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Vertical farming is the practice of growing crops in vertically stacked layers. It often incorporates controlled-environment agriculture, which aims to optimize plant growth, and soilless farming techniques such as hydroponics, aquaponics, and aeroponics. Some common choices of structures to house vertical farming systems include buildings, shipping containers, underground tunnels, and abandoned mine shafts.

The modern concept of vertical farming was proposed in 1999 by Dickson Despommier, professor of Public and Environmental Health at Columbia University. Despommier and his students came up with a design of a skyscraper farm that could feed 50,000 people. Although the design has not yet been built, it successfully popularized the idea of vertical farming. Current applications of vertical farmings coupled with other state-of-the-art technologies, such as specialized LED lights, have resulted in over 10 times the crop yield than would receive through traditional farming methods. There have been several different means of implementing vertical farming systems into communities such as: Paignton, Israel , Singapore , Chicago , Munich , London , Japan , and Lincolnshire.

The main advantage of utilizing vertical farming technologies is the increased crop yield that comes with a smaller unit area of land requirement. The increased ability to cultivate a larger variety of crops at once because crops do not share the same plots of land while growing is another sought-after advantage. Additionally, crops are resistant to weather disruptions because of their placement indoors, meaning less crops lost to extreme or unexpected weather occurrences. Lastly, because of its limited land usage, vertical farming is less disruptive to the native plants and animals, leading to further conservation of the local flora and fauna.

Vertical farming technologies face economic challenges with large start-up costs compared to traditional farms. In Victoria, Australia, a “hypothetical 10 level vertical farm” would cost over 850 times more per cubic meter of arable land than a traditional farm in rural Victoria. Vertical farms also face large energy demands due to the use of supplementary light like LEDs. Moreover, if non-renewable energy is used to meet these energy demands, vertical farms could produce more pollution than traditional farms or greenhouses.

Hydroponics
Hydroponics refers to the technique of growing plants without soil. In hydroponic systems, the roots of plants are submerged in liquid solutions containing macronutrients, such as nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium, as well as trace elements, including iron, chlorine, manganese, boron, zinc, copper, and molybdenum. Additionally, inert (chemically inactive) mediums such as gravel, sand, and sawdust are used as soil substitutes to provide support for the roots.

The advantages of hydroponics include the ability to increase yield per area and reduce water usage. A study has shown that, compared to conventional farming, hydroponic farming could increase the yield per area of lettuce by around 11 times while requiring 13 times less water. Due to these advantages, hydroponics is the predominant growing system used in vertical farming.

Aquaponics
The term aquaponics is coined by combining two words: aquaculture, which refers to fish farming, and hydroponics -- the technique of growing plants without soil. Aquaponics takes hydroponics one step further by integrating the production of terrestrial plants with the production of aquatic organisms in a closed-loop system that mimics nature itself. Nutrient-rich wastewater from the fish tanks is filtered by a solid removal unit and then led to a bio-filter, where toxic ammonia is converted to nutritious nitrate. While absorbing nutrients, the plants then purify the wastewater, which is recycled back to the fish tanks. Moreover, the plants consume carbon dioxide produced by the fish, and water in the fish tanks obtains heat and helps the greenhouse maintain temperature at night to save energy. As most commercial vertical farming systems focus on producing a few fast-growing vegetable crops, aquaponics, which also includes an aquacultural component, is currently not as widely used as conventional hydroponics.

Aeroponics
The invention of aeroponics was motivated by the initiative of NASA (the National Aeronautical and Space Administration) to find an efficient way to grow plants in space in the 1990s. Unlike conventional hydroponics and aquaponics, aeroponics does not require any liquid or solid medium to grow plants in. Instead, a liquid solution with nutrients is misted in air chambers where the plants are suspended. By far, aeroponics is the most sustainable soilless growing techniques, as it uses up to 90% less water than the most efficient conventional hydroponic systems and requires no replacement of growing medium. Moreover, the absence of growing medium allows aeroponic systems to adopt a vertical design, which further saves energy as gravity automatically drains away excess liquid, whereas conventional horizontal hydroponic systems often require water pumps for controlling excess solution. Currently, aeroponic systems have not been widely applied to vertical farming, but are starting to attract significant attention.

Controlled-environment Agriculture
Controlled-environment agriculture (CEA) is the modification of the natural environment to increase crop yield or extend the growing season. CEA systems are typically hosted in enclosed structures such as greenhouses or buildings, where control can be imposed on environmental factors including air, temperature, light, water, humidity, carbon dioxide, and plant nutrition. In vertical farming systems, CEA is often used in conjunction with soilless farming techniques such as hydroponics, aquaponics, and aeroponics.

Building-based vertical farms
Abandoned buildings are often reused for vertical farming, such as a farm at Chicago called “The Plant,” which was transformed from an old meatpacking plant. However, new builds are sometimes also constructed to house vertical farming systems. For example, a company named "Vertical Harvest" built a three-story hydroponic greenhouse next to a parking lot in Jackson, Wyoming, and aims to grow 100,000 lbs of produce annually.

Shipping-container vertical farms
Recycled shipping containers are an increasingly popular option for housing vertical farming systems. The shipping containers serve as standardized, modular chambers for growing a variety of plants, and are often equipped with LED lighting, vertically stacked hydroponics, smart climate controls, and monitoring systems. Moreover, by stacking the shipping containers, farms can save space even further and achieve higher yield per square foot. Currently, there are many commercial shipping-container vertical-farming units on the market, such as the “Greenery” from Freight Farms and the “TerraFarm” from Local Roots.

Deep farms
A “deep farm” is a vertical farm built from refurbished underground tunnels or abandoned mine shafts. As temperature and humidity underground are generally temperate and constant, deep farms require less energy for heating. Deep farms can also use nearby groundwater to reduce the cost of water supply. Despite low costs, a deep farm can produce 7 to 9 times more food than a conventional farm above ground on the same area of land, according to Saffa Riffat, chair in Sustainable Energy at the University of Nottingham. Coupled with automated harvesting systems, these underground farms can be fully self-sufficient.

A company named “Growing Underground” claims to have built the world’s first underground farm, and is growing greens in a refurbished World War II bomb shelter 33 meters under Clapham, London. Their products are available in local supermarkets such as Whole Foods, Planet Organic, and M&S.

Proposal of vertical farming [added by Joyce]
Dickson Despommier, professor of Public and Environmental Health at Columbia University, founded the root of the concept of vertical farming. In 1999, he challenged his class of graduate students to calculate how much food they could grow on the rooftops of New York. The student concluded that they could only feed about 1000 people. Unsatisfied with the results, Despommier suggested growing plants indoors instead, on multiple layers vertically. Despommier and his students then proposed a design of a 30-story vertical farm equipped with artificial lighting, advanced hydroponics, and aeroponics that could produce enough food for 50,000 people. They further outlined that approximately 100 kinds of fruits and vegetables would grow on the upper floors while lower floors would house chickens and fish subsisting on the plant waste. Although Despommier’s skyscraper farm has not yet been built, it popularized the idea of vertical farming and inspired many later designs. === Implementations of vertical farming [to be revised by Eric] === Developers and local governments in multiple cities have expressed interest in establishing a vertical farm: Incheon (South Korea), Abu Dhabi (United Arab Emirates), Dongtan (China), New York City, Portland, Los Angeles, Las Vegas , Seattle, Surrey, Toronto, Paris, Bangalore, Dubai, Shanghai, and Beijing.

In 2009, the world's first pilot production system was installed at Paignton Zoo Environmental Park in the United Kingdom. The project showcased vertical farming and provided a sollid base to research sustainable urban food production. The produce is used to feed the zoo's animals while the project enables evaluation of the systems and provides an educational resource to advocate for change in unsustainable land-use practices that impact upon global biodiversity and ecosystem services.

In 2010 the Green Zionist Alliance proposed a resolution at the 36th World Zionist Congress calling on Keren Kayemet L'Yisrael (Jewish National Fund in Israel) to develop vertical farms in Israel. Moreover, a company named "Podponics" built a vertical farm in Atlanta consisting of over 100 stacked "growpods" in 2010 but reportedly went bankrupt in May 2016.

In 2012 the world's first commercial vertical farm was opened in Singapore, developed by Sky Greens Farms, and is three stories high. They currently have over 100 nine meter-tall towers.

In 2012, a company named The Plant debuted its newly-developed vertical farming system housed in an abandoned meatpacking building in Chicago, Illinois. The utilization of abandoned buildings to house vertical farms and other sustainable farming methods are a fact of the rapid urbanization of modern communities.

In 2013 the Association for Vertical Farming (AVF) was founded in Munich (Germany). By May 2015, the AVF had expanded with regional chapters all over Europe, Asia, USA, Canada and the United Kingdom. This organization unites growers and inventors to improve food security and sustainable development. The AVF focuses on advancing vertical farming technologies, designs and businesses by hosting international info-days, workshops, and summits.

In 2015 the London company, Growing Underground, began the production of leafy green produce underground in abandoned underground World War II tunnels.

In 2016, a startup called Local Roots launched the "TerraFarm", a vertical farming systems hosted in a 40-foot shipping container, which includes computer vision integrated with an artificial neural network to monitor the plants; and is remotely monitored from California. It is claimed that the TerraFarm system "has achieved cost parity with traditional, outdoor farming" with each unit producing the equivalent of "three to five acres of farmland," using 97% less water through water recapture and harvesting the evaporated water through the air conditioning.

In 2017, a Japanesse company, Mirai, began marketing its multi-level vertical farming system with impressive statistics. The company states that can produce 10,000 heads of lettuce a day - 100 times the amount that could be produced with traditional agricultural methods, because their special purpose LED lights can decrease growing times by a factor of 2.5. Additionally, this can all be achieved with 40% less energy usage, 80% less food waste, and 99% less water usage than in traditional farming methods. Further requests have been made to implement this technology in several other Asian countries.

In 2018, plans were developed for the largest indoor farm in Europe. The Lincolnshire-based, Jones Food Company farm is rumored to produce 420 tonnes of leafy greens per year while utilizing the amount of area of 26 tennis courts. All of this is achieved while using 90 percent less water and 50 percent less pesticides.

In 2019, Freight Farms announced the "Greenery," a complete farm-to-table system outfitted with vertical hydroponics, LED lighting, and intuitive climate controls built within a 12 m × 2.4 m shipping container.

== Advantages [existing] [to be revised] ==



Agricultural Efficiency
Traditional farming’s arable land requirements are too large and invasive to remain sustainable for future generations. With the ever-so-rapid population growth rates, it is expected that arable land per person will drop about 66% in 2050 in comparison to 1970. Vertical farming allows for, in some cases, over ten times the crop yield per acre than traditional methods. Unlike traditional farming in non-tropical areas, indoor farming can produce crops year-round. All-season farming multiplies the productivity of the farmed surface by a factor of 4 to 6 depending on the crop. With crops such as strawberries, the factor may be as high as 30.

Vertical farming also allows for the production of a larger variety of harvestable crops because of its usage of isolated crop sectors. As opposed to a traditional farm where one type of crop is harvested per season, vertical farms allow for a multitude of different crops to be grown and harvested at once due to their individual land plots.

Resistance to Weather
Crops grown in traditional outdoor farming depend on supportive weather, and suffer from undesirable temperatures rain, monsoon, hailstorm, tornado, flooding, wildfires and drought. "Three recent floods (in 1993, 2007 and 2008) cost the United States billions of dollars in lost crops, with even more devastating losses in topsoil. Changes in rain patterns and temperature could diminish India's agricultural output by 30 percent by the end of the century."

The issue of adverse weather conditions is especially relevant for arctic and sub-arctic areas like Alaska and northern Canada where traditional farming is largely impossible. Food insecurity has been a long-standing problem in remote northern communities where fresh produce has to be shipped large distances resulting in high costs and poor nutrition. Container-based farms can provide fresh produce year-round at a lower cost than shipping in supplies from more southerly locations with a number of farms operating in locations such as Churchill, Manitoba and Unalaska, Alaska. As with disruption to crop growing, local container-based farms are also less susceptible to disruption than the long supply chains necessary to deliver traditionally grown produce to remote communities. Food prices in Churchill spiked substantially after floods in May and June 2017 forced the closure of the rail line that forms the only permanent overland connection between Churchill and the rest of Canada.

Environmental Conservation
Up to 20 units of outdoor farmland per unit of VF could return to its natural state, due to VF's increased productivity. Vertical farming would reduce the amount of farmland, thus saving many natural resources.

Deforestation and desertification caused by agricultural encroachment on natural biomes could be avoided. Producing food indoors reduces or eliminates conventional plowing, planting, and harvesting by farm machinery, protecting soil and reducing emissions.

Traditional farming is often invasive to the native flora and fauna because it requires such a large area of arable land. One study showed that wood mouse populations dropped from 25 per hectare to 5 per hectare after harvest, estimating 10 animals killed per hectare each year with conventional farming. In comparison, vertical farming would cause nominal harm to wildlife because its limited space usage.

Economics
Vertical farms must overcome the financial challenge of large startup costs. ''The initial building costs would exceed $100 million, for a 60 hectare vertical farm. Office occupancy costs can be high in major cities, with office space in cities such as Tokyo, Moscow, Mumbai, Dubai, Milan, Zurich, and Sao Paulo ranging from $1850 to $880 per square meter.[citation 41 from the original wikipedia article]'' Since vertical farms are meant to be located in the centers of major cities, owners of vertical farms would have to pay the occupancy costs that any other office in the same zone would have to pay. In Victoria, Australia a hypothetical 10-level vertical farm would have a cost of US$349 per square meter of arable land, whereas a traditional farm in rural Victoria would have a cost of US$0.40 per square meter of arable land. Eventually as vertical farms become more efficient, the startup cost will be overcome, however even a vertical farm with a yield per hectare factor 50 times larger than a traditional farm’s yield, it would take 6-7 years for the vertical farm to break even in costs.

Opponents question the potential profitability of vertical farming. In order for vertical farms to be successful financially, high value cops must be grown since traditional farms provide low value crops like wheat at cheaper costs than a vertical farm. Louis Albright, a professor in biological and environmental engineering at Cornell stated that a loaf of bread that was made from wheat grown in a vertical farm would cost US$27. However, according to the US Bureau of Labor Statistics, the average loaf of bread cost US$1.296 in September of 2019, clearly showing how crops grown in vertical farms will be noncompetitive compared to crops grown in traditional outdoor farms. In order for vertical farms to be profitable, the costs of operating these farms must decrease.

''The developers of the TerraFarm system produced from second hand, 40 foot shipping containers claimed that their system "has achieved cost parity with traditional, outdoor farming". ''

Energy use
'''[same intro sentence]During the growing season, the sun shines on a vertical surface at an extreme angle such that much less light is available to crops than when they are planted on flat land. Therefore, supplemental light would be required. Bruce Bugbee claimed that the power demands of vertical farming would be noncompetitive with traditional farms using only natural light[]'''. Environmental writer George Monbiot calculated that the cost of providing enough supplementary light to grow the grain for a single loaf would be about $15. An article in the Economist argued that "even though crops growing in a glass skyscraper will get some natural sunlight during the day, it won't be enough" and "the cost of powering artificial lights will make indoor farming prohibitively expensive". Moreover, researchers determined that if only solar panels were to be used to meet the energy consumption of a vertical farm, “the area of solar panels required would need to be a factor of twenty times greater than the arable area on a multi-level indoor farm”, which will be hard to accomplish with larger vertical farms. A hydroponic farm growing lettuce in Arizona would require 15,000 kJ of energy per kilogram of lettuce produced. To put this amount of energy into perspective, a traditional outdoor lettuce farm in Arizona only requires 1100 kJ of energy per kilogram of lettuce grown.

As "The Vertical Farm" proposes a controlled environment, heating and cooling costs will resemble those of any other tower. Plumbing and elevator systems are necessary to distribute nutrients and water. In the northern continental United States, fossil fuel heating cost can be over $200,000 per hectare. Research conducted in 2015 compared the growth of lettuce in Arizona using conventional agricultural methods and a hydroponic farm. They determined that heating and cooling made up more than 80% of the energy consumption in the hydroponic farm, with the heating and cooling needing 7400 kJ per kilogram of lettuce produced. According to the same study, the total energy consumption of the hydroponic farm is 90,000 kJ per kilogram of lettuce. If the energy consumption is not addressed, vertical farms may be an unsustainable alternative to traditional agriculture.

Pollution
If power needs are met by fossil fuels, the environmental effect may be a net loss ; even building low-carbon capacity to power the farms may not make as much sense as simply leaving traditional farms in place, while burning less coal. Louis Albright argued that in a “closed-system urban farming based on electrically generated photosynthetic light”, a pound of lettuce would result in 8 pounds of carbon dioxide being produced at a power plant, and 4,000 pounds of lettuce produced would be equivalent to the annual emissions of a family car. He also argues that the carbon footprint of tomatoes grown in a similar system would be twice as big as the carbon footprint of lettuce. However, lettuce produced in a greenhouse that allows for sunlight to reach the crops saw a 300 percent reduction in carbon dioxide emissions per head of lettuce. As vertical farm system become more efficient in harnessing sunlight, the less pollution they will produce.

[the next 3 paragraphs stayed the same as the original]Greenhouses commonly supplement CO2 levels to 3–4 times the atmospheric rate. This increase in CO2 increases photosynthesis rates by 50%, contributing to higher yields. Some greenhouses burn fossil fuels purely for this purpose, as other CO2 sources, such as those from furnaces, contain pollutants such as sulphur dioxide and ethylene which significantly damage plants. This means a vertical farm requires a CO2 source, most likely from combustion. Also, necessary ventilation may allow CO2 to leak into the atmosphere.

Greenhouse growers commonly exploit photoperiodism in plants to control whether the plants are in a vegetative or reproductive stage. As part of this control, the lights stay on past sunset and before sunrise or periodically throughout the night. Single story greenhouses have attracted criticism over light pollution.

Hydroponic greenhouses regularly change the water, producing water containing fertilizers and pesticides that must be disposed of. The most common method of spreading the effluent over neighbouring farmland or wetlands would be more difficult for an urban vertical farm. 10/28/19 HC Comments: consider adding a section for working farms or VF farming efforts around the world