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The data shows that at present over 50% of the population in the world have already lived in cities， and by 2030， nearly 60% of the population in the world， namely about 5 billion， will inhabit in cities. Sustainable urbanization is therefore becoming the more urgent challenge faced by the global society in 21st century. As the first international day in relation to cities， and also the first international day initiated by Chinese government， the designation of "World Cities Day" will focus on the development issues of city and pay attention to the efficiency improvement and technology innovation in the process of global urbanization， aiming to carry out effective management in cities with population agglomeration， reduce resources and energy consumption， and achieve an orderly and healthy growth of cities.
The predicted population of 10 billion by 2100 （some even predict 11 billion） and the rapid growth of megacities will throw up many challenges. These growing cities will need major infrastructure to cope and it is easy to wonder whether future cities will be places of chaos and inequality， with shortages of essential services， energy and food.
The challenges are great. Tackling CO2 emissions is probably the most urgent and difficult challenge in the Anthopocean era， as we are currently producing more CO2 than the Earth’s ability to absorb it. As almost all city activity is responsible for greenhouse gas emissions （the UN estimates cities to be responsible for 70% of global CO2 emissions） society will have to find new low carbon solutions. There are many fanciful ideas about engineering our 7way out of the climate change predicament， such as fertilising the oceans to encourage phytoplankton to absorb CO2 or peppering the stratosphere with trillions of reflective discs to deflect the sun’s rays， but the more reasonable approach will be to find carbon neutral solutions for our cities and to modify our behaviour somewhat.
The rate of growth of cites is staggering; we currently have 10 megacities （over 10 million population）， but in the coming decade this will rise to 37， two of which will have over 40 million inhabitants. There will be rapid migration from dispersed rural settlements to cities; the current 50-50 split between urban and rural populations will rise to 60% living in cities by 2030 and 70% by 2050. Many cities will double or quadruple in size in a matter of a few years， so will need complex urban systems and infrastructure to function， but we know that major infrastructure projects regularly take over 10 years to scope， design and deliver. Providing sufficient social， transport， water， sanitation and energy infrastructure quickly will be challenging. Housing， particularly affordable housing， will be critical as it is predicted that by 2030 two billion people will be living in slums. Water supply will be difficult in many areas， particularly where water is being extracted faster than it is being replenished， such as the Ogallala reservoir in the USA， which is being drained 100 times faster than it is being replenished. Sharing watercourses can lead to potential tensions; there are over 250 international watercourses that are shared between more than 2 nations. Supplying sufficient and reliable energy will be a key problem， compounded by the need to move away from fossil fuels. Transport is essential for a city to function， but there will have to be a shift from cars to public transport systems， but they typically take years to develop. Food provision will have to change， as the devastating impact of intensive farming on both green house gas emissions and the physical environment is better understood. We currently produce mountains of waste， so we to reduce the amount produced and recycle and reuse materials.
All of these challenges will demand innovation and new ways of doing things， if we are to preserve the planet and create liveable cities that are in tune with the Earth’s bio-systems. We need to understand our ecological footprint and the implications of our actions. We will have to develop renewable energy sources， infrastructure based on low carbon energy sources and we will need to waste less and learn to recognise and value the embodied water and carbon in the products that sustain us. Food production will have to move away from intensive agriculture to smaller organic farms， much of which can actually be provided within our cities. Public transport will have to be the primary form of movement within the city， with a high proportion of journeys by walking and cycling， so our cities will need to be designed to encourage this. Cities will need to have sufficient affordable housing; probably 50% of all housing should be affordable， which will require new mechanisms for funding and delivering this.
There are numerous examples worldwide of innovation and sustainable practice， such as decentralised energy systems， using waste heat from industrial processes， growing organic food on waste land， bringing rivers out of sewer pipes， restoring natural habitats， new ways of delivering social housing and creating buildings that are carbon neutral. Alternative practices need to be encouraged and innovation should be supported. The many thousands of small projects that are already being developed will need to be scaled up from the local to the city scale and need to be supported by governments and delivery agents. The starting point must be a strong vision that is underpinned by strategic and integrated forward planning. The overarching emphasis should be on liveability and sustainable communities. Change comes at a cost and will require some modest behaviour change， but this change can be relatively painless if governance structures support a migration to sustainable practice and we all embrace new ways of doing things. I believe future cities can be wonderful liveable cities that are clean， beautiful， diverse and exciting places to live. The key is to look to the innovators and advocates for sustainable practice for the answers to the problems， rather than always falling back on the expedient solutions in our rush to stay abreast of growth.
An outline of Future Cities by Camilla Ween， published by Hodder & Stoughton / McGraw Hill， available on Amazon and other booksellers.
Review：
Alan Altshuler， Professor Emeritus：
Harvard Kennedy School and Graduate School of Design.
“Wise， comprehensive in its statement of the issues， and peppered with valuable examples from across the globe， Future Cities provides a superb introduction to the challenges of sustainable urbanization. I hope it will be widely read， and influential.”
The predicted population of 10 billion by 2100 （some even predict 11 billion） and the rapid growth of megacities will throw up many challenges. These growing cities will need major infrastructure to cope and it is easy to wonder whether future cities will be places of chaos and inequality， with shortages of essential services， energy and food.
The challenges are great. Tackling CO2 emissions is probably the most urgent and difficult challenge in the Anthopocean era， as we are currently producing more CO2 than the Earth’s ability to absorb it. As almost all city activity is responsible for greenhouse gas emissions （the UN estimates cities to be responsible for 70% of global CO2 emissions） society will have to find new low carbon solutions. There are many fanciful ideas about engineering our 7way out of the climate change predicament， such as fertilising the oceans to encourage phytoplankton to absorb CO2 or peppering the stratosphere with trillions of reflective discs to deflect the sun’s rays， but the more reasonable approach will be to find carbon neutral solutions for our cities and to modify our behaviour somewhat.
The rate of growth of cites is staggering; we currently have 10 megacities （over 10 million population）， but in the coming decade this will rise to 37， two of which will have over 40 million inhabitants. There will be rapid migration from dispersed rural settlements to cities; the current 50-50 split between urban and rural populations will rise to 60% living in cities by 2030 and 70% by 2050. Many cities will double or quadruple in size in a matter of a few years， so will need complex urban systems and infrastructure to function， but we know that major infrastructure projects regularly take over 10 years to scope， design and deliver. Providing sufficient social， transport， water， sanitation and energy infrastructure quickly will be challenging. Housing， particularly affordable housing， will be critical as it is predicted that by 2030 two billion people will be living in slums. Water supply will be difficult in many areas， particularly where water is being extracted faster than it is being replenished， such as the Ogallala reservoir in the USA， which is being drained 100 times faster than it is being replenished. Sharing watercourses can lead to potential tensions; there are over 250 international watercourses that are shared between more than 2 nations. Supplying sufficient and reliable energy will be a key problem， compounded by the need to move away from fossil fuels. Transport is essential for a city to function， but there will have to be a shift from cars to public transport systems， but they typically take years to develop. Food provision will have to change， as the devastating impact of intensive farming on both green house gas emissions and the physical environment is better understood. We currently produce mountains of waste， so we to reduce the amount produced and recycle and reuse materials.
All of these challenges will demand innovation and new ways of doing things， if we are to preserve the planet and create liveable cities that are in tune with the Earth’s bio-systems. We need to understand our ecological footprint and the implications of our actions. We will have to develop renewable energy sources， infrastructure based on low carbon energy sources and we will need to waste less and learn to recognise and value the embodied water and carbon in the products that sustain us. Food production will have to move away from intensive agriculture to smaller organic farms， much of which can actually be provided within our cities. Public transport will have to be the primary form of movement within the city， with a high proportion of journeys by walking and cycling， so our cities will need to be designed to encourage this. Cities will need to have sufficient affordable housing; probably 50% of all housing should be affordable， which will require new mechanisms for funding and delivering this.
There are numerous examples worldwide of innovation and sustainable practice， such as decentralised energy systems， using waste heat from industrial processes， growing organic food on waste land， bringing rivers out of sewer pipes， restoring natural habitats， new ways of delivering social housing and creating buildings that are carbon neutral. Alternative practices need to be encouraged and innovation should be supported. The many thousands of small projects that are already being developed will need to be scaled up from the local to the city scale and need to be supported by governments and delivery agents. The starting point must be a strong vision that is underpinned by strategic and integrated forward planning. The overarching emphasis should be on liveability and sustainable communities. Change comes at a cost and will require some modest behaviour change， but this change can be relatively painless if governance structures support a migration to sustainable practice and we all embrace new ways of doing things. I believe future cities can be wonderful liveable cities that are clean， beautiful， diverse and exciting places to live. The key is to look to the innovators and advocates for sustainable practice for the answers to the problems， rather than always falling back on the expedient solutions in our rush to stay abreast of growth.
An outline of Future Cities by Camilla Ween， published by Hodder & Stoughton / McGraw Hill， available on Amazon and other booksellers.
Review：
Alan Altshuler， Professor Emeritus：
Harvard Kennedy School and Graduate School of Design.
“Wise， comprehensive in its statement of the issues， and peppered with valuable examples from across the globe， Future Cities provides a superb introduction to the challenges of sustainable urbanization. I hope it will be widely read， and influential.”