Feeding the projected 2050 world population of approximately nine billion will require global food production to be increased by some 70 per cent between now and then, but current land-based systems for food production cannot meet this extra demand. This problem is exacerbated by rising sea levels caused by climate change as land area reduction due to inundation and coastal erosion will have a major impact on the availability of agriculture land for food production.
To use less land, farms could be spread vertically rather than horizontally. This ‘Vertical Farms’ approach uses multi-layer greenhouses or skyscraper towers to intensify food production. With a controlled climate involving LED lighting and a closely monitored water/nutrient supply, these farms can produce multiple crops and high yields. But there is another option: aquaculture.
Some countries have been practicing aquaculture for many years. In the UK, salmon from fish farms is already a staple of our diet. Bren Smith, a former fisherman turned sustainable shellfish and seaweed farmer, has developed a vertical ocean farm in New York’s Long Island which uses a water column to grow a variety of species such as sugar kelp, oysters, mussels and scallops. In fact, aquaculture recently surpassed wild fishing as the primary source of protein from the ocean. However, these type of inland farms are not suitable for large-scale crop production, and so instead we may need to turn to the seas for a solution. Floating Deep Farms use large vertical shafts submerged in sea water near coastal areas. The shaft is sealed at the bottom end and is covered by a dome. A variety of crops can be grown using hydroponic planters (plant roots fed with nutrient-rich water) or aeroponics (growing plants in an air or mist environment). LED units providing illumination at appropriate wavelengths to maximise photosynthesis with minimum power input replacing sunlight. A major benefit is that crop production is largely unaffected by climatic or seasonal factors – one of the greatest limitations of conventional farming methods. Furthermore, enclosed Floating Deep Farms allow plant diseases and pests to be readily controlled with little or no application of chemical biocides.
The engineering knowhow to build marine vertical shafts is already available from the off-shore oil/gas and wind energy industries. Indeed, Floating Deep Farms could be integrated with wind turbines to power the LED lighting and other systems necessary for crop production. Such installations would not be subject to seasonal light variation, continuing with production throughout the year.
About 70 per cent of the Earth is covered with seawater. The fresh water required by the Floating Deep Farm can be created through a simple seawater evaporation desalination unit driven by a combination of solar energy and waste heat from LED lights. It is anticipated that much of the fresh water will be recycled, so, after initial charging, only a limited quantity of ‘make-up’ water will be required. The quantity of water required will be reduced by 80 per cent compared to conventional land-based agriculture.
Unlike conventional greenhouses, which rely heavily on heating and cooling systems, the submersion into seawater offers a stable temperature throughout the year. The diurnal fluctuations in solar radiation and temperature that limits the productivity of many plants will be eliminated by the farms’ closed environments.
The Floating Deep Farm can also be designed to incorporate an aquaculture for fish and other species (scallops and mussels, for example). This will allow oxygen generated by the plants to be fed directly into the fish sections of the farms. Structures would need to withstand extreme weather, but offshore wind turbine technology has already addressed these problems.
Eighteen of the word’s megacities which are located along the coastal areas could use Floating Deep Farms to supply fresh crops instead of using frozen food transported by refrigerated trailers. This will help to reduce expensive carbon miles caused by mass food importation and therefore minimise the world’s overall carbon footprint. This would address food shortage in developing and third world countries with coastal areas.
Floating Deep Farms could allow crop production all year-round. Up to ten crop cycles per year can be achieved compared to just one to two cycles for conventional agriculture. One small Deep Farm can produce around 80 tonnes of food per annum and crops can be ready for harvesting within three to four weeks of propagation. They will also have lower energy requirements than traditional vertical farms. A single Deep Farm will have about the same consumption as three UK homes using innovative LED illumination and controls combined with natural lighting using light rods or optical fibres. The carbon dioxide demand of photosynthesising plants can be captured from ambient air using materials such as activated carbon.
We have to come up with solutions such as this to address food production in countries which are vulnerable to sea level rise caused by climate change.
This was published in the April 2019 edition of Geographical magazine
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