Revisiting Wood and Embodied Carbon
January 7, 2019
By Dave Atkins and Sarah Larsen
Paula Melton’s article on The Urgency of Embodied Carbon and What You Can Do About It couldn’t be more timely given the recent Fourth National Climate Assessment and the latest from the Intergovernmental Panel on Climate Change. Embodied carbon is spent immediately, while operational carbon is spread out over the life of a building. We have ten years to mitigate the impacts of climate change—whereas the 100 years of operational carbon will be reduced by growing efficiency and renewable energy.
Unfortunately, there are several points in her article which may undermine this goal. By referencing a recent paper (“Land use strategies to mitigate climate change in carbon-dense temperate forests”) that claims that Oregon’s forest products are the state’s largest emitter of carbon, she lends credence to a flawed study and implies a high degree of uncertainty regarding the sustainability of building with wood.
The Harmon paper is based upon flawed assumptions that dramatically skew the results and make the conclusions unreliable. Why is this so important? In much the same way that a falsely reported link between autism and vaccinations led to the “anti-vax” movement, the results of this information could lead to misguided decisions about forests and buildings at a time when this is most costly. The list of biased assumptions is long, and you can read a full analysis at Treesource.org.
The paper asserts its claims based upon a life-cycle assessment (LCA) process that doesn’t follow the standards established by the International Organization for Standardization (ISO). For instance, the ISO protocol uses 75 years for the average life of a building. The Harmon paper uses 30 years, a decision which significantly undermines the ability of structures to store carbon. The paper uses a 2% deconstruction rate for new buildings beginning the year after completion and applies that 2% as a degradation for the carbon energy avoided by using wood in our buildings. Not one of four LCA experts consulted said this was appropriate.
Further problems arise in the way the researchers modeled forest management and resulting carbon storage. Private production forests in western Oregon typically operate on a 40- to 45-year rotation from planting through growth to harvest. In order to support their advocacy of 80-year rotation limits, the writers provided for zero “leakage” in their model. Leakage is the trade-off made when there is increased harvest elsewhere to meet demand for wood products. It is unreasonable to suppose that wood from other places (or materials with higher carbon impacts) wouldn’t be used instead. Additionally, they underestimated forest fires when there is a clear trend for larger fires and longer fire seasons, which is forecast to worsen.
The Harmon paper aside, Melton’s article expresses uncertainty around the carbon benefits of wood if it isn’t grown sustainably. In the U.S. and Canada, there are hundreds of millions of sustainably certified timber-producing forest acres. There are millions more of federal and state lands, mandated by law to be sustainably managed at standards that meet or exceed certification. The U.S. Forest Service maintains a national inventory of all forested lands. For more than 50 years, our forests have been sequestering 11%–14% of annual fossil carbon emissions because in the U.S. we grow more than we lose—either through harvest or through trees killed by wildfires, disease, or insects. North America and western Europe have the highest per capita wood use globally, yet grow more trees than they harvest. The unfortunate reality is that the U.S. national forests have 70 to 80 million over-crowded acres needing a blend of planned burning and harvests to make them sustainable. Creating markets for wood from small- and medium-size trees to replace products based on fossil carbon sources like plastics and concrete is needed to create more resilient forests and sustainable practices in a changing climate.
Another uncertainty referenced is a 2010 study for the state of Massachusetts. Sadly, this perpetuates a myth that wood energy is worse than coal. It included a hypothetical harvest of a 100-year-old forest where 100% of the wood was used solely for electricity production, which is only 25%–30% efficient. In reality, this is never done. Any tree sizable enough to be run through a mill to make lumber for construction, flooring, furniture, paper, or packaging has more value as fuel for energy. Only a fool would implement this scenario. When properly implemented, use of wood for energy is quite efficient and can be scaled for use in residential, commercial, district energy production and industrial grid electricity.
It is crucial that buildings have optimized material choices to reduce embodied energy. All materials have unique qualities that make them desirable for aesthetic, strength, or safety reasons. Wood is the only one that performs in all three categories and stores carbon. Don’t be unsettled by the uncertainties portrayed about the use of wood products. The science on the subject of sustainable wood is as sure as climate change. The reality is, if you don’t grow it, you mine it!
Dave Atkins is the President of Treesource.org and a forest ecologist & forester. Sarah Larsen is a licensed architect in Oregon.