Over half the world’s population currently reside in cities, a figure projected to grow to nearly 70% by 2050. Despite occupying only 3% of the planet’s land, cities account for over 70% of carbon emissions and resource consumption, putting them at the forefront of climate mitigation and sustainability needs. This concentration of people, consumption, and activity magnifies global heating effects, making urban communities warmer than their surrounding landscapes, while increasing congestion in the form of pollution and noise, which can leave residents at risk of health consequences. To transition towards sustainable urban systems and meet global emissions targets, it will require policy frameworks, targeted investments, and collaboration to re-design cities for sustainability which can improve the quality of life for urban populations.
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An Urban Sustainability Crisis
Cities are economic hubs, generating over 80% of global economic activity and providing financial and social opportunities for millions. However, each year, cities consume vast quantities of nonrenewable resources, including energy, water, and raw materials, leading to significant waste generation. The built environment alone is responsible for 40% of global carbon emissions, with construction processes and materials contributing significantly to this footprint, particularly as the world continues to urbanize. The social and environmental repercussions are immense: cities can exacerbate climate change, pollute air and water, and degrade ecosystems. According to estimates by the European Environmental Agency in 2022, 96% of people living in EU cities were exposed to levels of air pollution above the World Health Organization target levels.
Barriers to Urban Sustainability
The main issue is inefficiency. Urban infrastructure is often built for short-term gains rather than long-term sustainability. Poorly designed housing developments, inefficient and environmentally damaging transportation networks, and energy-intensive industries can contribute to a city’s unsustainable footprint. Globally, one-in-four city residents reside in slum housing, which lack water, sanitation, sufficient space, and durable structures. In advanced economies such as the EU, still 75% of building stock in cities is energy inefficient.
Economic barriers also hinder progress. Sustainable solutions such as retrofitting buildings, investing in renewable energy, or creating green spaces often require substantial upfront investments that many cities struggle to afford. Moreover, urban policies frequently fail to incentivize resource-efficient designs or renewable energy integration. The complexity of urban supply chains further complicates matters, as decision-makers lack visibility into material flows and lifecycle impacts that make up the urban footprint.
Regional differences also play a key role. According to the African Centre for Cities, almost all electricity grids in Africa experience frequent outages, and clean and safe electricity is critical to sustainable development in Africa’s rapidly evolving cities. However, prevailing electricity prices across the region are inadequate, expensive, and unreliable, particularly for sub-Saharan Africa. As Elizabeth Mansfeld, a Senior Advisor on Impact and Specialist on Urban Development explained, “one of the fundamental challenges in urban development is energy supply – it affects transport, water supply, food, health, and communication and any business activities. Even in large cities, power grid shortages remain a pressing issue that must be sustainably addressed as productivity will be key to economic growth.”
Another significant hurdle is governance. Urban areas are often governed by overlapping jurisdictions, creating inefficiencies and conflicts in decision-making. As cities expand and sprawl with population increases, there is demand for new infrastructure. Existing infrastructures for waste management, renewable energy, and public transport often struggle to keep up with growing urban populations, and coordinating this amongst levels of government with sustainability as a priority is challenging. Even within a city, governance and collaboration between departments is not always well-coordinated, which can lead some cities to struggle to be attractive places to live, work, or conduct business. As Peter Griffiths of BABLE Smart Cities told us, “cities need talent and investment. The biggest challenge with cities transitioning towards climate focused objectives is that government and relevant stakeholders are often siloed rather than integrated, reducing impact and frustrating innovation. Sustainability creates the opportunity for helping cities have a long-term vision that connects and integrates their capabilities.”
Toward Sustainable Cities
The UN’s Sustainable Development Goal 11 (Sustainable Cities and Communities), the EU’s Urban Agenda, and the Paris Climate Agreement are notable examples of frameworks driving transformative change towards sustainable cities. Policies such as carbon pricing, low-emission zones, zoning laws for mixed-use development, and incentives for green technology adoption set the stage for sustainable urban growth.
A main target for sustainable cities is carbon emissions reductions. While national targets at climate neutrality focus on the year 2050, cities are at the forefront of driving this change in the near term. Through the Horizon Europe programme, the EU’s mission for 100 Climate-Neutral and Smart Cities by 2030 aims to see 100 cities in Europe serve as experimentation and innovation hubs to achieve net-zero and enable future cities to follow. These cities create climate city contracts and work across sectors, including energy, buildings, waste, management and transport alongside local stakeholders. As Gratian Mihailescu, founder of Urbanize Hub and Board Member of the 100 Climate Neutral and Smart Cities Project explained, local and national collaboration drives success for sustainable cities. “If the EU continues to invest directly in cities, then municipalities and cities will write projects to attract the investment. We see a lot of grassroots projects from communities, NGOs, and startups where sustainable solutions come from the local level. It’s important to see both bottom-up and top-down synergy between macro policy and local needs.”
The policies that will make cities more sustainable in terms of carbon mitigation and reducing resource consumption include electrifying transport, increasing renewable energy sources, developing adequate green and cooling spaces, supplying adequate and dense levels of housing, and providing clean water, sanitation, and waste solutions. This approach is cross-sectoral and requires integration with the current urban environment, while also being creative about how space is used.
Systems approaches to sustainability
Yet the benefits from sustainable cities extend much farther than meeting climate mitigation targets. Ed Sudall, a Researcher at the Centre for Environmental Policy at Imperial College, specializes in integrating systems thinking approaches to show how urban spaces can be transformed to serve people’s ends through multi-criteria benefits.
In a systems thinking approach, a policy must be evaluated by considering co-harms competing with co-benefits. As Ed Sudall explains, “we need to consider that co-harms are prevailing right now over the co-benefits. There are benefits to mitigation efforts and green infrastructure that contribute to people’s well-being, which in turn has benefits on their productivity.” In other words, there are economic incentives as well that play out both through employment, but also government expenses. “Sustainability should not just focus on the environment, but also the sustainability of finances, because policies and city design can have material costs to government through health damages.”
Resource Use and Circular Consumption
While climate mitigation can lead to multiple co-benefits, for cities to be more sustainable they also require an imagination about how we consume resources. Resource-efficient cities leverage scale to provide services in an integrated way that minimizes energy and resource use while still enabling human activities. Cities require massive flows, stocks, and sinks, of physical and chemical resources through the goods and services that are imported and exported to provide for the urban population and to facilitate its economic development. Yet by tracking material flows in urban areas, city leaders can identify ways to reduce consumption. For example, the industrial district of Kalundborg in Denmark facilitates exchange of by-products that would otherwise be wasted by facilities, which contributes to raw material and cost savings.
The strategies for cities to achieve this type of urban resource efficiency include environmental management-integrated urban planning, and eco-efficiency engineering, which each track the material flows, stocks, and sources at different levels.
There is also a social dimension. When speaking about sustainability in Africa, Elisabeth Mansfeld told us, “people become highly innovative, build their own solutions, often leapfrogging traditional systems with new approaches due to limited resources. They frequently reuse materials rather than discard them, not just out of necessity but as part of an existing social structure. This mindset presents a valuable opportunity to build more sustainable solutions in waste management, sanitation, water infrastructure, and renewable energy, including solar.”
Can Sustainable Cities Be Regenerative?
Regenerative cities refer to the idea that cities can restore, replenish and have positive impacts on communities and eco-systems such that they do not only reach net zero, but go even further to heal environmental conditions. Some of the main features of regenerative cities are nature-based solutions, biodiversity integration and urban re-wilding. By creating circular resource management while making infrastructure such as buildings ‘energy-positive’, cities can not only be sustainable but create positive environmental spillovers. Examples of regenerative practices include waste to resource policies in Curitiba, Brazil, community urban agriculture in Lund, Sweden, and Tokyo, Japan’s Comoris program which plants small forests on unused urban lots to increase tree cover and soil enrichment. Regenerative projects require understanding the unique characteristics of the local environment, species, and eco-systems to be successful, so not every solution will be able to scale across regions.
The promise of regenerative cities is powerful, as the co-benefits from regenerative activities could be transformative to quality of life, with additional co-benefits that could reduce costs for households and for firms. Yet to build sustainable cities, let alone regenerative cities, it will take additional commitment from policy-makers, communities, and the private sector. It will require innovative financing, included blended finance to fund projects at larger scales that can maximize the potential of sustainable and regenerative practices.
