Apples to Apples: Are Vertical Farms Better for the Environment?
A few weeks ago, I had an opportunity to visit Plenty in South San Francisco. Their vertical farm is an impressive display of one vision for the future of agriculture: a fully-automated system that grows produce in a space-efficient controlled environment. Wearing goggles to protect our eyes from the harsh red and blue LED light, our stroll through the indoor farm felt like a sharp departure from the small family farm where I spent my childhood. Vertical farming companies like Plenty are currently at the center of an environmental debate: is vertical farming better for the environment than growing produce in the field? Many smart, informed people have made compelling arguments for both sides of this debate. My goal for this article is lay out some of the issues and form an opinion on the future of vertical farming.
Proponents of Vertical Farming:
- CO2 Emissions Scoping; Comparison Between Different Farming Methods in Lettuce Production. One Farm, 2018.
- Yes, Indoor Agriculture Can Feed the World. Micki Seibel of Radical Growth, 2018.
- Don’t Count Out Vertical Farms. Dan Blaustein-Rejto of The Breakthrough Institute, 2018.
Critics of Vertical Farming:
- No, Vertical Farms Won’t Feed the World. Dr. Jonathan Foley of Project Drawdown, 2018.
- Enough with the vertical farming fantasies: There are still too many unanswered questions about the trendy practice. Stan Cox of The Land Institute, 2016.
- The buzz around indoor farms and artificial lighting makes no sense. Michael Hamm of Michigan State University, 2015.
Definition of a Vertical Farm (and other forms of Controlled Environment Agriculture)
Before I start, it’s important to define what we mean by “vertical farming.” Vertical farms are a type of Controlled Environment Agriculture (CEA), a broad category that also includes high tunnels and greenhouses. All of these indoor farms impose some form of control over the growing environment.
High tunnels, being the simplest type of CEA, only use a plastic structure to trap heat from the sun within an enclosed space (this is the origin of the term “greenhouse effect”). High tunnels are used to extend the growing season into colder months, allowing the farm to grow more food throughout the year.
Greenhouses, of course, also make use of the greenhouse effect to trap heat, and tend to be slightly more advanced than high tunnels. Greenhouses may make use of hydroponics, aquaponics, or aeroponics to recycle water and deliver nutrients to the plants. Greenhouses may also make use of supplementary heat sources to better control the temperature.
Vertical farms are a whole different level of controlled environment agriculture. Vertical farms replace the sun with LED lighting, which helps to maximize yield per acre by (1) stacking plants on top of each other and (2) giving the plants the optimal amount of light 24 hours per day. This level of environmental control comes at a steep energy cost, which is the center of this environmental debate.
Claims and Critiques of Vertical Farms
Proponents make a number of different claims that support the environmental benefits of vertical farms.
Claims of Vertical Farms
- More Productive: Vertical farms can grow more produce per acre (10x, 100x, 157x). By reducing the amount of land needed to grow food, farmland can be returned to natural habitat.
- More Local: Vertical farms can grow produce closer to the point of consumption. This reduces the distance that food needs to travel (i.e. food miles), saving as much as 95% of shipping fuel.
- Less Waste: The NRDC reports that as much as 40% of food is wasted along the value chain. ReFED reports that 16% of this waste occurs at the farm, likely due to damage or the produce not meeting commercial market requirements. Nearly all produce grown in the controlled environment of a vertical farm is harvested, and it spends fewer days traveling to the point of consumption.
- Less Water: By recycling water through the hydroponic or aeroponic system, vertical farms can use as little as 5% of the water used by field agriculture.
- More Reliable: Vertical farms offer a more reliable source of produce because they are not dependent on the weather. At the time of writing, the U.S. is facing an arugula shortage due to cold, wet weather.
- Healthier, Safer, and Tastier: A shorter supply chain means less chance of contamination and more nutritional food.
The critics are quick to counter many of these points:
Critiques of Vertical Farms
- Energy Use: Field agriculture uses a free resource: the sun. The LEDs in vertical farms can be powered by solar panels, but this means capturing sunlight to then recreate the sun, all at a loss in efficiency. Freight Farm units require 150–165 kWh per day to power the lights, heating, and ventilation. This is roughly equivalent to the annual energy consumption of five U.S. households. (LEDs, however, are projected to double in efficiency by 2030 and Plenty reported cutting energy consumption by 80% per kilogram of plants grown in 2018.)
- Low Emission Crops: Agricultural activities generate roughly one third of human greenhouse gas emissions, but the majority of this is caused by meat and dairy production and not lettuce and tomatoes. Vertical farms are an investment in the wrong problem (see chart below).
- Food Miles Aren’t a Big Problem: Apart from the produce that requires air freight, transporting food isn’t a big climate problem and represents only 11% of the lifecycle greenhouse gas emissions.
- Land Required for Renewable Energy: It’s estimated that 3.4 sq. ft. of solar panels are required for each sq. ft. of growing area. (Proponents would counter and say that net land use is still significantly less, due to productivity per sq. ft. — see claim #1 above.)
Back to the Question — Are Vertical Farms Better for the Environment?
To properly answer this question, one would need to do a full lifecycle analysis of a vertical farm and its impact on the downstream supply chain. There have been several attempts to do this:
- Martin & Molin suggest vertical farms are capable of growing produce at a carbon footprint of 0.27–0.74 kg CO2-eq per kg of edible plant material.
- Romeo et al. suggests that vertical farms have a carbon footprint of approximately 0.39 kg CO2-eq per kg of lettuce grown. This rate assumes the farm is powered by the French energy mix, which is 70% nuclear. When this energy source is replaced entirely with wind power, the environmental impact is reduced to 0.156 kg CO2-eq per kg of lettuce grown.
- Eero Hallikainen’s analysis, however, suggests a minimum carbon footprint of approximately 4.0 kg CO2-eq per kg of lettuce grown. (This paper does a nice job of showing the impact that energy source and LED efficiency has on potential environmental impact. For example, coal-powered vertical farms may emit 70 times more greenhouse gases than that of a vertical farm using wind or nuclear.)
We need to compare these carbon footprints to that of field agriculture. In the same paper, Romeo et al. suggests lettuce grown in the field has a carbon footprint of 0.29 kg CO2-eq per kg of lettuce grown. Kumar Venkat estimates a carbon footprint of 0.20–0.30 kg CO2-eq per kg of lettuce grown.
The literature suggests that lettuce grown in a vertical farm may have a carbon footprint that is at least within the same order of magnitude as growing lettuce in the field. If renewable energy sources (especially wind power) are used and LED efficiency continues to improve, it seems possible that vertical farms could reach a comparable carbon footprint.
I suspect that most vertical farms currently in operation, however, have not reached this point and are worse for the environment than field agriculture. If a Freight Farms unit consumes 150kWh per day and grows four tons of produce per year, the back-of-the-napkin calculation shows a carbon footprint of 10.7 kg CO2-eq per kg of produce. As of 2018, Bowery was still relying on grid energy, but was reported to be transitioning towards renewable sources. Aerofarms’s environmental impact report talks a lot about water savings and food miles, but doesn’t mention the source of their own energy.
Even if vertical farm emissions don’t quite reach levels comparable to field agriculture, the water savings, land use efficiency, weather independence, and shorter supply chain all offer compelling arguments for some adoption of vertical farms. Whether or not these vertical farms can be profitable is a whole separate question, as most today still rely on VC funding.
Venture capitalists seem to believe in the future of vertical farming, pouring millions into Plenty ($226M), Bowery ($168M), and BrightFarms ($113M). If investments in vertical farms were meant to be impact-driven, I would say these investments are misguided. The story may change if vertical farms can expand their scope to grow crops that traditionally have higher carbon footprints. Until then, agricultural investment would do more to advance climate resilience if directed at helping farms implement silvopasture, adopt regenerative practices, and replace annuals with perennials.