Imagine a city of the future. Do you see clean streets, flying cars and robots doing all the work? Or something less rosy?

Cities cover just 3% of the planet's land surface, but are already home to more than half of its people. That means cities are bringing people into ever greater contact, where collectively they act as a giant physical, biological and cultural force. Transport links and communication between cities, from superhighways to express trains and planes, allow businesses to operate planet-wide, shrinking the human world and making the global local.

The great homogenisation of the Anthropocene includes human culture and lifestyle as much as any effect on the natural ecosystem. And cities are the biggest expression of that. They truly are universal. I feel at home in cities around the world precisely because they essentially provide the same experience. Some are more violent, or more sleepy, or more wealthy, but the urban environment is at its heart the same. There is not the vast diversity of landscape and experience that exists across the natural world.

The sheer concentration of people attracted by the urban lifestyle means that cosmopolitan cities like New York are host to people speaking more than 800 different languages – thought to be the highest language density in the world. In London, less than half of the population is made of white Britons – down from 58% a decade ago. Meanwhile, languages around the world are declining at a faster rate than ever – one of the 7,000 global tongues dies every two weeks.