The Green Soul of the Concrete Jungle
On an increasingly urban planet, human society could face escalating mental health issues unless steps are taken to ensure greater access to nature and green spaces in our cities. The 21st century could be called the urban century, with 2.4 billion more people forecast to live in cities by 2050. In a recent essay in Sustainable Earth, my coauthors and I reviewed three different academic disciplines—urban economics, environmental health, and ecology—to quantify what role nature might play in this urban century. Trends in these three disciplines suggest that the urban century needs nature to succeed.
The first discipline we reviewed was urban economics, which has focused on the positive benefits to individuals, firms, and societies of life in urban settlements. One economist, Edward Glaeser, even referred to cities as mankind’s greatest invention. The major theme is that proximity—the increased potential for interaction that comes from living at higher population density—has its benefits, such as increased economic productivity, patent generation, and innovation. Aristotle famously referred to human as a social animal, by which he meant that our unique skill and love for interacting with one another is part of our species’ essence. In cities, we are creating the perfect space for social interaction. Cities could therefore be seen as quintessentially human, an expression of our deep need for social interaction.
The second discipline comes from environmental health studies of the urban health penalty. There is a clear trend toward an increased prevalence of some mental health disorders in cities. One study in Sweden of more than 4 million adults found a significant increase in the incidence of psychosis and depression among populations living at higher densities in cities than those living in more rural areas. There are multiple possible pathways by which the urban environment and its increased pace and interaction can increase stress and the prevalence of some mental disorders. Cities create a local environment with far different environmental conditions than the ones we evolved as a species to handle. Thus, in this sense, the urban environment can be shockingly inhumane, by not being in accord with our organism’s design and capacities.
The third discipline we reviewed is one that is that of urban ecologists. The central idea of this literature, coming out from the ecology and health fields, is that interacting with nature has health benefits. This occurs through multiple pathways. For example, parks and open space can help encourage recreation, which can help reduce obesity. Trees can help clean and cool the air, while natural habitats can reduce the risk of flooding. There are a growing number of studies that show a psychological benefit of interaction with nature. For instance, Cox and colleagues studied individuals in southern England, and found that neighborhoods with more than 20% forest cover had a 50% lower incidence of depression and 43% less stress.
Knowledge of the dose-response curve of nature’s effect on mental health is still imperfect. Still, given that humanity is in the midst of the fastest period of urban growth in our species history, it seems worthwhile to ask: what fraction of the world’s urbanites get enough nature now? To address this question, we examined forest cover data for 245 cities globally.
Currently, only 13% of urban dwellers live in neighborhoods with more than 20% forest cover, the amount found by Cox and colleagues that provides a protective affect against depression and stress. Despite our growing scientific knowledge of the value of nature for mental health, our urban world
So, what can be done to change this picture, to make the urban century greener? The most important step is perhaps to recognize that nature in cities is not a mere amenity, a “nice to have” thing on par with other urban amenities. Rather, nature in cities is a way to counteract the inevitable psychological downside of increased interaction in cities. Nature in cities is a way to have our cake and eat it too, to have the benefits of an urban world while still having a more humane, more natural life. Nature for urban dwellers then seems more like an essential feature of successful urban century.
We explore in our Sustainable Earth essay particular policies or programs that might help with this change in mindset, such as:
Green Prescription Programs
Doctors in New Zealand can write prescriptions for patients, requiring a certain period of time outdoors in a park or natural area. For every ten green prescriptions written, participants achieved 150 minutes of exercise, which was associated with a 20-30% reduction in all-cause mortality.
Biophilic Urban Design
A new way of designing buildings and neighborhoods tries to integrate natural elements into our cities. One commonly cited example of such a strategy is Singapore, which requires new building to replace all or more, of the nature lost at ground level by designing in space for nature on roofs or walls.
We believe the scientific evidence suggests that interaction with nature is essential to achieving UN-Habitat and its New Urban Agenda, and policymakers should explicitly say as much. If we do not build some nature into our cities, we risk creating an inhumane, grey world for ourselves. Without nature, the urban century will fail.
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