Does it really stack up?

摘要

When you run out of land in a crowded city, the solution is obvious: build upwards. This simple trick makes it possible to pack huge numbers of homes and offices into a limited space such as Hong Kong, Manhattan or the City of London. Mankind now faces a similar problem on a global scale. The world's population is expected to increase to 9.1 billion by 2050, according to the un. Feeding all those people will mean increasing food production by 70%, according to the UN's Food and Agriculture Organisation, through a combination of higher crop yields and an expansion of the area under cultivation.