We travel to Colombia and Singapore to explore ways of helping the world's expanding cities to grow sustainably.

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.

earthrise travels to Colombia and Singapore to meet some of the people who are finding ways to meet growing demand while also making our cities more sustainable.

Colombia's Lego Homes

Over 300 million tonnes of plastic is produced every year, yet just a fraction of this is recycled. Most of the waste usually ends up in landfills, waterways and oceans.

However, one enterprise in Colombia has found a novel way of using the normally discarded waste. Conceptos Plasticos, founded by architect Oscar Mendez, collects recyclable plastic material, melts it down and moulds it into bricks which are then used to build houses for the local community.

The hope is that using plastic to build homes will be the answer to both recycling and housing shortages.

"If we use just two percent of the waste plastic in the world we can change the lives of millions of people. We can end the housing shortage in Latin America in just 10 years," says Mendez.

Juliana Schatz heads to Bogota to see how Conceptos Plasticos builds these homes out of discarded waste.

Singapore: Asia's Greenest City

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.

Source: Al Jazeera