The writer is executive director of the UN Environment Programme
Cities provide something for everybody: opportunities for employment and entertainment; diversity and density, social benefits as well as social tensions. Yet the world’s greatest metropolises — from Bangkok to Barcelona, Bogotá to Cairo, Damascus to Delhi, Karachi to Kolkata and New York to Nairobi — also hold environmental dangers for their residents.
While many of these — notably waste, biodiversity loss and warming — are already well-documented, there is another often ignored environmental threat having an increasingly significant impact on city dwellers: noise.
Much like air pollution, noise pollution is far from being a mere nuisance. In fact it is increasingly understood to have long-term effects on human health. Defined as unwanted, prolonged and high-level sounds, it can seriously impair our physical wellbeing. This includes chronic annoyance and sleep disturbance, resulting in severe heart disease and metabolic disorders such as diabetes, as well as hearing impairment and poorer mental health.
As cities become more crowded, their soundscapes become a global public health menace. Acceptable noise levels, as defined by the World Health Organization, are now surpassed in cities across the world. An estimated 90 per cent of New York City mass transit users are exposed to levels exceeding the recommended decibel limit. In Ho Chi Minh City, cyclists are exposed to noise levels above 78dB, which can cause irreversible hearing loss. In the EU, noise pollution affects one in five citizens and leads to 12,000 premature deaths every year.
In her book, The Death and Life of Great American Cities, Jane Jacobs wrote that cities can provide something for everybody only because, and only when, they are created by everybody. That egalitarian ideal is rarely realised today. Cities, especially in low-income countries, are marked by social inequality and geographical segregation.
Noise pollution particularly affects the very young and the elderly among marginalised communities that tend to live in proximity to high traffic roads and industrial areas rather than close to green spaces.
As most of the world urbanises, cities are becoming an increasingly important ecosystem, not just for humans, but for biodiversity as a whole. Noise pollution is also a threat to animals, altering communications and the behaviour of various species, including birds, insects, and frogs.
However, research makes clear that natural sounds, emanating from green urban spaces, can offer various health benefits. In some cases, vegetation in urban environments can absorb acoustic energy and diffuse noise. Tree belts, shrubs, green walls and green roofs not only help amplify natural sounds by attracting wildlife, but improve the visual streetscape as well. While the ultimate solution to noise pollution is its reduction, rows of trees planted behind highways have been reported to reduce noise levels by up to 12dB in certain locations.
City planners should take both the health and environmental risks of noise pollution into account. Good measures have been applied already in urban areas across the world: from London’s Ultra-Low Emission Zone, “noise radar” in Paris and Berlin’s new cycle lanes on wide roads to Egypt’s national plan to combat noise and Pakistan’s 10bn trees “tsunami”.
Yet much more is needed to tackle the din in much of the world’s cities. Noise pollution is not a mere inconvenience, but a serious health and environmental issue. Nor is it an unavoidable part of urban life. In recent years, there has been a great mobilisation of resources to combat air pollution, which is responsible for the premature death of more than 7mn people a year. Cities need a similar campaign waged against the cacophony that is harming people and planet.