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Dreaming cities

Cities and the low-carbon challenge

Moving towards the decarbonised city means rethinking our ways of living, consuming and getting around. What are the keys to change? Innovation of course, though on condition that it is supported by the commitment of decision-makers and the awareness of citizens. More and more densely populated, increasingly polluted and congested, cities produce three-quarters of greenhouse gas emissions and consume two-thirds of the world’s energy. The main offenders in terms of global warming, they are also its main victims: around 70% of them are already suffering its effects, and almost all are under threat.

A question of balance

With the commitment in 2015 by all countries of the world to reduce their emissions and keep warming below 2°C by 2100, the Paris Agreement, signed at COP21, marked a turning point. Today, given the urgency, the movement is accelerating and cities are at the forefront. Everywhere in the world, they are rallying together, putting climate action at the top of the agenda. They are no longer aiming simply to reduce their greenhouse gas emissions but to achieve carbon neutrality. What is the goal? To reach a balance between CO2 emissions and their absorption by natural reservoirs, such as oceans, soils and forests.

At the end of 2020, around a hundred local authorities in France and abroad, including Los Angeles, Kinshasa, London, Lyon, Marseille and Paris, signed the Paris Declaration, committing to act more quickly to achieve carbon neutrality. As for the EU, it wants to see 100 European cities reach this goal by 2030 and is supporting this effort with the “Climate Neutral and SmartCities” mission within its Horizon Europe programme.

Riyadh, city to live

In a rapidly urbanising Saudi Arabia, the authorities want to make Riyadh a smart and sustainable showcase, and one of the world’s most agreeable cities to live in. Four major environmental, sporting and artistic projects, in line with the United Nations Sustainable Development Goals, support this ambition, which also involves drastically reducing traffic congestion by creating the city’s very first public transport system (automated metro and bus). Implementing this change has been entrusted to RATP Dev, in partnership with Saudi operator SAPTCO.



8 million

inhabitants in 2030 compared with 5.2 million in 2010: this is the population growth expected for Riyadh.

Political impetus

The good intentions are there, but how does one move from goals to concrete results? To succeed, cities, prime examples of complex organisations, must simultaneously activate a large number of levers: converting their transport systems to use clean energies, but also improving the energy efficiency of buildings and infrastructures, better managing waste and promoting recycling while renovating urban infrastructure in a sustainable approach. To meet these challenges, innovation can play a key role, provided that the political will and regulatory framework are in place. In the building sector, responsible for 39% of greenhouse gas emissions worldwide, the technical solutions have been around for a long time.

In Canada, Taiwan and Singapore, high-efficiency buildings put up in the 1970s are still performing well today. So why aren’t there more of them? Because a strong impetus is needed for these good practices to become widespread. This is what has happened in Brussels, New York and Vancouver. In the 2000s, buildings in Brussels were among the least efficient in Europe. By incorporating passive construction principles into its regulations, the city has reversed the trend in less than ten years. In Vancouver, a city engaged in a similar process, the low-carbon economy market is now estimated at $3.3 billion for the period 2019-2032.

London, green city

As the first capital in the world to be designated a “national park”, London deserves this distinction: public green spaces cover more than 16% of Greater London, compared with 8.8% for Paris. But being green isn’t enough. The city road map aims for a zero-emission transport system by 2050. To get there, the city introduced very low emission zones in 2017, which will become zero emission zones starting 2025. And it has invested to convert its bus fleets to run on electricity or hydrogen.




buses in London will be zero carbone emission by 2037

Strategies to combat global warming

The path to carbon neutrality also involves adapting urban space and buildings to the climate, which is necessary to limit the phenomenon of heat islands and avoid wide spread use of air conditioning. Here again, innovation is central to organising the response. Using satellite images or climate simulation tools, cities are starting to organise their urban fabric by designing buildings in a way that encourages air circulation. By forbidding construction in strategic locations, Stuttgart has created air corridors that prevent hot air from stagnating in order to naturally cool its streets.

More and more local authorities are setting permeable ground targets, to allow water evaporation. They encourage installation of pavements that do not store heat, such as grass pavers, and are testing colours that do not absorb heat. In 2017, Los Angeles lowered the temperature in some districts by 10°C by painting the roads white. In Qatar, the city of Doha opted for blue on a test section, to reduce the temperature of the asphalt from 20°C to 15°C.

Sydney, a sustainable city

Sydney is aiming for carbon neutrality by 2050 and is using various levers to achieve it: planting 800 trees a year to double forest cover and refresh the city, choosing LEDs for urban lighting, and moving to renewable energies. Since July 2020, all public infrastructure (traffic lights, municipal swimming pools, city hall, etc.) in the central City of Sydney district have been supplied by solar or wind power.




of forest cover in 2050, compared with 15.5% in 2013: that is the goal of the city of Sydney.

Urban clealiness and fluidity

Refreshing and greening the city is essential, but there is also a need to tackle urban congestion by breaking out of the all-car model. The 35 member cities of the C40 Cities network, signatories of the “declaration for greener and healthier streets”, have pledged to buy only zero-emission buses as from 2025 and to ensure zero emissions by a significant part of their public transport networks by 2030. At the same time, many cities are striving to break out of the all-car model by encouraging a move from single-driver vehicles to active or shared modes, powered by clean energies, such as bicycles, scooters or electric minicabs. And they are taking a fresh look at mobility issues, drawing inspiration from the 15-minute city for example, a planning model based on being able to shop, work, have fun and play sport within a radius of around 1 kilometre from home.

By making this transition to carbon neutrality, cities also strengthen their ability to be resilient. The emergence of cities that are more self-sufficient in energy, better prepared to anticipate and manage risks, is very good news for their residents. A major part of the solution is in their hands. Their awareness of these subjects and the education of the youngest remain essential levers in rising to the challenge of changing model. “Communities are innovative, resilient and proactive. They play a vital role in building economically, socially and environmentally sustainable cities. Let us maintain this recognition of their value,” said António Guterres, Secretary-General of the United Nations, during World Cities Day in October 2020.

Medellín, a committed city

Since the 2000s and despite the difficult circumstances which Colombia currently faces, the country’s second city has been pursuing a policy of reclaiming its urban area and combating poverty, through urban planning and public transport in particular. In this city surrounded by mountains, the metro connects with both an urban cable car, which makes some of the poorer districts accessible, and exterior escalators that facilitate traffic flows. The next goal is to become the Latin American capital in electric mobility, through the energy conversion of its public transport and taxis.



Nearly 400 m:

the length of the giant escalator that serves Comuna 13, one of the highest districts in Medellín.

From Paris to London, the same ambition

On both sides of the English Channel, RATP Group is putting innovation at the service of sustainable urban transformation. Following the decision by Île-de-France Mobilités to withdraw diesel buses from the Paris-region network, RATP has been engaged since 2014 in a major technological change, the conversion of all its bus depots to electricity or biomethane by 2025*. Unique in Europeon this scale, the process began with a vast programme of electric bus experiments in real operating conditions, to trial the different available technologies, the charging systems and the maintainability of the equipment. It continues today with the conversion of the bus depots to biogas or electricity. At the end of 2020, four bus depots had been converted. Works on another eight is in progress. For all the other depots, the transformation is under way. In London, with a similar industrial transformation effort to support the city’s carbon neutrality commitments, RATP Dev has become the leading electric fleet operator in the British capital. At the start of 2020, after routes C1 and 70, RATP Dev London fully converted to electricity a third bus route (94). This is the first bus route using London double-deckers to go electric. By 2022, electricity will have a 24% share in the network operated by RATP Dev London, with 15 routes operated and 5 depots converted. The subsidiary will be operating a total of 260 electric buses.


*In 2020, the European Commission granted a first €23 million subvention for the purchase of electric buses and the conversion of bus depots to electric (for the Lagny, Corentin, Pleyel, Lilas and Lebrun bus depots) and biogas power (for the Massy, Bussy, Thiais and Nanterre bus depots). In 2021, a second €27.7 million subvention was granted for the further conversion of bus depots to electric (for the Point du Jour, Croix Nivert, Neuilly, Vitry, Belliard bus depots) and biogas power (for the Aubervilliers bus depot). With the funding, the Commission supports Île-de-France Mobilités’ and RATP’s commitment to their energy transition set out in the Bus2025 programme.


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