We have entered the urban century and addressing a broad suite of sustainability challenges in urban areas is increasingly key for our chances to transform the entire planet towards sustainability. For example, cities are responsible for 70% of global greenhouse gas emissions and, at the same time, 90% of urban areas are situated on coastlines, making the majority of the world’s population increasingly vulnerable to climate change. While urbanization accelerates, meeting the challenges will require unprecedented transformative solutions for sustainability with a careful consideration of resilience in their implementation. However, global and local policy processes often use vague or narrow definitions of the concepts of ‘urban sustainability’ and ‘urban resilience’, leading to deep confusion, particularly in instances when the two are used interchangeably. Confusion and vagueness slow down needed transformation processes, since resilience can be undesirable and many sustainability goals contrast, or even challenge efforts to improve resilience. Here, we propose a new framework that resolves current contradictions and tensions; a framework that we believe will significantly help urban policy and implementation processes in addressing new challenges and contributing to global sustainability in the urban century. Urban systems must adapt to climatic and other global change. This Perspective uses urban systems to argue that sustainability and resilience are complementary but not interchangeable and that, in some cases, resilience can even render cities unsustainable.

Sustainability and resilience for transformation in the urban century

Defining and advancing a systems approach for sustainable cities

Understanding the dynamics of urban ecosystem services is a necessary requirement for adequate planning, management, and governance of urban green infrastructure. Through the three-year Urban Biodiversity and Ecosystem Services (URBES) research project, we conducted case study and comparative research on urban biodiversity and ecosystem services across seven cities in Europe and the United States. Reviewing > 50 peer-reviewed publications from the project, we present and discuss seven key insights that reflect cumulative findings from the project as well as the state-of-the-art knowledge in urban ecosystem services research. The insights from our review indicate that cross-sectoral, multiscale, interdisciplinary research is beginning to provide a solid scientific foundation for applying the ecosystem services framework in urban areas and land management. Our review offers a foundation for seeking novel, nature-based solutions to emerging urban challenges such as wicked environmental change issues.

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Key insights for the future of urban ecosystem services research

Urban nature has the potential to improve air and water quality, mitigate flooding, enhance physical and mental health, and promote social and cultural well-being. However, the value of urban ecosystem services remains highly uncertain, especially across the diverse social, ecological and technological contexts represented in cities around the world. We review and synthesize research on the contextual factors that moderate the value and equitable distribution of ten of the most commonly cited urban ecosystem services. Our work helps to identify strategies to more efficiently, effectively and equitably implement nature-based solutions. The value of ecosystem services in cities around the world is highly uncertain. This Review focuses on ten of the most commonly cited urban ecosystem services and presents a synthesis of the scholarship on the factors that moderate the value and equitable distribution of such services.

Social-ecological and technological factors moderate the value of urban nature

Urbanization is a global phenomenon with strong sustainability implications across multiple scales. We argue that much of the associated challenges, and opportunities, are found in the global south. We show that urban issues in the global south are distinctly and statistically different from those in the global north, but our current urban knowledge is predominantly shaped by research on and from the global north. Cities in the global south have strong imperatives, and unique but often overlooked capacity, to innovate and experiment for sustainability. We call for a renewed research focus on urbanization in the south, and suggest targeted efforts to correct structural biases in the knowledge production system. Most of the sustainability challenges and opportunities associated with urbanization are found in the global south. This Perspective shows the extent to which urban issues differ between the developed and developing worlds and identifies steps to re-focus the urban research system globally in view of allowing a more prominent role of urban scholarship from the global south.

The urban south and the predicament of global sustainability

Urban ecology is a field encompassing multiple disciplines and practical applications and has grown rapidly. However, the field is heterogeneous as a global inquiry with multiple theoretical and conceptual frameworks, variable research approaches, and a lack of coordination among multiple schools of thought and research foci. Here, we present an international consensus on how urban ecology can advance along multiple research directions. There is potential for the field to mature as a holistic, integrated science of urban systems. Such an integrated science could better inform decisionmakers who need increased understanding of complex relationships among social, ecological, economic, and built infrastructure systems. To advance the field requires conceptual synthesis, knowledge and data sharing, cross-city comparative research, new intellectual networks, and engagement with additional disciplines. We consider challenges and opportunities for understanding dynamics of urban systems. We suggest pathways for advancing urban ecology research to support the goals of improving urban sustainability and resilience, conserving urban biodiversity, and promoting human well-being on an urbanizing planet.

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Christiane Weber

Papers

Advancing Urban Ecology toward a Science of Cities