Greenhouses require large amounts of energy, which is the dominant factor making greenhouses more emission intensive than open-field cultivation. Alternative heating systems, such as combined heat and power (CHP), biogas, and industrial waste heat, are continuously being researched for reducing the environmental impacts of greenhouses. This paper assesses utilizing industrial waste heat and CO2 enrichment in greenhouses as an example to propose “agro-industrial symbiosis” (AIS), to refer to a symbiotic co-operation between agricultural and industrial partners. The global warming potentials (GWPs) of greenhouse production using different heating systems are inadequately compared in the literature, which is the research gap addressed herein. Additionally, potential emission reductions of greenhouse production with industrial waste heat are yet to be assessed via lifecycle assessment (LCA). A comparative LCA of Finnish greenhouse tomato and cucumber production using various heating systems was conducted. Naturally, replacing fossil fuels with bioenergy and renewables significantly decreases the GWP. CHP systems result in decreased GWP only when using biogas as the energy source. Additionally, utilizing industrial waste heat and CO2 resulted in a low GWP. These results are applicable worldwide to guide political decision-making and clean energy production in the horticultural sector.