On World Environment Day, conversations about sustainability often focus on reducing pollution or protecting biodiversity, which are indeed very relevant topics for ensuring that humanity remains within the planetary boundaries. Additionally, an increasing body of scientific evidence highlights another important reason to create greener cities: our mental health depends on it.
Recent research published in Nature Cities (2025), based on a systematic review of the scientific literature, shows that contact with urban nature provides substantial benefits for a broad range of mental health outcomes. Spending time in parks, tree-lined streets, or other green spaces has been associated with lower stress levels, improved mood, reduced anxiety, and better cognitive functioning. Importantly, these benefits do not require access to large natural areas. Small green spaces integrated into daily urban life can make a meaningful difference.
These findings reinforce a growing consensus among researchers: green spaces should not be viewed only as aesthetic additions to cities, but as essential infrastructure for public health. As urban populations continue to grow, ensuring access to nature becomes increasingly important for promoting healthier and more resilient communities.
However, scientific evidence raises an important question: if greener cities improve well-being, how can such transformations be achieved?
A recent study published in Urban Science explores the role that a working-class neighborhood played in redefining its environment and shaping a more inclusive and sustainable urban future through collective agency. Specifically, this study shows how La Verneda-Sant Martí Adult School, as a grassroots actor, has contributed to urban regeneration by linking environmental demands with broader struggles for social dignity, health, and community cohesion. This insight is particularly relevant today, as citizens who organise actions around environmental and social goals can help bring scientific knowledge into public debate and support changes that improve the quality of life for entire communities.
The connection between these two studies offers a powerful message for World Environment Day. Science tells us that greener cities contribute to healthier minds. At the same time, research on grassroots movements reminds us that urban transformation is not something that happens only from the top down. It can also emerge from the collective action of citizens committed to improving their communities.
Building greener cities is therefore not only an environmental challenge. It is also a public health opportunity and a collective responsibility. The scientific evidence is clear: greener cities support healthier and more resilient communities.
Associate Professor in the Department of Sociology at the University of Barcelona