The steel magnate Andrew Carnegie once said that the man who dies rich dies impoverished. He was America's first super-rich philanthropist.

Today the tradition started by him a century ago was given the biggest cash injection ever when 40 families and individuals all decided to meet the challenge posed by Warren Buffet and Bill Gates and give half their fortunes to charity.

Matt Frei spoke to Michael Green, the co-author of Philanthrocapitalism: How Giving Can Save The World.