Meeting Report

Worldwide, population growth is increasing the demand for food at the same time that climate change is altering agricultural patterns and suppressing some crop yields. The large-scale commercial agriculture we’re so heavily dependent upon uses chemicals intensively and has ruinous environmental impacts: nitrate-laden run-off is the largest source of water-body pollution. Long-distance food transport boosts our carbon footprint. And food safety problems related to commercial agriculture are a growing concern.

As more people move from rural to urban areas, cities have an ever-greater stake in securing adequate food supplies and in mitigating climate change. Together, all these factors point to a provocative question: Should food be grown on a commercial scale, using sustainable practices, in cities?

"Urban farming" is a term that still startles most of us. What would urban farming look like? What benefits could it deliver? How feasible is it? At a May 27, 2009, meeting presented by the Academy’s Green Science & Environmental Policy Discussion Group and Environmental Sciences Section, three speakers made a powerful cumulative case for shifting agricultural practices toward more sustainable, city-based models, and they described projects that could serve as models for more widespread strategies.

Putting cities on the map

Cynthia Rosenzweig has a keen interest in how climate change affects crops: she has a background in plant, soil, and environmental sciences. She also has a keen interest in cities, co-chairing the New York Panel on Climate Change and having helped create the Urban Climate Change Research Network. She works at the global scale, too, leading the NASA Goddard Institute for Space Studies Climate Impacts Group and contributing to the Nobel Prize-winning Intergovernmental Panel on Climate Change (IPCC).

Projections of temperature changes in the 2050s. "Climate change will affect people where they live in the cities of the world," Rosenzweig stated.

Work related to climate change often focuses on nation states, not cities, Rosenzweig observed. But cities generate about three-quarters of greenhouse gas emissions and are vulnerable to climate change. Cities thus have a major role to play in both adaptation and mitigation, she contends. For the mayors and citizens of cities, Urban Climate Change Research Network researchers around the world are writing an assessment report like the IPCC reports. "We call it 'the First UCCRN Assessment Report on Climate Change and Cities,' or 'ARC3,'" she said.

Climate change is affecting agriculture

World food crisis shows that cities are vulnerable.

Rosenzweig stressed that climate change “is not just in the future any more”: changes predicted decades ago are now occurring. Almost everywhere, the planet is warming. Because agriculture is a highly complex system, isolating climate effects is difficult, but studies have begun to document declines in crop yields, changes in crop growth stages, more pests, and the spread of disease. Other studies find significant effects on livestock milk production and reproductive success. Climate change also brings more frequent hot days and nights, more frequent heat waves, more drought, and more frequent heavy precipitation events, which can damage crops. And agricultural coastal regions are subject to rising sea levels.

These factors conspire to make cities vulnerable to rising food prices. After declining for decades after World War II, in 2003 food prices began to rise, spiking dramatically in 2007–2008 for the main commodities and dairy products, meat, poultry, palm oil, and cassava. While prices have since declined, they remain above former levels. Energy prices drove the spike, but climate contributed too; for example, drought in Australia has been attributed to an El Niño effect. The food price spike sparked "food riots in cities from Haiti to Bangladesh to Egypt; 37 countries were in critical need of food. And those critical needs . . . were in cities," Rosenzweig said.

The world food crisis offers an important lesson, she reflected: that "climate change is going to be one of many factors that come together in multiple stresses" to affect agriculture. New studies are needed to understand this complexity. Rosenzweig and others have begun working with crop modelers around the world to redo major studies, looking at climate change and the future of food. A very different picture of how climate change may affect agriculture will emerge, she speculates.

The New York bioregion

Climate change will affect growing conditions within New York City and in its foodshed, the region from which the city receives food. Projections show a rise in summertime temperatures of almost 3 °C by 2050, with more heat waves, floods, and droughts, and both decreases and increases in precipitation, with large uncertainties depending on decade and climate scenario. The New York Panel on Climate Change is creating climate change scenarios of record for the NYC region.

Urban agriculture is "an exciting set of methods" that in a variety of ways can help us adapt to climate change and mitigate greenhouse gas emissions, Rosenzweig believes. Growing plants, creating and recreating ecosystems, open space planting, street trees, green roofs, living roofs—all keep carbon out of the atmosphere.

Carbon sequestration potential of Hudson Valley farms based on soil type, farm size, farm type, and vegetation.

Another mitigation measure is reducing carbon emissions by shrinking the need for long-distance food transport. Glynwood Farm Center, located in Cold Spring, a small town north of New York City, is working to keep agriculture viable near the city. Together, New York City and the Hudson Valley, a diverse agricultural region with many smallholders, constitute an urban bioregion. Within it, a carbon sequestration program could also reduce carbon emissions.

Students at Barnard College estimated that if farmers converted from conventional tillage and heavy grazing to grass/legume pasture and no-till or rotational grazing, they could sequester an estimated 620,000 tons of CO₂ per year. Glynwood could assemble carbon credits and allocate the funds. Universities could verify that carbon is actually being sequestered by measuring soil carbon, modeling it, monitoring it, and developing an ongoing program. NYC citizens, businesses, and corporations could buy the credits, "nurturing agriculture and carbon sequestration in our own bioregion."

At $1.65 per ton (the price pegged on the voluntary Chicago Climate Exchange), farmers would be paid about $1 million a year for an ecological service. “An urban bio-regional approach can link New York citizens and surrounding farmers in climate change mitigation,” Rosenzweig concluded.

Rosenzweig views all mitigation measures as essential. "Basically, the problem of mitigating global climate change is so enormous that everyone needs to do everything," she stated. "We need to try everything." The most effective systems will ultimately emerge. "But every sector needs to do its part." Finding solutions in both urban and rural settings is essential.

"What if we can't farm outdoors?"

Dickson Despommier is pioneering a concept still in its infancy: the routine pursuit of commercial farming within the heart of cities. His vision is to conduct this not only on plots of ground but on tall buildings—and not only on rooftops but on building facades and in interiors.

Nature has no word for "waste."

Trained as microbiologist and now a professor at Columbia University, Despommier became interested in indoor farming as way of reducing the spread of parasites through food production. During a class he was teaching in 1999, a simple question arose: What do we do if, eventually, we can’t farm outdoors? When analyses of rooftop gardens revealed them to be an inadequate option, Despommier asked, "Why don't we just put [farming] inside?"

Despommier founded the Vertical Farm Project to examine how agriculture can be adapted and integrated into cities. Over the past decade, interest in the concept has grown steadily. He is convinced it will become a reality in the foreseeable future.

He grounds his conviction in the contrast between nature's biosphere with the man-made technosphere. "The world we arose from has no beginning and no end," he explained. It's an ecological system, and so you get a lot of recycling." In the technosphere, one problem is "what to do with what's left over after we've used something. You can call that 'waste,' but there's no word for that in nature. Nature reuses everything." We can learn from that, he contends.

Despommier's interest in vertical farming is not academic: it's a direct response to dire global conditions: worsening climate change, the challenges of meeting the basic needs of a surging population, and the damage agricultural runoff causes to the world's estuaries. Moreover, he explained, if, as projected, another 3 billion people are added to world population, the amount of additional farmland needed to feed them as we feed ourselves will be the size of Brazil. But 80% of the world's available land is already farmed. "So . . . how are we going to do this? That's the question."

The Vertical Farm Project

The future of agriculture is "growing soilless," Despommier contends. "We know how to grow food indoors. It's not difficult." We have all the tools we need: hydroponics, aeroponics, drip irrigation, waste-to-energy, automation, water recapture, passive energy, LED lighting—all proven technologies. They're just not all being applied in the same place. We can apply them to the city of the future in the not-so-distant future, he explained. "It's that simple. Take a high-tech greenhouse; stack 'em on top of each other, move them closer to where we live, and grow our food that way."

The Sustainable Eco-City

As that concept matured, he and his students explored energy use and the kinds of crops that can be grown indoors. (The NASA Web site yielded valuable data.) They found substantial advantages: no agricultural run-off, year-round crop production; no seasons; no crop loss due to severe weather events (droughts or floods); no fossil fuels used; and no pesticides or herbicides that damage ecosystems. Hydroponic farming uses 70% less water than conventional farming. In fact, "if water is the new oil," it can be made inside a hydroponic farm by recapturing the water of transpiration by dehumidification. A farm in Arizona is doing this now.

And that points to the biosphere model: perpetually “closing the loop.” Despommier cited other examples. In Santa Ana, California wastewater is being converted to drinking water. St. Lucie, Florida, proposes to run 1500 tons of solid municipal waste through a plasma arc gasifier that converts biosolids to energy. (The plan is controversial.) Santa Ana and Port St. Lucie should adopt each other’s innovations, he suggested.

San Francisco

In New York City a system that transformed wastewater to drinking water and generated electricity from wastewater biosolids would cost over $13 billion, Despommier said, with a return on investment in about eight years, and would generate 100 million kWh of electricity. Why do we waste those resources? "I guess, because we can," he speculated.

Above all, "I would like to give land back to nature," he said, in the form of trees. Planting trees—advocated by leading authorities—"is the first step in getting people to look at carbon sequestration in a permanent way."

Manhattan Rail Yards

Despommier showed many designers', architects', and artists' renderings of what vertical farms might look like. The one above by Ann Fougeron Architects depicts San Francisco as it would look in 2100 if everyone had a green roof and vertical farms were modular. Just before crops matured, large bins holding them would be stacked on ships and shipped off, ripening en route. Such imagined renditions stimulate us to consider the concept of vertical farms, Despommier observed, "and if you consider it, some version may exist someday."

He displayed inviting prospects in New York City: Floyd Bennett Field, with about five square miles of unused open space, and Governor's Island, which could exploit passive energy—wind, solar, tidal, and wave—to "create an urban landscape for agriculture."

The photo above lacks eye-candy appeal but may be the most tantalizing. The Manhattan 33rd Street Rail Yards could exploit solar and tidal power. "You've got this massive tangle of steel," Despommier said. "Just cover it over! Don't put Giants Stadium there. Give some vertical farms a chance. That'll actually work."

A practitioner's large view

What does it take to design and operate a successful urban farm? Ted Caplow has drawn from a background in mechanical and environmental engineering and expertise in integrated system design, renewable energy, water contaminant dynamics, and technology assessment to advance the field.

In 2004 he founded New York Sun Works in order to create the Science Barge, a floating, sustainable farm with a research and education mission. It launched in 2007, and its success spawned BrightFarm Systems, LLC, a design consultancy for which Caplow is senior partner, and Gotham Greens, a commercial urban farming company.

Caplow built the case for urban farming broadly, citing problems Rosenzweig and Despommier had cited, too, and adding several more. "Agriculture is the most important activity that we do on this planet and to this planet," he stated. It uses 60% of fresh-water withdrawals (about a ton of water is baked into a loaf of bread, he noted), is the largest source of water pollution, and the largest consumer of land.

By contrast, growing food in the city by means of a set of highly efficient sustainable technologies and methods—what Caplow terms building integrated agriculture—delivers benefits that span social, ecological, and commercial realms. "You don't need to cover the entire city," he explained. Growing all the fresh vegetables New York consumes would require 1.4% of the city’s surface area, or just 1/3 of the available rooftop area.

BrightFarm's work focuses on vegetables because the technology exists to grow them in cities, in an economically viable way. Rice and wheat could be grown, but the economics are very different. Moreover, vegetables are 90% or more water, so shipping them from remote farms is "really just shipping around a lot of water" at a high cost in carbon emissions. Vegetables must also be kept cold and shipped fast to avoid spoilage, while grain crops can be stored dry and shipped long after harvest. Growing vegetables locally yields far greater sustainability gains.

Beyond avoidance of "food-mile" carbon emissions lie other benefits. The biggest challenge to realizing them is energy management. "If real estate is about location, location, location," urban farming is about energy, energy, energy—and carbon, Caplow explained. Energy is expensive and becoming more so, and carbon emissions are the issue now. Placing a greenhouse atop a building creates synergies, reducing the energy both structures consume. The greenhouse shades and insulates the building; the plants within it lower temperatures through transpiration. And integrating HVAC systems means the greenhouse helps cool the building; the building helps heat the greenhouse; the greenhouse helps ventilate the building.

As another example of the synergies available to building integrated agriculture, stormwater retention systems built into the greenhouse capture rainwater that can be used to irrigate plants, avoiding discharges to storm sewers, which in New York City routinely overflow, polluting the estuary.

Hydroponics, Caplow stated, "is the enabling technology." Nutrients are added to water that is applied directly to plants' roots. Using no soil greatly reduces opportunities for plant disease. Recirculating systems use up to eight times less water than field agriculture, depending on the crops grown, and minimize the use of fertilizers. No chemical pesticides are required in a controlled environment. The waste stream is close to zero. Because the environment is controlled and nutrients are delivered directly to root systems, yields are up to 20 times those of field agriculture. So, while a greenhouse may look small, multiplied by 20, it's replacing a lot of field agriculture, and thus reducing land use.

Business advantages are substantial too: production is year-round, productivity is high, and middlemen are eliminated. Spoilage and waste during transport and retailing of produce are sharply reduced, because food is grown closer to the consumer. And the proximity of farmers to consumers promotes relationships that can command premium prices in the marketplace. For consumers, sustainable urban farming delivers safer, higher-quality, fresher food and better nutrition. "We're also making the city a nicer place to live," Caplow remarked. And of course, overall, urban farming serves the goal of self-sufficiency.

Pioneering a new commercial sector

Caplow's firm, BrightFarm Systems, is pioneering a new kind of business. Focused exclusively on "building integrated agriculture," the firm provides broad technical services in support of ecologically sustainable rooftop greenhouses—system design, resource analysis, feasibility assessment, engineering, equipment specification, crop selection, marketing and planning, business plan development, and commissioning, depending on the client. For commercial clients, that business plan is key: the project must be designed to produce not just produce but profit.

The ecological and economic factors that shape each project are depicted above; a typical web of relationships on a project, below.

The Science Barge, a floating greenhouse, uses recirculating water, hydroponics, an evaporative cooling system, a rainwater catchment system, and energy from solar and wind power and biofuels. Its ecological performance is impressive. The project has attracted 20,000 visitors, including 5000 students, and journalists from around the world. "Equally important, we've had a lot of engineers and architects and developers and city planners come on board and get excited about how this could apply to their work," Caplow reported.

For Whole Foods, BrightFarm created a small fresh-herb system inside the Millburn, New Jersey store. Caplow views food retail as an "extremely exciting" site for building integrated agriculture, and notes that the shorter food chain can both increase profit margins and minimize carbon emissions. His company is developing a concept design for covering an entire supermarket roof with a greenhouse.

For a NYC public housing project in the South Bronx, BrightFarm is developing plans for a six-story residential building with a rooftop farm. Integrating the two HVAC systems may result in a heat demand for the combined structures at or below that of the residential building alone. Among a number of school projects is one for NYC Public School 333: a rooftop retrofit to create the equivalent of "a Science Barge on a roof." The educational benefits are abundant.

Gotham Greens aims to be New York City's first commercial hydroponic rooftop farm. Located in Jamaica, Queens, and exploiting solar power and rainwater, this $1.4 million venture aims to produce 30 tons of high-value, low-food-mile fruits and vegetables a year. Whole Foods will buy about 70% of it for its NYC stores. Because local production slashes carbon emissions from transport, the New York State Energy Research and Development Authority awarded Gotham Greens $400,000 for a proof of concept project that larger installations can emulate. The project also won grand prize in the 2009 New York Green Business Competition.

Beyond rooftops, BrightFarm Systems is designing projects that would exploit the entire building envelope by deploying vertical farming systems on the facades. Long-term: as the scale of these projects grows, identifying heat sources within the built environment that can be integrated with greenhouses; for example, integrating greenhouses with industrial heat sources in cold climates. That is surely a hugely fertile field.

Open Questions

How will future energy prices affect the economic feasibility of scaling up urban farming?

What role will the urban consumer play in the development of urban farming? Will consumers actively seek out products that are “hyperlocal” and contribute to truly sustainable cities?

Will it take more than favorable economics to move urban farming into the mainstream? What kinds of projects, at what scale, in what mix will shift perceptions of it from fanciful to serious?

If urban farming gains traction, how will rural organic farmers and middlemen displaced by it adapt?

Fresh produce now dominates discussions of urban farming. What are prospects for other crops?

What waste-to-energy technologies will prove most cost-effective, and acceptable to the public? How rapidly will water shortages accelerate public acceptance of wastewater- to-drinking-water projects?

Will mobilization by the world's mayors to address climate change alter the political dynamic on other issues, too?

If the world’s cities do continue to grow, and clean-drinking water supplies shrink, and food prices rise, how adequately can they adapt? To what extent can they be "climate-proofed?"