Hong Kong's got an unreasonable amount of people living in unreasonably small spaces. And Dr Merrin Pearse's on a mission to make the metropolis continue.

Pearse was described as an urban vigilante for HK sustainability. He's an advisor at Purpose Business, and chair at the Living Islands Movement (a local group dedicated to the sustainable environment of the outlying islands). He also founded a consultancy helping companies achieve their sustainability goals.

He told us what the city's doing well, the biggest challenges it faces, how we can help, and which part of recycling is full of literal gold.