The biophysical and human worlds are linked in an interwoven planetary system. This blog draws on a recent editorial in UCL Open Environment, which explores how human health depends on finite biophysical processes and the role cities play in delivering solutions to the environmental crises they have helped to create.

Planetary health brings this interdependence into focus. It asks how human health and wellbeing can be sustained without exceeding the planet’s capacity to provide. While these questions operate at a global scale, many of the pressures shaping planetary health and many of the opportunities to address them are concentrated in cities.

Why cities matter

Cities sit at the centre of today’s planetary health crises. Although they occupy a relatively small proportion of the Earth’s surface, cities are now home to more than 55% of the global population and dominate economic activity, energy use and resource consumption.

As a result, cities amplify many of the pressures affecting planetary systems, including greenhouse gas emissions, pollution, water stress and biodiversity loss. At the same time, cities are places where decisions about infrastructure, housing, transport, energy and governance are made every day.

As the editorial argues, cities simultaneously intensify planetary pressures and offer some of the most practical opportunities to address them.

The glass half empty: cities as drivers of harm

Urbanisation has delivered security, opportunity and prosperity for millions of people. But it has also intensified exposure to environmental risks and health harms.

Poor air quality, excess heat, flooding, noise and contamination affect urban populations worldwide, contributing to premature deaths, illness and widening inequalities. Urban development alters land use and disrupts water, carbon, and nutrient cycles, with effects that extend far beyond city boundaries. In many cases, the impacts of these changes are indirect, delayed or geographically distant from the decisions that caused them.

Cities can also shape how people relate to the natural world. There is growing evidence of declining nature connectedness among urban populations, raising concerns about how future decisions will be made in societies increasingly disconnected from the systems that sustain them.

These harms are rarely the result of a single choice or individual. Instead, they emerge from the cumulative impact of many small, often isolated decisions taken by individuals, organisations and governments, none of whom can easily be held responsible for their combined planetary effects.

The glass half full: cities as places of possibility

Despite these challenges, cities also hold significant potential to improve planetary health. Cities are not simply collections of buildings and people; they are complex systems bringing together governance structures, infrastructure, economic activity, cultural life and environmental processes.

This complexity can be a source of solutions as well as problems. Cities concentrate financial resources, expertise, leadership and innovation. In many places, urban authorities are already experimenting with ways to reduce emissions, manage water more sustainably, improve air quality and integrate nature into the built environment.

Examples from cities around the world show that it is possible to reduce environmental risks while delivering wider social and health benefits. These efforts demonstrate that cities can move beyond simply consuming natural capital and begin to regenerate it, particularly when planning and governance are informed by ecological understanding and inclusive decision-making.

The role of research and why openness matters

Research has a central role to play in addressing planetary health, particularly in cities where environmental, social and health systems are closely interwoven. As the editorial makes clear, many of the challenges facing planetary health arise from the cumulative effects of numerous, often disconnected decisions, taken at a distance from the planetary systems they affect.

One consequence of this complexity is the gap between research findings and their practical recognition and use in decision-making. Evidence may exist, but if it is fragmented across disciplines, difficult to access, or slow to circulate, its ability to inform action is limited. Addressing planetary health in cities therefore requires interdisciplinary research that reflects how urban systems function in practice and brings together insights across environment, health, infrastructure and governance.

Access to research is a critical part of this picture. Lowering barriers to publishing and opening access to research findings can help increase the visibility, uptake and impact of evidence. UCL Open Environment contributes to this wider effort by providing an open, equitable space for interdisciplinary research on planetary health and urban systems, supporting the exchange of knowledge needed to better connect research, policy and practice.

Get involved!

Read the full call for papers for this thematic series on Planetary Health, here.

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