Urban farms also increase vegetation cover – a key way to limit rising temperatures. They reduce the ‘urban heat island effect’, where cities are often several degrees warmer than nearby rural areas due to heat trapped by dark-coloured roads and buildings, researchers said.

Urban farms can lower the risk of flooding during heavy downpours and help to reain water in dry areas, according to a paper published in the journal Earth's Future.

In developing regions, ‘urban agriculture may be critical to survival or a necessary adaptation to changing climate’, said the team of researchers, led by the Arizona State University and Google.

Urban farms could supply almost the entire recommended consumption of vegetables for city dwellers, while cutting food waste and reducing emissions from the transportation of agricultural products.

The researchers analysed multiple datasets in Google Earth Engine, an internet platform for processing geographical data, to derive global scale estimates.

Urban agriculture has the potential to save energy equivalent to the use of air conditioners in nearly 9 million United States households, and to produce up to 180 million tonnes of food, they found. While this represents only about 10 percent of the global production of pulses, roots and vegetables, it provides ‘a partial solution’, said Matei Georgescu, associate professor at Arizona State University and co-author of the paper.

The US, China, Brazil, India, Russia, Germany and Japan have the most potential benefit from urban farming. With more than 2 million hectares, the US has more urban area available than any other country.

Georgescu said he hopes urban planners in Africa and Asia will see the potential of urban agriculture too.

According to the United Nations, two-thirds of the world's population may live in cities by 2050, with new urban areas concentrated in Asia and Africa.

Georgescu also encouraged people to calculate this potential for their local areas themselves using method provided in the paper.

"One simply has to include their own locally produced data, which might be better than the global data we had to use, and produce their own estimates," he told the Thomson Reuters Foundation in a phone interview.

Urban farms have become popular in recent years as governments and residents look to promote healthy eating, tackle environmental challenges and transform industrial cities.

Pittsburgh is establishing the largest urban farm in the US, post office workers in Paris are growing vegetables and breeding chickens on a rooftop, while a warehouse in London is farming fish and greens.

Source: Reporting By Thin Lei Win, editing by Jared Ferrie of the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, corruption and climate change. Visit: www.trust.org