Half the world's population live in cities, and by 2050 the figure will increase to two-thirds, or about six billion people. The environmental impact is already extensive.
As the global population expands, so too do pollution and pressure on resources.
Known as Asia's greenest city, Singapore has long favoured innovative environmentally friendly ideas.
However, challenges from rapid urbanisation, sea level rise and a changing climate are pushing planners and policymakers to find innovative ways of coping with the pressures of growing demand.
From vertical farms to living buildings, Singapore is on the cutting edge of environmentally sustainable urban solutions.
Russell Beard travels there to meet some of the entrepreneurs who are helping the island city-state earn its green title.
'earthrise' is an award-winning series exploring solutions to the environmental challenges we face today.
The programme takes an upbeat look at ecological, scientific, technological and design projects all around the world, from a group of Dutch architects who design stunning buildings made from waste materials, to an ingenious project that has dramatically cut rhino poaching on a South African game reserve.