Achim Steiner, born in 1961 in Brazil, is the Executive Director of the United Nations Environment Programme. An expert in environmental politics, Steiner grew up in Brazil and was educated in England at Dover College. He studied philosophy, political science and economics at the University of Oxford.

Since the first Expo in London in 1851, world fairs have given visitors a taste of the future and the progress of human societies. The Shanghai Expo follows this historic trend around the theme: "Better City, Better Life."

But what is a "better city" in a world where the sustainability of urban living exists in a finite reality? Like many large and rapidly developing cities, Shanghai has faced the challenges of ensuring fresh air, clean water, sustainable energy, efficient transport and waste reduction for its 20 million residents. No small challenge.

Yet nine years since accepting to host the Expo, this ancient trading hub today boasts Asia's first offshore wind farm, the largest solar power plant in China, a world-class 400-kilometers rapid transit network and a new fleet of energy vehicles.

For the more than 70 million expected visitors, the Expo's legacy will show us a modernity that is green, sustainable and achievable.

Expo tributes from 100 eminent voices