With two-thirds of people expected to live in cities by 2050 and with urban areas accounting for 70 per cent of the emissions that are propelling the planet into a climate unknown, the challenge is both clear and urgent: cities must be reimagined.
"We are at a tipping point," says Martina Otto, head of the Cities Unit at UN Environment. "We have seen sub-national and local governments stepping up and taking forceful commitments, for example, at the recent Global Climate Action Summit in San Francisco. While it is increasingly recognized that urban planning is critical, in many places planning capacity is lacking."
For Otto, what is needed is a "planning revolution" that yields strategically structured, compact cities with mixed-use neighbourhoods and buildings, and with an emphasis on integrated urban systems. She would also like to see green roofs and walls and biodiversity corridors; decentralized energy systems, complementing grids and powered by renewables; and a better use of spare capacity through a sharing economy.
In a report this year, the International Resource Panel said cities must be low-carbon, resource-efficient and socially just. The expert group, which was set up by UN Environment, said urban demand for resources could rise by 125 per cent by 2050 with at least 200 new cities expected to be built in Asia over the next 30 years.
"We have a once-in-a-lifetime opportunity to shift the expected urbanization onto a more environmentally sustainable and socially just path," the report said. "Decisions made today on urbanization and land-use models, as well as on critical infrastructure, will determine whether our investments are future-proof or whether they in fact lock us into an unsustainable path."
In 2015, UN member states signed up to the Sustainable Development Goals, which include specific targets (SDG 11) to make cities and settlements "inclusive, safe, resilient and sustainable". Otto says much work remains to be done as we are "still far from the level of implementation that we need to see".
Steps are being taken. In August, 19 cities committed to significantly cut greenhouse gases by ensuring that new buildings are net zero carbon by 2030, with all buildings meeting this standard by 2050. Net zero carbon means that the total amount of energy used each year equates to the amount of renewable energy created on the site and requires reduction of energy intensity of buildings as a precondition.
Launched by the World Green Building Council, the pledge was backed by C40 Cities, a network of the world's megacities committed to addressing climate change by sharing knowledge and implementing meaningful action. It is also in line with the objective of the UN Environment-hosted Global Alliance for Buildings and Construction to move "towards a low-emission, efficient and resilient building and construction sector".
Thirty-six cities have joined UN Environment's District Energy in Cities Initiative, which supports local and national governments to accelerate investment in modern, district energy systems using underground insulated pipes to pump hot or cold water to multiple buildings to create synergies between the production and supply of heating, cooling, domestic hot water and electricity, and make use of surplus heat and cold, and local renewable sources.
These kinds of pioneering solutions to address environmental challenges will be at the heart of the fourth UN Environment Assembly next March. The meeting's motto is to think beyond prevailing patterns and live within sustainable limits.
This is particularly true in relation to urban transport. Some countries, such as Britain, Denmark, France, Germany, and Norway, are planning to ban the sale of new diesel and petrol cars in the next few decades. In Madrid, 24 streets are being redesigned for walking and by 2020, cars will not be able to drive in 500 acres of the centre. In Italy, all fossil fuel vehicles will be banned from Milan's historical centre by 2029.
Reducing emissions from cars is clearly key but improving public transport networks is also critical. A report by C40 Cities, the Global Covenant of Mayors for Climate and Energy and the New Climate Institute showed that climate action, such as doubling bus network coverage and frequency in cities, could prevent the premature deaths of over one million people per year from air pollution and traffic accidents.
In 2013, the Australian city of Adelaide introduced the world's first electric, solar-powered bus, and there are other examples in Britain and the United States.
The Chinese city of Shenzhen has become the first city to make all its public buses--more than 16,000 vehicles--electric. In Zhuzhou, authorities are operating an electric "trackless train" that uses sophisticated sensors to follow pre-planned routes. However, there is still an environmental price to be paid if the electricity powering the buses is mainly generated from coal.
In Tallinn, Estonia, authorities have introduced Europe's largest free public transport system with residents and students able to travel free on trams and buses. Launched in 2013, the scheme has already led to a 7.5 per cent annual decrease in congestion in the city centre.
In Vietnam, authorities in Ho Chi Minh City launched the Green Transport Development Project, with the World Bank, to cut congestion and reduce road deaths. The key element is a 23-km bus rapid transit system that will be able to carry around 28,300 passengers every day.
Buildings will also have to be transformed. Many cities are working to integrate sustainability into building codes and regulations, sometimes with support from the Building Efficiency Accelerator, a public-private network linked to the United Nations Sustainable Energy for All initiative.
Mexico City has drafted new regulations, including energy efficiency measures for new and retrofitted buildings. In the Brazilian city of Salvador, builders are offered a discount on property taxes if they use sustainable technologies and reduce emissions. Chile's capital Santiago is investing in energy efficiency upgrades and renewable energy projects, including rooftop solar projects.
Waste management also poses a major challenge, but innovation is happening here too. In China, Ningbo has received World Bank backing for an advanced waste separation, collection and treatment strategy that is meant to encourage recycling. In Delhi in India, where over 9,000 tonnes of waste are generated every day, a composting plant was reopened to produce compost and resource-derived fuel from municipal waste. The plant handles 200 tonnes of waste per day, but that capacity is due to be expanded.
Otto notes that developing countries are often not equipped to keep pace with the speed of urbanization. A major problem is the lack of data and the capacity to analyze it. Authorities also need support in devising and enforcing sustainable planning and cross-sectoral policies.
"We cannot afford to get the infrastructure investments, which will be made over the next 15 years, wrong," Otto says. "Areas key for addressing climate and air quality, as well as citizens' well-being, are energy systems, mobility and buildings, all requiring long-term investments that lock us in for decades to come-- we need to make sure that they lock us in on a sustainable urban development path."
Ahead of the United Nations Environment Assembly next March, UN Environment is urging people to Think Beyond and Live Within. Join the debate on social media using #SolveDifferent to share your stories and see what others are doing to ensure a sustainable future for our planet.