The crystal ball says the future is bright if politicians, scientists and businesses work together. In an ideal world, politicians take a problem and change it into an opportunity. Businesses provide the capital and processes. Scientists deepen our understanding of society and develop the technology required. In a rapidly urbanizing world, these three come together to create sustainable cities. These utupian places have people living in harmony, with small carbon footprints and plenty of energy, water and good health.

At least, this is what the panelists who opened the Third Future Dialogue conference on "Sustainable Cities - Mastering the Challenges and Opportunities of Rapid Urbanisation" in New Delhi, 24 September, 2011, felt. Cornelia Pieper, Minister of State, Federal Foriegn Office, Germany, said big cities have major problems of mobility, without accelerating climate change. They also had problems of providing health care, education and water for rapidly growing populations. "But huge challenges come with big opportunities," Ms. Pieper said.

There are compelling reasons for making cities sustainable. With half the world' population, cities produce 80 per cent of greenhouse gas emissions. They use 75 per cent of the energy produced. More than half their population lives in slums. Many have irregular water supply. The poor do not have good schools, hospitals, or, as most speakers felt, transport. Transport seemed to be the trump card in making cities sustainable. But more on that in a little while.

So for emerging cities, sustainability is a must. Sustainability as in adequate and good public spaces and public transport that is preferably off-road such as trains, metros or monorail systems. The unspoken sub-text from this was, cities in India have to find their own formula for sustainability, different from American cities or even European ones. But the European model powered by efficient non-road based public transport systems is the best. Technology is the solution for this development conondrum, through which India's urban cities can find their optimal growth trajectories. Barbara Kus, Chief Sustainability Officer, Siemens AG, Germany, tempered technology with "its effective implementation depends on favourable conditions".

So what are these conditions. The most important, according to Nicholas you, Chairman of the Steering Committee, World Urban Kenya, is appropriate governance. "Cities are spread over multiple authorities who do not look at the city as a single entity. Cities are parcelled out, politically, geographically and technologically. Good cities were those historically that were well planned and looked after by a single authority."

He gave the example of Manhattan. A slide shows Manhattan in 1811, when its original team of three planners drew straight lines for streets. "New York has an equitable plan as people in all blocks have equal access to public spaces and can procure services within walking distance. It is efficient. This demonstrates the three pillars of sustainability - society, economics and the environment. Most importantly, 36 per cent of the city was given over to streets.”

That brings us back to transport, or more widely, access. In Mumbai's slums, spaces for public movement (they cant be called streets or lanes) occupy a mere 0.6 per cent of the total area. This, said Jon Clos, Executive Director of UN-HABITAT, is the reason why poor cities collapse. It may be pointed out that 60 per cent of Mumbai's population lives in slums. By contrast, in the developed world, roads occupy 30-32 per cent of the total space. Once again, this shortage of mobility space is due to bad planning, in turn due to bad governance. “To have a city, you need a pattern of public and private spaces. Public spaces are the founding infrastructure of a city.”

Another condition, said Sumila Gulyani, Head of the World Bank's Urban Knowledge Platform, is inclusion. One of the most powerful drivers for inclusion is security of land tenure, including for those living in slums. City authorities have to recognise slums and provide security of tenure. This is the biggest driver for providing slum-dwellers with basic services and raising their standard of living. It is tied to the quality of housing, water, sewage, education and health care. The Bank is planning to share information on this and other aspects through the Urban Knowledge Platform, that, she said, “Will connect policy makers with practitioners and researchers around the world. It will also make the Bank's data available to all.”

Another powerful driver for urbanisation, and inclusion, is migration. Steven Vertovec, Director of Max Planck Institute for the Study of Religious and Ethnic Diversity, said a sixth of humanity was on the move. There were 214 million international and 740 million internal migrants in the world, mostly headed to cities. But the resulting diversity was not the problem in cities, inequality was.

Robert Neuwirth, author of Shadow Cities: A Billion Squatters, questioned this paradigm of sustainable cities. The constituency for sustainability has to be drawn from the people living in the cities. While sustainability is an idea, ideas don't change the world, people do. Many people living in cities are poor, and continue to be excluded from services. Thus, a garbage dump can be called sustainable since it supports hundreds of people. He threw out a question, that nobody picked up. “Is sustainability sustainable?”

From the morning rounds, the outlines of challenges that cities in developing countries faced emerged. Also, the contours of possible solutions started to drift into sight, notably the cities need public spaces and efficient public transport. What was unchallenged was the inexorable rise of urbanisation in the developing world.