UC Davis

Limiting the rise of global mean temperatures and stabilizing Earth’s climate will require achieving net-zero emissions of long-lived greenhouse gases (GHGs) [1]. However, ongoing (residual) emissions from difficult-to-decarbonize sources, such as those from chemical reactions for commonly used products, [2,3] will need to be balanced by removal of carbon dioxide (CO2) or other GHGs from the atmosphere (hereinafter “CDR”) [4]. Enabling CDR via materials is a logical first step given the already large and growing demand for materials, eliminating the need to develop new industries for CDR. One such hard-to-carbonize material is plastic, with 99% of plastic materials made from fossil fuels. Driven by growing single-use consumer applications, the rate at which plastics are produced and disposed of is outpacing most other human-made materials. Producing plastic from bio-based feedstocks is a commonly discussed method to mitigate impacts of fossil-based plastic production and, more recently, act as a CDR mechanism. In this work, numerous pathways that could support bio-based plastics acting as a CDR strategy on a global scale by 2050 are presented. Due to their high technology-readiness and to promote a circular bioeconomy, this study focuses on the utilization of non-edible biomass resources as feedstocks for plastic production, rather than the formation of plastics from CO2 capture and utilization. Pathways are presented which consider the level of bio-based plastic market replacement, the type of energy resources used for production, as well as the prevalence of different waste management practices to systematically assess what levers need to be pulled to enable CDR in plastics. Production pathways and associated life cycle inventories for bio-based plastics from 2nd and 3rd generation feedstocks resulting in CDR are derived. To model end-of-life (EoL) impacts, a review is conducted to examine the biodegradation behavior and associated GHG emissions from bio-based plastics in different environments. Findings from this work suggest that various combinations of strategies could be employed to achieve CDR in plastics, with the greatest uptake from the scenarios considered leading to ~260 Mt of annual CDR by 2050. Considering resource availability and technological characteristics, a roadmap is generated to evaluate the feasibility of bio-based plastics acting as a CDR pathway. Building from this foundation, this research expands beyond the carbon storage potential of plastics to examine the scale of CO2 that might be stored annually in consumed construction materials and finds that fully replacing conventional building materials with CO2-storing alternatives could sequester 19.3 Gt of CO2 each year, which is roughly 50% of anthropogenic CO2 emissions emitted in 2021. This work presents a framework to analyze full lifecycle emissions of materials and determine the carbon sequestration potential utilizing a time-dependent global warming calculation. This framework allows for consistent comparisons across materials and emissions mitigation strategies at varying lifecycle stages, and it can be adapted to calculate the CDR potential for other materials with different lifespans and applications. The flexibility of this method, and the ability to identify GHG emission hot-spot lifecycle stages, will be instrumental in identifying pathways to achieve CDR through materials production.