We are living in a uniquely urban time in Earth’s history. In 1800, and for a thousand years before, just 2% of the world’s people lived in urban areas. Within the past five years, we have reached the point where more people are living in cities than in rural areas. By 2050, around three-quarters of the estimated 10 billion people on Earth will live in cities. It’s by far the biggest migration in human history, and it’s well underway.

So much so that the Anthropocene will be dominated by one species: Homo urbanus.

As a result, most of our species will live in artificial environments. The evolution of urban landscapes will be one of the strongest environmental changes to affect us.

Civilisation, that great loaded descriptor of human society, originates with cities. They have grown from the once vast Nineveh – home to 120,000 people in the ancient Assyrian Empire in 650 BC – to the Anthropocene’s megacities, defined as having more than 10 million inhabitants. There are currently almost 30 megacities on the planet (there were just three in 1975) – with the Tokyo metropolis, Japan’s national capital region, hosting over 35 million people at a population density more than double that of Bangladesh. By 2050, these megacities are expected to merge into dozens of megaregions, like Hong Kong-Shenhzen-Guangzhou in China, with more than 100 million people living in an endless city skyline.

The denser the city, the more productive, efficient and powerful it becomes. The theoretical physicists, Luis Bettencourt and Geoffrey West calculated that if the population of a city is doubled, average wages go up by 15%, as do other measures of productivity, like patents per capita. Economic output of a city of 10 million people will be 15-20% higher than that of two cities of 5 million people. Incomes are on average five times higher in urbanised countries with a largely rural population. And at the same time, resource use and carbon emissions plummet by 15% for every doubling in density, because of more efficient use of infrastructure and better use of public transportation.

The urban revolution of the Anthropocene could prove to be the solution to many of our environmental and social problems, allowing humans to inhabit the planet in vast numbers, but in the most sustainable way. Or, it could finally prove to be our species’ undoing, the apocalyptic version of the dystopian megacity so often portrayed in science fiction.

Urban re-think

Whether the cities of the Anthropocene will be environmentally sustainable or not depends on how the slum districts of developing world cities evolve. Will cities follow the inefficient North American model: suburban sprawl of highway-linked satellite towns, or rather the closely packed high-rises of Hong Kong and Singapore? Seoul is one example of how a city can transform in a couple of decades – from a filthy slum in which one-third lived in low-rise squatter settlements, to a shining functioning city of metro-linked skyscrapers in which most of the 25 million population live in healthy surroundings.

Apart from a few examples, most cities were never designed or planned, they grew - sometimes over thousands of years – in an ad hoc pattern. Occasionally, sections would be entirely rebuilt according to architects’ plans, but these opportunities were usually the result of disasters, such as earthquakes or bombings, or because of grand schemes, such as slum clearance, industrial development or large-scale municipal constructions, such as a new highway or transport system.

Now architects are having to re-think the city in the age of high population, strained resource use and global environmental impacts. In some places, such as Tianjin in China, planners are designing entirely new cities for the Anthropocene, trying to avoid errors of the past and achieve a sustainable solution from the outset.

Most cities will have to be retrofitted for the new urban age to allow them to accommodate more people and function efficiently with lower carbon emissions. In my next few columns, I'll be exploring some of the tactics cities are using to meet these multiple challenges and create truly liveable, human habitats. I'll be looking at slums, integrated transport, networked “smart” aids, water and energy provision, and green architecture construction.



Before I do, it’s important to note one point. As hubs of industry, transport and domestic and office buildings, cities consume a large proportion of global energy and generate more than 80% of carbon emissions. This geographic concentration of such a hefty proportion of emissions actually presents an opportunity for easier fixes. The more compact the city, the more energy efficient transportation and everything else is.

Reach for the skies

While suburbia was built around the automobile, the city of the Anthropocene needs to be built around efficient, low-emitting mass transit. But to fit 6 billion people into cities by 2050, they will have to rise upwards and reach the sky. These cities will increasingly feature skyscrapers connected by sky-bridges and corridors, served by elevated mass transit, with above-ground parks and gardens.

We’ll also make more use of underground space, already so riddled with cables, pipes, sewerage, subway lines and basements that fossil-hunters of the future will wonder what enormous creature burrowed and ate its way through the Earth to leave such tunnels. Some cities, such as Singapore, already have vast networks of malls descending several storeys under its streets.

But cities have always defined themselves by their skylines, whether the vast gold-plated Mayan temples of pre-Colombian America, the Dome of the Rock in Jerusalem, the mythical Tower of Babel, the steeples and spires of Europe or the Empire State Building in Manhattan.

The new cities of the Anthropocene are continuing this trend – more than 350 skyscrapers have been constructed since 1999, when Malaysia unveiled its twin Petronas Towers, then the world’s highest building. By 2016, the Petronas Towers won’t even merit a spot in the top 10. The current tallest building, at over 828 metres (2,716 feet), is the Burj Khalifa in Dubai, a sky-piercing structure of such immensity that it bears no relation to the human-proportioned Bedouin huts that peppered this location just a few decades ago. Three-quarters of the world's tallest buildings are now in Asia and the Middle East, over a century after the first skyscraper opened, half a world away in Chicago, then New York.

Scaling up doesn’t have to be as ostentatious as the Burj Khalifa, but it can be as innovative. Architects are using new materials, such as steel reinforced concrete, and new techniques, such as computer modelling, to see how their buildings will function when complete – for instance, how people will move around, live and relax in these towering houses. It allows them to tweak their designs early, such as improving escape routes or optimising apartment views and sun penetration. Cleverly designed, complexes holding thousands of people needn't feel crowded or cramped. Some skyscrapers attract birds and wildlife to sky-gardens, tens of floors up.

But in order to improve the sustainability of skyscrapers, architects need to go beyond the not-insignificant economy of scale achieved to include low-energy innovations. The Bank of America Tower, which opened in 2009 in New York City, achieves just that. It is made largely from recycled materials, captures its own rainwater and conserves water in other ways, such as with waterless urinals. It filters incoming and outgoing exhaust air, produces two-thirds of its own energy using an onsite, gas-fuelled combined heat and power generator, and conserves energy with insulating glass and “ice-batteries” in the basement, a system that uses off-peak energy at night to freeze water and allows it to melt during the day to cool the air in the building. The office tower has won a slew of awards and been given a platinum (highest) LEED (Leadership in Energy and Environmental Design) rating.

In the Anthropocene, buildings will need to incorporate features like these, and also meet our human needs in a liveable space, including sociability, calm, recreation and ease of movement. And do this hovering tens, if not hundreds, of storeys above the ground.

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