This is humankind's 'great urbanisation'. We must do it right, or the planet will pay

The world will never again build cities as rapidly as it does this century. If we are serious about limiting global warming, tackling air pollution and promoting innovative, resource-efficient growth, there is a narrow window of opportunity

Almost as staggering as the current enormous influx into cities across the globe is the dramatic slowdown in urbanisation that will follow it. The world is literally going to town on urbanisation - but it is a project that is both immense and historically fleeting.

In less than 100 years, the world's urban population is expected to double to 8 or 9 billion - accounting for the bulk of a projected global population of around 11 billion. Yet in all the centuries that follow this one, cities may add, at most, another billion to their ranks. So if this century is the most urbanising in history, it will also mark the end of humankind's "great urbanisation" era.

Humans work best in cities " but urbanisation also creates pollution, congestion, poor health, crime and waste

Corruption stifles incentives to work and innovate " and risks rendering cities dysfunctional

Related: Climate change and cities: a prime source of problems, yet key to a solution