Is ‘local food’ best? Evaluating agricultural greenhouses in Switzerland as an alternative to imports for reducing carbon footprint

Abstract

Sustainable agricultural practices are essential to mitigate environmental impacts. Greenhouse cultivation offers potential solutions for enhancing crop yields and reducing the impacts on land and water resources. However, reliance on fossil-based heating systems poses challenges regarding carbon footprint. This study provides a comparative life cycle assessment (LCA) of the carbon and water footprints of imported and locally produced greenhouse crops in Switzerland, considering the local climatic conditions and the predominant production systems in different regions. The findings reveal that the carbon footprint is primarily driven by heating, supplementary lighting, and CO₂ fertilization, while transportation emissions are relatively minor. A key insight is that using waste heat for greenhouse heating in Switzerland can reduce the carbon footprint to less than one-third (e.g., 0.6 CO₂-eq/kg for tomatoes) compared to local natural-gas-based heating systems. However, imports from warmer locations still show a slightly lower carbon footprint (0.4-0.5 CO₂-eq/kg) due to the absence of heating, lighting, and CO₂ enrichment, but often come with trade-offs concerning the water footprint. Seasonal variations also strongly influence the carbon footprint: early winter cultivation can result in up to five times higher carbon footprint than summer cultivation, while waste-heat systems reduce but do not eliminate this effect. These findings highlight the potential of waste-heat-based greenhouses as a lower-carbon alternative to fossil-fueled domestic production and imports from less favorable climates while underscoring the environmental benefits of seasonal diets.