A man sleeps between tombstones in front of his single-room home on a hot night in the Cairo Necropolis, Egypt, October 13, 2015. In the sprawling Cairo Necropolis, known as the City of the Dead, life and death are side by side. Amid a housing crisis in Egypt, and with the population of greater Cairo estimated at about 20 million, people count themselves lucky to have a place to call home in the graveyards that date back hundreds of years. (Photo by Asmaa Waguih/Reuters)

Kale grows at Kajodlingen farm in Gothenburg, Sweden, September 28, 2016. They are doing it on the rooftops, on tower block balconies and even on a disused railway: Swedes have discovered a passion for urban gardening as a way of growing fresh food and getting back in touch with nature. Part of a global movement, an increasing number of Swedish city-dwellers are growing their own in window boxes and allotments or are visiting public gardens built in or on industrial or office spaces. (Photo by Maxim Shemetov/Reuters)

These are the ambitious plans which suggest skyscrapers of the future may house an entire city. The Endless City project is an award-winning proposal by sure Architecture, who propose turning skyscrapers into complete ecosystems. London is the proposed city for the mixed-use tower – which would feature huge ramps linking different sections of the structure. The company, whose design won the SkyScrapers and SuperSkyScrapers Competition, insist the structure would be a great space-saver in dense cities which have previously spread outwards rather than upwards. (Photo by Caters News)

Circus performer and trampolinist Max Calaf Seve performs at a preview for NoFit State Circus new summer show at the Eden Project on March 29, 2012 in St Austell, England. This will be the second time that the NoFit Circus has performed in the world famous biomes of the Eden Project. The production will start on July 28 and run until September 2 before leaving Cornwall for a global tour. (Photo by Matt Cardy/Getty Images)

Young Japanese women pose with a green bear costumed person during the 'Earth Parade 2015' in Tokyo, Japan, Saturday, November 28, 2015. Ahead of the U.N. climate change summit in Paris starting this week, about 1,000 citizens and environmental activists took to the streets of Tokyo on Saturday, calling for strong actions to combat global warming. (Photo by Franck Robichon/EPA)

The Grevy’s Illusion by Yaron Schmid, USA: a Grevy’s zebra staring at the camera in Lewa, Kenya. Third place – wildlife. (Photo by Yaron Schmid/The Nature Conservancy Global Photo Contest 2019)

This photo taken on March 29, 2017 shows a young woman offering shots of liquer at a dance bar in Walking Street in Pattaya. Two hours east of Bangkok, Pattaya' s bawdy reputation hails from the Vietnam War era when US GIs partied in their downtime. (Photo by Roberto Schmidt/AFP Photo)

Water is seen on part of the glacial ice sheet that covers about 80 percent of the country is seen on July 17, 2013 on the Glacial Ice Sheet, Greenland. As the sea levels around the globe rise, researchers affilitated with the National Science Foundation and other organizations are studying the phenomena of the melting glaciers and its long-term ramifications. The warmer temperatures that have had an effect on the glaciers in Greenland also have altered the ways in which the local populace farm, fish, hunt and even travel across land. In recent years, sea level rise in places such as Miami Beach has led to increased street flooding and prompted leaders such as New York City Mayor Michael Bloomberg to propose a $19.5 billion plan to boost the citys capacity to withstand future extreme weather events by, among other things, devising mechanisms to withstand flooding. (Photo by Joe Raedle)