Please help me understand why the 2021 Material Baseline Report shows a high GWP for composite lumber (400 kg CO2e) and mass timber (200 kg CO2e). When I think of wood, I would think the GWP would be a negative number or a carbon sink, right?
See page 10 of the report.
Link to Report: 2021 Material Baseline Report - Carbon Leadership Forum
(first time posting on this site. apologies in advance if this is the wrong location or if this question has already been answered)
I am unsure how standards set out EPDs in North America but within Europe, they have to report sequestered carbon separately from fossil carbon, which can then be aggregated into a global warming potential total. Within a life cycle assessment, if you are only reporting A1-A5 then the sequestered carbon needs to be reported separately from the fossil carbon. For the baseline report, it states that only A1-A3 are declared however, I am unsure why the sequestered carbon is not also reported separately.
You can calculate the sequestered carbon yourself as it is defined that half the dry mass of any timber is carbon, which can then be given an equivalent CO2 value. For example, if the timber has a density of 400kg/m3 with 12% moisture content then the dry mass will be 357kg/m3. The biogenic/sequestered carbon is 357 * 0.5 = 178.5kg carbon. Therefore, the sequestered CO2e is 178.5 * 44/12 = 665 kgCO2e/m3.
Hope this helps!
To add that there is lot of adhasives and glues on the composte lumber that pushes the emissions up quite a lot. If you want to check out and compare more options do sign up to One Click LCA Free Trial. You can find 1000’s of datapoints to check out (https://www.oneclicklca.com/).
@Kevin_Conklin - more discussion on biogenic carbon in this thread. Also a very interesting and insightful presentation by @anthony.pak here.
Thank you for the responses! I’ve learned a lot and still have a long way to go.