The future of cities is often mentioned, at least in developed countries, through the futuristic vision of « smart cities », sober in energy, but the reflections on the energy transition rarely take into account the complexity of urban issues. We must begin with a simple observation: while the share of the urbanized world population has surpassed the 50% threshold in 2008, we will have 60% of urban people in 2030 and two at least two thirds of the 10 billion of the planet inhabitants will be urbanized by 2050 (see Sueur, JP., Report on the cities of the future, Senate Delegation to the prospective, Senate 2011 www.senat.fr ). Megacities like London, New York, Paris, Beijing and Tokyo are heavy energy consumers within congested transportations, buildings, residences and offices; the 600 largest world cities account for only a quarter of the world population but contribute 60% of its GDP. We are witnessing around the world the development of « suburban » territories, an extension of the inner suburbs where roads are built in the vicinity of residential areas with large shopping complexes and an anarchic urbanism. The inhabitants of the suburbs, in Europe and North America, are compelled to use a car to go to work or to shop in commercial areas outside the cities, which is a supplementary source of energy consumption. It is thus found that in most developed countries, 65% of kilometers traveled by cars and 70% of fuel consumption are for local travel. What would be the relationship between the city of the future and energy? Most of developed countries in Europe, North America and Japan, will probably envisage “post-carbon” cities or still better  » sober cities «  whose energy consumption would be under control in transport and buildings (cf. Haëntjens, J. frugal city, Limoges, FYP Editions, 2011. “The post-carbon society”, Futuribles special issue, No. 392, January-February 2013, www.futuribles.com ).  In France, in 2014, energy demand for transport accounted for 32% of its final energy consumption, and buildings for 42%. A recent report by the French General Commission for Sustainable Development (“Rethinking cities in the post-carbon society” www.developpement-durable.gouv.fr/IMG/pdf/ED119 ) points out that tomorrow’s cities in France and Europe, will have to divide by three or four their greenhouse gas emissions and be oil independent and eventually adapt to a 2 to 4 ° C global warming by the end of the century. Cities in industrialized countries account for two-thirds of energy consumption and greenhouse gas emissions in those countries. This report proposes six scenarios for future cities ranging from « intelligent wait and see » (which is not viable) to a « sober urbanity » which implies a values reversal involving with a reclaiming of public grounds with high quality public services. This requires action within space and time. A proactive public transport policy and city planning should certainly help achieving  by 2050-2060 the objective of reducing energy consumption in cities by 2050-2060, but it is a huge challenge as most of the housing and office portfolio of European Cities of 2050 is already built (in Europe, the park built each year represents on average 1% of the existing real estate stock). Futuring a post-carbon city assumes a continuous and sharp decrease in the consumption of fossil fuels, but the major European cities have few ground left to build housing that would be energy self-sufficient. Much more, the financial cost of a thermal renovation of buildings policy as it is planned in the energy transition Law which is being discussed in France (500,000 buildings renovated per year) will be high (10 to € 15 billion by year cf. IDDRI SciencesPo, A. Rüdinger, How to finance the energy transition? www.iddri.org ). A « smart » urbanism might envisage building small boroughs or “villages” within large cities requiring a public transport policy and a large-scale vehicle electrification but it would imply significant investment. In fact, the real debate on the possibility of designing and implementing « sober energy cities” consistent with the energy transition, will concern in priority Africa and Asia where large urban concentrations are being multiplied as Lagos in Nigeria and in many Chinese cities. A recent study by the World Bank on urban growth in East Asia (analyzed by Yann Futuribles Vigie in March 2015, www.futuribles.com ) indicates that urban area increased in this region from 106,000 km² to 135 000 km² between 2000 and 2010, China’s urban population increased from 346 million to 477 million over the same period. This report identifies 869 urban areas with more than 100 000 inhabitants in East Asia, with eight megacities of more than ten million inhabitants and their number will keep growing. Urban areas are those where per capita income is higher and, presumably, the energy consumption as well. Administrative fragmentation (seven prefectures for Greater Tokyo and eight departments for the Grand Paris!) does not facilitate urban planning in relation to an energy saving policy. Rapid urbanization in Africa also poses a serious problem: 45% of Africa population is urbanized today, while it will have at least 2 billion people in 2050 with a urban population having doubled, India will probably face the same situation. How will we master the energy consumption of a city like Lagos, which could reach 40 million by 2050? (Photo : C. Lüthi , ETH Zürich, suburbs in Nairobi) We can assert that energy consumption management in Asian cities and Africa, and probably in Latin America, is a real challenge for the energy transition. Indeed, the attractiveness of cities on rural populations will inevitably cause an increase in energy demand per capita. The modern city tends to increase electricity and transport fuel demand, as energy, it is true, is improving life conditions. The global car fleet, mainly used for urban and peri-urban travel, exceeded one billion units in 2010, it has nearly reached 1.5 billion vehicles and might reach three billions by 2050 (beyond a certain limit, increasing the number of vehicles would lead to the total traffic congestion and regulatory measures ….). Assuming that each new city dweller in the world would consume 2 toe per year on average in 2050 (the figure of 2 toe being the primary energy consumption per capita in China in 2011, a still very rural country) it is estimated that a rise in global urban population of 2.5 billion, likely by 2050 migration or natural increase, would mechanically result in an increase in energy consumption by 5 Gtoe which is far from negligible. Energy consumption in rural areas in Africa and Asia is still low, people often do not have direct electricity access.

Urbanization with Chinese energy consumption standard of the 2010s would represent a considerable improvement in living standards but would weigh on the global energy consumption. This figure shows the magnitude of the challenge represented by the energy transition for cities. Several European cities (Freiburg, Germany, Stockholm, Bristol and Grenoble, for example) have pioneered urban planning with « low carbon » energy. This implies for the future a territorial policy to find a good balance between large and medium size cities – excessive concentration of population in megacities inevitably leading to wasting energy – with a minimum of planning, particularly in Africa and Asia. The role of the city will not change, it will remain a motor of history, but it will be imperative to develop or build it in order that it would preserve the planet’s resources, especially energy.