California Air Resources Board

It is exciting to see California making the bold legislative steps needed to reduce embodied carbon in our built environment to reach net zero emission on the global scale. As there are also big moves at the state, local and national levels, coordinated action between the agencies is important, which includes looking for gaps and pooling resources to fill them. As a California native and someone who has been heavily involved in SE 2050, the Carbon Leadership Forum, and the Marin Co. Low Carbon Concrete Code development, as well as momentarily consulted on the Buy Clean CA, CalGreen embodied carbon amendments, GSA P100 requirements, and the White House Zero Emission Building definition, I am deeply interested in seeing a successful implementation AB 2446.

Two elements that are lacking in the body of new building code amendments and low carbon material procurement requirements are (1) setting maximum embodied carbon intensity (ECI) limits at the building scale and (2) collecting the data to strengthen these limits, particularly as they would need to be reduced over time and not start at the 40% reduction target on day one. Whereas initially an easily achievable limit may be set for all buildings, more data will also help to set more aggressive, yet rational, limits for different building conditions. While CalGreen contains the whole building LCA pathway, it follows the LEED approach of comparison to a hypothetical baseline and does not set a cap on the total embodied carbon. Furthermore, the material-specific GWP limits in the third pathway are higher than the industry average carbon emissions, so at this time it is unlikely many project teams will pursue the whole building reductions and most projects will not need to reduce their embodied emission at all.

CARB has an opportunity to introduce a complimentary mechanism that requires reporting at the whole building level, which can be analyzed to generate ECI benchmarks they, and CalGreen and others, can use in the future to set more rational limits on different building types and conditions. The whole building pathway offers the advantage of recognizing using less materials whereas focusing only on material-specific GWP limits does not encourage reducing material use and could even allow more total embodied carbon on project compared to a more typical design. SE 2050 and AIA 2030 have been operating databases for collection of project-level embodied carbon but do not have the remit or resources to reach the number of projects as CARB could, especially if in collaboration with CalGreen. CARB may also want to reach out to USGBC, GSA, and the White House to call for a national reporting database similar to DOE’s CBECs database of actual energy use. But action should not wait for federal support either, as City of Vancouver has demonstrated, it is possible to conduct data collection and drive embodied emissions reductions on the whole building scale at the local level.

As for the question raised on the webinar, only bottom-up (aka “process-based” in LCA terms) can differentiate between the low to high carbon intensity of a given material. Spend data is useful at a macro-scale but is not useful for the choices that project teams make that bear on embodied carbon of an individual building.

Thank you for considering my comments.