Unravelling life cycle impacts of coffee: Why do results differ so much among studies?

Coffee beans are a major agricultural product and coffee is one of the most widely traded commodities and consumed beverages globally. Supply chains and cropping systems are very diverse, with contrasted potentials and performance, as well as environmental impacts. Life Cycle Assessment (LCA) studies are needed to inform on reduction in impacts, but there is a lack of comprehensive understanding of the variability of existing LCA results and impacts of the cropping systems and their trade-offs along the supply chains. In an attempt to address this knowledge gap, the paper presents a systematic literature review of coffee LCA, considering a total of 34 studies covering 234 coffee systems. Global warming potential (GWP) was the impact category most reported in the literature, but the results varied greatly at both the farm and drink levels. For the former, the GWP values ranged from 0.15 to 14.5 (median: 3.6) kg CO2 eq./kg green coffee beans and for the latter the values ranged from 2 to 23 (median: 8.8) kg CO2 eq./kg consumed coffee in drinks. Main contributors to the GWP of production of green coffee beans were land use change (LUC), fertilisers and wet processing. However, there were great inconsistencies across studies in terms of LUC accounting, field emissions and wet process modelling. Green coffee beans production was also the main contributor to the GWP of coffee consumed, followed by brewing and coffee cup washing. Some studies covered other impacts, in addition to GWP. At both the farm and drink levels, fertilisers and pesticides were the main contributors to eutrophication and acidification, and to ecotoxicity, respectively. Brewing was the second main contributor at the drink level, in some cases the top contributor for energy-related indicators. Assumptions on packaging, cup washing and waste disposal were highly variable across studies. Water impact indicators were hardly comparable due to the system variability and method inconsistencies. Given the large diversity of coffee cropping systems worldwide, but also the diversity of possible coffee drinks, we recommend that LCA studies be standardised with respect to the definition of the functional unit, including consistent quality aspects for both green coffee beans (moisture) and coffee drinks (organoleptic properties). They should also be more thorough in detailing processes at all stages. More attention should be paid to the farming system complexity and a mass balance should be ensured when assessing biomass flows concerning LUC, co-products and residue emissions. Finally, more primary data would be needed to decipher the cropping system diversity, as well as to characterise emissions from all inputs to the field and bean processing, notably for wet and semi-wet processing.