There is an optimistic view of the unprecedented migration we are witnessing from rural to urban areas, and it’s that cities could offer the biggest hope for the survival of other species and ecosystems in the Anthropocene. Cities are entirely shaped and created by humans to protect and separate them from the natural world, allowing selected bits in and banishing others. If humans – and their landscapes of concrete and glass, and their industrial sprawl – are kept within the confines of a megacity, the rest of the planet should be free to rewild, to revert to a more natural state.
There’s one major problem with this. Cities do not exist as islands in isolation. They consume food from vast tracts of farmland, timber from the forests, minerals scraped from the Earth, water that drains rivers, fish from the oceans, and energy which requires the plunder of yet more land. Depending on how resource hungry its citizens are, a city can use areas of land many factors larger than its own footprint. Robert Krulwich at NPR makes a great comparison of how cities use land area. A megacity that housed the entire population of the world at a similar concentration to a dense city like Paris would occupy around 350,000 square kilometres, or three US states. But if these citizens lived side-by-side in ranch houses, they would require a further four planets-worth of land to satisfy their resource demands.
It is also uncertain how permanent many new megacities are. As many countries develop, low-density suburban sprawl and the take-over of wilderness will march across the world at unprecedented pace. No one, after all, imagines living cheek-by-jowl in a slum as anything other than a temporary measure en route to better things.
Currently, urban areas cover around 2% of the planet’s land area, but by 2030, they could stretch to almost 10% of the world's land surface. That means losing some 1.2 million square kilometres of other landscapes to urban construction alone, many of them rich in biodiversity. The Amazon, for example, is currently experiencing Brazil’s most rapid rate of urbanisation and is already home to 25 million people.
So if the environmental preservation opportunity that cities offer is to be realised, then the citizens of the Anthropocene will need to live far more efficiently than most city dwellers currently do.
Cities will need to incorporate the natural world in new and innovative ways. Parks and green spaces will be multiplied from ground level upwards, attracting birds and wildlife to sky-gardens, tens of floors up. In Singapore, for example, the Marina Bay Sands hotel features a skypark on the 56th floor, with trees, leisure facilities including a pool, and far-reaching views. It’s an example of how specific elements found in the natural world, such as a mountaintop view, a lake and palm trees, have been cherry picked and combined to provide an easy, entirely artificial landscape for the city.
Vertical farms are also being planted in Anthropocene cities, although the energy involved in irrigating and maintaining such farms makes them impractical for food production on a larger scale. However, growing food in the urban environment on regular multi-storey plots is likely to increase as hobby farmers, beekeepers and specialist growers take advantage of cleaner air, water and soils of Anthropocene cities, and vacant sites are used more effectively. In Berlin, rooftop fishfarms have been started, with the waste going to feed agricultural plots in the city. Creative growers are already converting industrial spaces, street corners and rooftops to micro-wildernesses or manicured into formal gardens. A disused raised railway in New York City has become a popular park, self-styled “guerilla gardeners” are planting flowers and trees in plots among the tarmac and traffic of London’s highways, and once-polluted industrial wastelands now chirp with birdsong, rivers swim with fish and populations of animals that have become rare in the countryside are thriving in urban niches.
There is already a new field of urban ecology for scientists who study the city and biophysical interactions within it, in a similar way to traditional ecosystem research. In fact, a surprising amount of wildlife now depends on the human-made environment, from the clouds of huge Sydney fruit bats to London’s wily foxes, to skyscraper-nesting peregrine falcons, animals have made cities their home - in some cases, their natural habitats have disappeared. In other places, the mix of human-introduced plant and animal species, and those opportunists that migrate to the urban environment, are interacting to produce unique ecosystems that exist nowhere else. Seagulls, for example, now often live in cities hundreds of kilometres from the coast. As their traditional food – fish – becomes scarcer, they scavenge human rubbish.
Whether traditional conservationists and wildlife lovers learn to value these new flourishings that are occurring at such a rapid rate is still to be seen. But what is certain is that the survivors of these menagerie experiments in the human garden will produce a genetic legacy. In centuries to come, new species that could not have formed under pressure from any natural circumstances will be testimony to our mixing. Already, urban moths have evolved changes in shade suiting their dull concrete habitat (compared with the tree trunks they used to live among), songbirds have got louder to compete with traffic noise. And, as many city dwellers know, there are now new varieties of urban rat, housemouse and cockroach.