Rafal Hejne describes research into the sustainability of five of the world's biggest cities.

By 2050 70% of the global population will be living in cities which will be required to accommodate an additional 3.1 billion people. It is hard to believe but in 1950 there were only two megacities (New York and Tokyo). Sixty years later, in 2010, we have at least 26 megacities (cities with more than 10 million residents). By 2015, the number of megacities is expected to reach 33 with 27 in developing countries. Loving cities myself and devoting my career to city management I decided to learn more about this fast-paced change.