argues that when considering all factors influencing the carbon balance of wood products, the term “carbon neutrality” becomes slightly ambiguous. Therefore, efforts need to include all afore-mention elements of life cycle assessments of wood products (and other biobased materials).
Another fundamental tenet of the EU Net-Zero initiative is the assumption that product substitution of wood for more fossil carbon-intensive building materials will have significant climate mitigation benefits. But the study’s review of the scientific basis of these assumptions suggests that the long-term mitigation benefits related to product substitution may have been overestimated 2- to 100-fold.
These findings underline the importance of the assumptions and starting points for substitution effects in consequential Life Cycle Assessments (LCA).
The study notes that the current general scientific consensus is that when comparing timber products (CLT/GLT) with mineral products (e.g. reinforced concrete and steel), timber products can have a lower contribution to GHG emissions.
It notes that many academic publications using consequential LCA’s on mass timber in construction products reveal considerable variation in methodological choices, particularly on indirect effects, substitution effects, and end-of-life implications.
For example, critical aspects such as the availability of biomass and indirect (allocative) effects remain out of scope with attributional LCA. Consequential LCA has the potential to bring more clarity to these hidden aspects, as the area allows for system expansion.
A recent Intergovernmental Panel on Climate Change (IPCC) report concluded there was only medium confidence that carbon storage in wood products and material substitution can contribute to climate change mitigation when considering sustainably managed forest ecosystems.
In short, not all harvested wood products come from sustainably managed forests; much of the CO2 emitted to the atmosphere from the harvesting and product manufacturing process is not counted for; and most wood products are not recycled at the end of their life due to restrictive building codes, environmental concerns, or costs. As a consequence, they are burnt for energy or left to rot in landfills, where they emit methane, a far more dangerous greenhouse gas.
Within the framework of the reviewed publications here, the study concludes that shifting to using (more) timber for construction can be beneficial to reducing GHG emissions. However, it concludes that without guidelines for consequential LCA, which reduce the variation in methodological choices, the results of these studies remain ambiguous and do not allow such clear-cut conclusions.
It notes a forest system can be either carbon-positive, carbon-neutral, or carbon-negative, depending on the balance between emission, sequestration, and omission processes. In the long term, wood substitution for fossil carbon-based products can be beneficial if carbon uptake outnumbers the emissions from forestry and the production processes of substituted materials do not decarbonize.
However, in the short term, the effects of increased wood use are negligible or may result in net carbon emissions. Increased efficiency and sustainability in the current production processes of other materials such as aluminum, steel and concrete potentially have a more significant impact.
On a final note, the study examined the global warming mitigation potential of carbon stored in harvested wood products in construction with the total GHG emission reduction effort on both a global and European scale.
It concludes that wood used in construction can contribute 0.8% to the GHG emission reduction effort when looking at the global scale and 1.8% at the EU-27 scale. When looking at global warming reduction potential, these numbers translate into 0.02, and 0.002 ºC prevented warming at the global and EU scale.
The global warming reduction potential of harvested wood products in construction is relatively low (0.8%) when considering that the total contribution of buildings to annual global GHG emissions is 21%. This underlines the need for all sectors to move forward on decarbonization strategies.
The full report and executive summary can be found here: www.CA4BM.org. More information on using wood-based building products in the construction sector is available on the Pacific Northwest Building Resilience Coalition website.
