Cities around the world are growing, and their growth presents a problem for global climate change.

On one hand, cities require huge amounts of gasoline and other carbon-based fuels to function. Coal power and natural gas power homes and businesses. Gasoline and diesel vehicles move city residents through packed highways and city streets. Food to feed cities must be transported thousands of miles from distant farmland to urban markets.

On the other hand, Cities are hot! They pump out and store immense amounts of heat. Concrete roadways, parking lots, and black tar roofs heat up and store heat throughout the day. These surfaces retain enough heat to keep nighttime temperatures from cooling off. Car engines are like small furnaces warming up the surrounding air. Air temperatures in urban areas can be up to 6 degrees Celsius hotter than nearby suburban and rural areas. Scientists use the term “heat islands” to refer to this phenomenon.

A solution to solving both of these problems is to redesign urban food systems for urban agriculture, and many farmers are creating new and innovative technologies to do just that.

A recent article in The Atlantic highlights new technologies that enable farmers to grow crops vertically. Bright Agrotech, a startup located in Laramie, Wyoming, has designed an easily assembled and highly productive system for growing crops vertically. The design uses plastic “towers” filled with a lightweight growing medium and a long slot cut on one side of the tower out of which plants grow. The towers are designed to be placed along outdoor walls and fences, and they can even be used to fill an entire greenhouse with vertical crops.

Vertical growing makes it possible to construct large gardens on limited land area, and available land is hard to come by in many cities.

A much more common practice in urban areas is window, terrace and rooftop farming. Plants can be grown in pots, buckets, and planter gardens placed almost anywhere that the sun shines. Window farming is a technique for growing plants in recycled bottles hanging inside a window. For some, building a window farm may be too complex to assemble. A window-hanging planter box may be a much simpler alternative. Many urban farmers are also using 5-gallon buckets to grow everything from tomatoes, corn, to watermelon.

All of these are innovative ways to make use of limited space in urban areas, and each can play an important, even if small, role in helping to transform urban food systems.

None, however, hold as much potential as large-scale, rooftop farming. Many urban areas have thousands of acres of unused rooftop space that could be put into food production. Urban farmers are transforming rooftops in Kolkata’s new apartment complexes into vegetable farms. New York City is home to innovative farms like Brooklyn Grange that use the space on converted warehouse rooftops to supply local restaurants with produce.

Rooftop farms have an added advantage of helping to save on energy costs as well. During hot summer months, plants and soils absorb the suns intense rays and keep buildings from overheating. The plants reduce the amount of energy and money needed to air condition large buildings. In the winter months, rooftop soils help to insulate buildings and lock in heat. Rooftop farms could be an important solution to minimizing the effects of heat islands in urban areas.