Within the context of climate change and population growth, the development of urban agriculture is of great environmental and economic significance in rapidly urbanizing China. Based on the primary survey data, this paper evaluated the carbon footprint (CF) and economic efficiency of urban agriculture in Beijing (China) using the life cycle assessment method (from cradle to consumption approach). Two cases were analyzed and compared considering their differences in on-farm cultivation and off-farm supply chains: a conventional small householder farm that sells its vegetables directly to consumers in a local market, and a large home-delivery agriculture (HDA) initiative that delivers its vegetables to the consumers’ home directly. Both cases were equipped with greenhouses with plastic covering but no heating system. The CF of the production, transportation and distribution of 1 kg fresh vegetables was estimated at 0.318 kg CO2-eq kg
۱ and 0.624e0.652 kg CO2-eq kg
۱ for conventional and HDA initiative farm, respectively. However, the HDA initiative showed a better environmental performance than the conventional operation when taking economic efficiency into consideration. The CF per unit of profit of HDA initiative (0.093e0.097 kg CO2-eq per CNY) was lower than conventional farm (0.111 kg CO2-eq per CNY). The lower CF per unit of product weight of the conventional farm was largely attributed to the high yield and the lower CF per unit of profit of the HDA initiative was mainly due to the outstanding economic profitability through income optimization. The major hotspots of CF in both cases were greenhouse plastic films in the cultivation phase (from cradle to farm gate) and transportation in the supply chain (from farm gate to consumption). Simulation of a switch to biodiesel instead of gasoline and diesel in combination with the replacement of current fossil-fuel-dominated electricity by hydro-powered electricity resulted in 20.0e21.8% reduction in the total CF. By identifying the CF hotspots of two farm cases, particular inputs and activities can be targeted for adjustment in order to effectively reduce the CF of urban agriculture in Beijing.

Introduction

As one of the major pillars of sustainable development, greenhouse gas abatement is an enormous challenge facing the rapidly urbanizing world (UNEP, 2017). Urban agriculture (UA) is an important part of the sustainable and resilient global food system, as well as one of the feasible choices to produce sufficient various food for a growing population continuously agglomerated in cities (FAO, 2014; Maxwell, 2003). However, there is an ongoing controversy about the extent to which UA can reduce carbon emission. Many researchers demonstrate that UA has lower embodied greenhouse gas emission compared with conventional supply chains (Goldstein et al., 2016a) mainly due to the shorter distance from farm to fork (Ohyama et al., 2008) and the accompanied smaller amount of waste in the post farm stage (Kulak et al., 2013; Sanye-Mengual et al., 2013 ). While some studies get contradictory results that UA could lead to an increase in carbon emission because growing some specific plants locally may require additional energy and fertilizer inputs in cultivation than imported product (Goldstein et al., 2016b; Mok et al., 2014). Therefore, the environmental impact of UA should be assessed from a whole life cycle perspective with clearly stated context and constraints.