Cities have long held the promise of 'streets paved with gold'. Today, nearly half of us live in urban areas; by 2030, two thirds of us will. The world's cities are currently home to more than 3 billion people and are growing by 1 million people a week - 100 new residents every minute.

Although cities occupy just 2 per cent of the earth's land surface, their inhabitants use 75 per cent of the world's resources. But cities are economic powerhouses, too, generating more than half the world's wealth and, in some developing countries, up to 80 per cent of their economic activity. On average, urban dwellers earn higher wages and live healthier, easier lives than their rural counterparts.

The benefits are not universal - as many as 1 billion people live in slums and squatter settlements with limited access to clean water, sanitation, adequate housing, transport, schooling or health care. For them, city life is marked not only by opportunities but also by poverty, overcrowding, disease, violence and uncertainty, with survival depending on their astonishing personal resilience and resourcefulness.

The growth of modern cities has far surpassed the mass migrations of the past. People will still flock to them as long as urban living conditions outstrip those in the countryside. For the first time in history, humans are becoming predominantly urban. Might our mindsets and lifestyles decreasingly comprehend the values and vital services provided by natural world? A challenge for us all, as - from towns to mega-metropolises - the urban revolution is here to stay.