Organic and Conventional Dairy Farming in Europe: A Cross-Study Systematic Review of Life Cycle Assessment Outcomes

Environmental impacts vary largely among different dairy production systems, and there is a lack of consensus on the sustainability of organic systems compared to conventional dairy systems internationally. This study aims to compare the two dairy systems to determine whether there is a difference in environmental sustainability and to synthesize life cycle assessment (LCA) findings in the context of Europe’s sustainability targets. A search was conducted using various databases and search terms, based on established criteria, to identify LCA studies comparing organic and conventional dairy farming in Europe. Information on LCA impact categories (global warming potential, GWP; acidification potential, AP; eutrophication potential, EP; land use, LU and energy use, EU) in addition to non-LCA parameters was retrieved. Methodological differences in LCA studies prevent direct comparisons; therefore, response ratios (Rr) were used to compare the different indicators, with a one-sample t -test assessing significance. Data from 18 papers from 10 European countries were analyzed. Farm characteristics showed that organic systems had significantly ( p < 0.05) lower milk yield, stocking rate, concentrate input, diesel, and pesticide use compared to conventional systems. The results showed a non-significant lower mean Rrs for the GWP, AP, and EP impacts of the organic systems relative to the conventional system per unit product. Organic systems showed lower energy requirements (Rr = −0.29, p < 0.05), with a higher land use percentage (41%, p < 0.05) per unit product. When impacts were related to one hectare of occupied area, all impact categories (GWP, AP, EP, and EU) were significantly lower ( p < 0.05) in organic systems. It remains challenging to draw conclusions about the best sustainable dairy management systems when both productivity and environmental impacts are considered. Land-based functional units focus on extensive, low-impact land-farming systems while largely overlooking productivity, thereby often indicating more favourable environmental performance than product-based metrics. Overall, this study highlights substantial differences in farm management practices between organic and conventional systems and demonstrates that variability in LCA methodological choices is a key driver shaping the magnitude and robustness of comparative environmental results.