This study examines the carbon footprints of urban agriculture (UA) compared to conventional agriculture, using a large-scale, citizen science approach across 73 UA sites in Europe and the United States. The findings reveal that the carbon footprint of food produced in UA is six times greater than that of conventional agriculture (420 gCO₂e per serving versus 70 gCO₂e per serving). However, some UA crops and sites, such as tomatoes and 25% of individually managed gardens, outperform conventional agriculture. The study identifies three key practices to reduce the carbon footprint of UA: extending the lifespan of infrastructure, using urban waste as inputs, and maximizing social benefits. These practices can help make UA more climate-friendly and sustainable. The study also highlights the importance of addressing seasonal dynamics, dietary shifts, and better data on composting techniques to refine future research and improve the environmental performance of UA.This study examines the carbon footprints of urban agriculture (UA) compared to conventional agriculture, using a large-scale, citizen science approach across 73 UA sites in Europe and the United States. The findings reveal that the carbon footprint of food produced in UA is six times greater than that of conventional agriculture (420 gCO₂e per serving versus 70 gCO₂e per serving). However, some UA crops and sites, such as tomatoes and 25% of individually managed gardens, outperform conventional agriculture. The study identifies three key practices to reduce the carbon footprint of UA: extending the lifespan of infrastructure, using urban waste as inputs, and maximizing social benefits. These practices can help make UA more climate-friendly and sustainable. The study also highlights the importance of addressing seasonal dynamics, dietary shifts, and better data on composting techniques to refine future research and improve the environmental performance of UA.