What can we learn about the climate change impacts of polylactic acid from a review and meta-analysis of lifecycle assessment studies?

Frequently cited advantages of bio-based polymers include a lower carbon footprint compared to fossil-based polymers and biodegradation to avoid microplastic pollution. These expectations also apply to polylactic acid (PLA), one of the most advanced bio-based polymers on the market. Over 80 life cycle assessments and carbon footprinting studies of PLA have been performed since the early 2000s. In this review and meta-analysis, the results for global warming potential (GWP) and acidification potential from these studies were compared to clarify whether an overall conclusion can be made about the advantages of PLA over fossil-based polymers. When looking at cradle-to-gate: resin scope, the median GWP value for PLA was 1.63 kg CO₂ eq/kg PLA, which is lower than that of fossil polymers such as polyethylene terephthalate (PET), polypropylene (PP), or polyethylene (PE). However, the median value of PLA from cradle-to-grave studies was 3.91 kg CO₂ eq/kg, comparable to the GWP of fossil polymers. This discrepancy is primarily a result of biogenic carbon accounting, where the cradle-to-gate results benefit from CO₂ uptake by feedstock. Significant variation was observed in the GWP for PLA between the different studies, stemming from different choices made by the authors concerning the type of feedstock, electricity mix, end-of-life option, or aforementioned biogenic carbon accounting.