Editing IPCC:AR6/WGIII/Chapter-12 (section)

==== 12.4.3.1 Controlled-environment Agriculture ====

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Controlled-environment agriculture is mainly based on hydroponic or aquaponic cultivation systems that do not require soil. Aquaponics combine hydroponics with a re-circulating aquaculture compartment for integrated production of plants and fish ( [[#Junge--2017|Junge et al. 2017]] ; [[#Maucieri--2018|Maucieri et al. 2018]] ), while aeroponics is a further development of hydroponics that replaces water as a growing medium with a mist of nutrient solution ( [[#Al-Kodmany--2018|Al-Kodmany 2018]] ). Aquaponics could potentially produce proteins in urban farms, but the technology is not yet mature and its economic and environmental performance is unclear ( [[#Love--2015|Love et al. 2015]] ; [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ).

Controlled-environment agriculture is often undertaken in urban environments to take advantage of short supply chains ( [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ), and might use abandoned buildings or be integrated in supermarkets, producing for example herbs ‘on demand’.

Optimising growing conditions, hydroponic systems achieve higher yields than un-conditioned agriculture ( [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ); and yields can be further enhanced in CO 2 -enriched atmospheres ( [[#Shamshiri--2018|Shamshiri et al. 2018]] ; [[#Armanda--2019|Armanda et al. 2019]] ). By using existing spaces or modular systems that can be vertically stacked, this technology minimises land demand, however it is energy intensive and requires large financial investments. So far, only a few crops are commercially produced in vertical farms, including lettuce and other leafy greens, herbs and some vegetables, due to their short growth period and high value ( [[#Benke--2017|Benke and Tomkins 2017]] ; [[#Armanda--2019|Armanda et al. 2019]] ; [[#Beacham--2019|Beacham et al. 2019]] ; [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ). Through breeding, other crops could reach commercial feasibility, or crops with improved taste or nutritional characteristics can be grown ( [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ).

In controlled-environment agriculture, photosynthesis is fuelled by artificial light through LEDs or a combination of natural light with LEDs. Control of the wave band and light cycle of the LEDs and micro-climate can be used to optimise photosynthetic activity, yield and crop quality ( [[#Gómez--2018|Gómez and Gennaro Izzo 2018]] ; [[#Shamshiri--2018|Shamshiri et al. 2018]] ).

Co-benefits of controlled-environment agriculture include minimising water and nutrient losses as well as agro-chemical use ( [[#Al-Kodmany--2018|Al-Kodmany 2018]] ; [[#Shamshiri--2018|Shamshiri et al. 2018]] ; [[#Armanda--2019|Armanda et al. 2019]] ; [[#Farfan--2019|Farfan et al. 2019]] ; [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ; [[#Rufí-Salís--2020|Rufí-Salís et al. 2020]] ) ( ''robust evidence, high agreement'' ). Water is recycled in a closed system and additionally some plants generate fresh water by evaporation from grey or black water, and high nutrient use efficiencies are possible. Food production from controlled-environment agriculture is independent of weather conditions and able to satisfy some consumer demand for locally-produced fresh and diverse produce throughout the year ( [[#Benke--2017|Benke and Tomkins 2017]] ; [[#Al-Kodmany--2018|Al-Kodmany 2018]] ; [[#O’Sullivan--2019|O’Sullivan et al. 2019]] ).

Controlled-environment agriculture is a very energy intensive technology (mainly for cooling) and its GHG intensity depends therefore crucially on the source of the energy. Options for reducing GHG intensity include reducing energy use through improved lighting and cooling efficiency or by employing low-carbon energy sources, potentially integrated into the building structure ( [[#Benke--2017|Benke and Tomkins 2017]] ).

Comprehensive studies assessing the GHG balance of controlled-environment agriculture are lacking. The overall GHG emissions from controlled-environment agriculture is therefore uncertain and depends on the balance of reduced GHG emissions from production and distribution and reduced land requirements, versus increased external energy needs.

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