Buildings are among the biggest wasters of energy on the planet. This programme looks at the alternatives – and visits what are being billed as some of the greenest buildings in the world. At the moment almost 40% of all global greenhouse gas emissions come from buildings. In the more intense urban areas, like New York and London, it’s nearer 70 per cent. Designing and constructing buildings that are eco friendly has never been more important. Skyscrapers and other commercial buildings are the worst offenders. Often, the buildings have been designed for show and with little consideration for the environment. But some architects have been going in the other direction, designing buildings that run as complete ecosystems with little external energy supply, using elements of nature such as walls of plants and green roofs, the sun, breeze, shade and water.This programme goes to Singapore, Germany, the USA and the UK to look at green designed buildings.