THE world's boldest and often most interesting cities are pacesetters, pioneering new solutions to population density and space limitations, showcasing new architecture and applying technological innovations that spread far beyond the city limits. Above all, they are efficient in every sense - and the most efficient cities are those where innovation plays a leading role.

Today's cities, embedded through socio-economic means and modern technologies in vast networks, are also increasingly global. These networks, with their myriad nodes and linkages, both physical and formless, have quickly become a prerequisite for economic development and growth.

Global networks of cities have transformed the relations of economics and ecology into forms that are still barely understood. The very opportunities that a city prides itself on offering also constitute one of its greatest challenges. Urban dwellers' aspirations for more space and better housing generally result in further pressure on the city's environment. The mega-city phenomenon that characterizes much urban development in the developing world not only exerts tremendous stress on the environment but also incurs significant costs, both for individuals and for society as a whole. Many of these cities are barely habitable, by other standards. They are crowded, unhygienic and dangerous. Slum dwellers further suffer from a lack of durable shelter, reliable access to safe drinking water, proper sewage systems or any of the other benefits of city life. The mega-city - and the potentially disastrous environmental and socio-economic consequences of its labor-seeking migration, competing land uses, and air and water degradation - is a microcosm for the planet.

Significant global climate change, water shortages and the need for cleaner and renewable energy sources require a new approach to urban development. Cities of the future will need to be increasingly interconnected yet also more self-reliant. Renewable energy enables a city to reduce its dependence on fossil energy and its ecological footprint. Renewable energy production that occurs within cities, integrated into their land use and man-made environment, can be a key driver of the urban economy. Urban planning can thus contribute to global sustainable development through strategic applications of technology and management at the local level. Innovation in this regard is important in creating the kind of eco-efficiency gains that are required.

In global cities, the most effective and efficient way of providing energy has traditionally been through larger centralized production facilities and extensive distribution systems. However, renewable energy-driven, low-carbon cities may employ a decentralized energy production model, whereby energy is produced closer to where it is consumed, and indeed often directly by those who consume it. This distributed form offers a number of benefits, including energy savings, lower vulnerability and greater resilience in the face of natural and man-made disasters. The same approach can be applied to a city's water systems. Some of the small-scale, local water systems that have proven effective employ nanotechnology applications in the purification and treatment process.

Experience has shown that cities can best tackle environmental issues through a strong planning system that ensures cooperation and communication at the local, municipal and national levels. Urban planners can make cities more efficient and liveable by planning and investing holistically in building construction, transport, energy sources, communications, water management and sanitation. Their challenge is to combine new technology, city design and community-based innovation, for example in creating the infrastructure needed to support solar and wind power on a scale sufficient to power a city.

Such green initiatives have already begun to emerge around the world. In order to accommodate a projected doubling of the population while also resisting further outward sprawl, the San Francisco Bay Area has designed a new infrastructural network that is able to collect and distribute water, power, fuel and goods, and to accommodate the transport of residents and tourists alike. In Europe, 30 cities have been selected as pioneers to deploy high-tech energy systems, with half of the power grid able to handle renewable energy using "smart" systems. Such high-tech solutions to climate and energy challenges are aimed at giving European businesses a head start as the world switches to low-carbon energy. These "smart cities" will be the nuclei from which smart networks, a new generation of buildings and alternative transport means will develop.

The choice of Shanghai as host city for World Expo 2010 is eminently appropriate. Shanghai is a city that has made itself global by employing state-of-the-art technologies in urban planning. In becoming one of the centers of the world economy, Shanghai - vibrant, handsome and resolutely modern - has experienced faster growth than any other global city in the past 15 years. This rapid growth has produced many of the problems common to other mega-cities. The city has had to cope with population increase by physically increasing in size, through the development of neighboring areas and satellite towns.

The urban eco-efficiency agenda is crucial to ensuring a green and sustained global urban future. Much work needs to be undertaken in sustainable urban development by the global and local communities of planners, politicians, environmentalists, the private sector and civil society - especially in the developing world. And if the cities of the developing world are to be green - if they are to survive - they will have to draw heavily on innovation.

The World Expo Shanghai is certain to serve as a springboard for further innovations and solutions in creating the green global cities of the 21st century. We are thus honored to contribute to the event and to its worthy goal - "Better City, Better Life."