By the middle of the twenty-first century, most of the world's population will live in cities. Growing food with the traditional methods that have been in use for thousands of years will no longer be sufficient to feed the world's expanding population. Humans have poisoned the food cycle by releasing toxins into the environment—into the air, water, and soil—and humans and other animals ingest these dangerous substances when they eat. The weakening of the ozone layer—Earth's primary protection from harmful ultraviolet rays emitted by the sun—and the effects of global warming, including crop-destroying droughts, floods, and hurricanes, add to the challenges we face. When food is transported in trucks from farms to cities, the diesel fuel that is burned is released into the atmosphere, further weakening the already damaged ozone layer.
One solution to these relatively new problems actually has a long history. Cultivating food under controlled conditions goes back hundreds of years, but it didn't become popular until the mid-nineteenth century, when technology made it possible to construct enclosed glass buildings, or greenhouses. Over the years scientists and architects have updated the traditional greenhouse with a variety of new technical features.
Perhaps the most promising innovation is greenhouses created for an urban environment—tall buildings that from the outside look virtually indistinguishable from office or apartment buildings, and are powered with wind and solar energy. These make locally grown produce available in an urban setting. An additional benefit is the promise of urban renewal. Neglected urban areas can be revived economically and socially by creating these new centers of sustainable industry.
And with greenhouses that can be as tall as twenty stories, a lot less land is used than with traditional farming. With no tractors involved, there's not only much less fossil fuel burned in the process, but energy is added back into the environment via the on-site composting of inedible parts of crops.
Some of the many other benefits include pesticide-free fruits and vegetables, since no bug control is necessary inside the greenhouses. Scientists have even come up with ways to grow plants in water without soil—a technology called hydroponics—and have now advanced to the point where they can just spray the roots with nutrients, saving water in the process. The runoff water, or "black water," used to hydrate the crops, can be easily recycled and even converted back into drinking water. Crops can be grown year-round, protected from seasonal ravages and the extreme weather conditions that are an increasingly common feature of the changing environment.
With time, ecosystems that have been damaged due to traditional "horizontal" farming—which often involves widescale deforestation and damage to the rainforest—might be repaired and reforested, and diseases contracted through unsafe agricultural practices—diseases that affect both farm workers and consumers—can be eliminated.
